StemCell Therapy

Aug 30, 2016

It is important to teach your children about eye health and safety from a young age. This includes awareness about how your overall health habits affect your eyes and vision as well as how to keep your eyes safe from injury and infection. Starting off with good eye habits at...

Aug 19, 2016

Since studies show that learning is 80% visual, children with untreated vision problems can really suffer when it comes to school. Most people think that good vision means 20/20 acuity but in reality, vision is much more complex. Your brain is actually what completes the processing of the visual world...

Jul 30, 2016

We have all seen the futuristic thrillers that use high-tech eye scanning identification systems but nowadays the technology does exist to use them in real life. A greater number of high security establishments have begun to use iris recognition for identification and security systems. How does it work? The...

Jul 22, 2016

There have been a lot of videos going viral lately of color blind people seeing color for the first time using specialized glasses. The emotional reactions of amazement, shock and joy even lead some to break down into tears. The glasses provide these individuals a way to view the world...

Jun 26, 2016

Whether it is the sea, the sand, the sun or the softball field, summer brings people outside and this creates exposure to a multitude of potential dangers to the eyes. One risk that is possibly the least obvious is the swimming pool. Swimming pools are the culprit for multitudes of...

Jun 19, 2016

After the age of 50 most people will eventually be diagnosed with cataracts. Cataracts are when the natural crystalline lens of the eyes become clouded, causing vision impairment that can not be corrected by glasses or contact lenses. While commonly an age-related condition, occasionally there are infants born with a...

May 26, 2016

According to the Vision Councils 2016 UV (Ultraviolet Radiation) Protection report, parents are more likely to wear sunglasses (56%) than their children (only 29%!). Yet children, who spend much more time outside, are typically exposed to three times the amount of sunlight and UV radiation that adults get. This early...

May 18, 2016

UV Awareness Month: This article might scare you, and we hope it does - just enough to motivate you to wear proper eye protection against the sun. Most people are aware of the dangers ultraviolet (UV) light from the sun pose to your skin, while the long-term effects of sun...

Apr 26, 2016

A stye (known by eye doctors as a hordeolum) is an infection of an oil gland which forms a pimple-like bump on the base of the eyelid or within the eyelid itself. Styes can be uncomfortable, causing swelling, pain, redness, discomfort and sometimes excessive tearing or blurred vision if it...

Apr 17, 2016

Along with congestion, runny nose, coughing, sneezing, headaches and difficulty breathing, individuals with allergies often suffer from eye allergies or allergic conjunctivitis resulting in red, watery, itchy and sometimes swollen eyes. Just as irritants cause an allergic response in your nasal and respiratory system, your eyes also react with an...

Mar 30, 2016

If you are over 40 and have difficulty seeing close up, you probably have a common age-relatedcondition called presbyopia which is when the eyes natural lens loses the ability to focus on close objects. Presbyopia is a natural process that occurs as the eye ages and affects the majority of...

Mar 09, 2016

When people think of workplace dangers to the eyes, it is usually machinery, chemicals or construction materials that come to mind. However, a growing danger to the eyes is one that may be less obvious - exposure to blue light from digital devices, television and computer screens and artificial lighting....

Mar 09, 2016

When people think of workplace dangers to the eyes, it is usually machinery, chemicals or construction materials that come to mind. However, a growing danger to the eyes is one that may be less obvious - exposure to blue light from digital devices, television and computer screens and artificial lighting....

Feb 28, 2016

Whether you are looking for regular prescription glasses, sunwear or protective sports eyewear, it can be tough choosing the best eyewear for children and teens. On the one hand, they need to be comfortable and provide the optimal fit for improved vision and protection. At the same time, they also...

Dec 31, 2015

Refractive errors including myopia, hyperopia, astigmatism and presbyopia.

Dec 09, 2015

Tis the season for giving, and parents, grandparents, family and friends need to know how to choose toys and games that protect childrens health and eyesight.

Nov 23, 2015

Have you ever thought about how vision works? It's an incredible system and process!

Nov 02, 2015

Prevention and treatment for eye complications associated with Diabetes

Oct 25, 2015

Beware this Halloween and think before you blink (in decorative contact lenses that is)! Sure, decorative contact lenses can enhance any Halloween costume, but if not taken seriously, they can also cost you your vision. Whether they are sold as cosmetic lenses, colored lenses or fashion lenses, they are anything...

Oct 13, 2015

Home Eye Injury Awareness and Prevention

Sep 24, 2015

Over the centuries there have been a lot of old-wives tales circulating about eyes and vision. You know, like the one that if someone hits you on the back while your eyes are crossed they will stay that way. Unlike this example, some of these myths do have roots in...

Sep 03, 2015

There are thousands of eye injuries a year related to sports. According to the National Eye Institute eye injuries are the leading cause of blindness in children in North America and most injuries occurring in school-aged children are sports-related. Further 99% of sports-related eye injuries can be prevented simply by...

Aug 30, 2015

The hormonal fluctuations experienced during pregnancy can cause many unexpected changes in your body, including your eyes and vision. Most of these changes are temporary and will return to normal once you give birth. Its important to know which vision changes are normal for an expecting mother and which could...

Aug 16, 2015

A babys visual system develops gradually over the first few months of life. They have to learn to focus and move their eyes, and use them together as a team. The brain also needs to learn how to process the visual information from the eyes to understand and interact with...

Jul 30, 2015

There is a lot more that goes into finding the right pair of sunglasses than just fit and fashion. While its important to look and feel great in your shades, sunglasses also have the very important job of properly protecting your eyes from the sun. Here are a few facts...

Jul 24, 2015

Cataracts are a leading cause of vision loss in the United States and Canada. Here are 6 things you need to know. 1. Chances are you will develop a cataract! Cataracts are considered part of the natural aging process so if you live long enough, you will likely eventually develop...

Jul 21, 2015

Independence Day may have passed but fireworks season is still in full swing and fireworks-related injury and death is a real and serious danger. According to the 2014 Annual Fireworks Report, compiled by the US Consumer Product Safety Commission there were at least 11 deaths and 10,500 injuries due to...

May 29, 2015

Your eyes are constantly at work for you, playing a vital role as you navigate through each day. As May is healthy vision month, here are some things to keep in mind: Know your genes While your eyes may be the same color as your fathers eyes, you may have...

May 17, 2015

According to WomensEyeHealth.org, of blindness and visual impairment occurs in women. Additionally, an estimated 75% of visual impairment is preventable or correctable with proper education and care. With the increased risks for women its critical for women to know about the risks and prevention to effectively protect their eyes...

Apr 30, 2015

Spring is in the air. But along with the beauty of the blooming flowers and budding trees, comes allergy season. The high pollen count and allergens floating in the fresh spring air can certainly wreak havoc on the comfort level of those suffering from allergies, causing an otherwise nature-loving individual...

Mar 31, 2015

Last week, people in South America, Europe, North Africa, and parts of Asia and the Middle East saw a solar eclipse. As you may have heard, looking directly at a solar eclipse is very dangerous for your eyes and vision. Nevertheless, this rare event is something that many people want...

Mar 19, 2015

March is Save Your Vision Month, a time to raise public awareness about how to protect your eyes and your vision. Most people arent aware that 75% of potential vision loss can be prevented or treated. This largely depends on patients being proactive and educated about their eye health. Here...

Mar 11, 2015

Digital devices have impacted our world in so many positive ways, allowing us to connect, work, play and get information at the speed of light. But all of this good brings with it a measure of concern: Digital Eye Strain or Computer Vision Syndrome. Focusing on your vision on digital...

Feb 12, 2015

February is Low Vision and Age-Related Macular Degeneration awareness month. Low vision describes a set of conditions in which there is significant visual impairment which can not be corrected with traditional means such as glasses, contact lenses, medication or eye surgery. Low vision includes a loss of visual acuity...

Jan 27, 2015

January is Glaucoma Awareness Month. Glaucoma is a serious, vision threatening disease. You can save your eyesight, by knowing the facts. Are you at risk of developing glaucoma? The short answer is yes. Anyone can get glaucoma and because of this it is important for every person, young and old...

Dec 31, 2014

Its that time of year againcoughs, sneezing, running noses and itchy, red eyes. How do you know when an eye irritation is something that needs medical attention? First of all, any time an eye infection is accompanied by fever, excessive discharge or pain, you should see your eye doctor immediately....

Dec 22, 2014

One of the most common patient complaints during the winter months is dry eyes. In the cooler climates, cold winds and dry air, coupled with dry indoor heating can be a recipe for eye discomfort. Dryness and irritation can be particularly debilitating for those who wear contact lenses or suffer...

Dec 04, 2014

Winter break is in a few weeksand, with college students finding their way home for the holidays, it is a good time for parents to check in and make sure their independent kids are taking care of themselves properly.Vision plays a key role in learning as well as extra-curricular activities...

Nov 25, 2014

November is Diabetic Eye Disease Awareness Month. Do you know the facts?

Oct 31, 2014

You may have experienced this before. Out of nowhere, your eyelid starts twitching uncontrollably. While this can be a cause of aggravation, eyelid twitches, spasms or tics are actually quite common. Here are 7 things you should know about this eye condition: Eye twitches are generally caused by a repetitive,...

Oct 23, 2014

October is 'Eye Injury Prevention Month' in the USA and 'Eye Health Month' in Canada. There are about 285 million people living with blindness and low vision all around the world. Children account for some 19 million of them. The vast majority of visual impairment is readily treatable and/or preventable....

Sep 28, 2014

The World Sight Day Challenge, slated to take place on October 9, 2014 is an annual awareness day that aims to focus global attention on blindness and vision impairment worldwide. The day aims to create awareness that blindness can be avoided if there is universal access to quality vision and...

Sep 18, 2014

The new school year has kicked off and you can tick off purchasing all that back to school equipment. Now, it's time to think about what your child will need for after school sports and hobby activities. Making sure they have the right protective eyewear for their sporting or athletic...

Aug 27, 2014

A futuristic, yet simplistic, eye implant paired with a smartphone app may change the way eye doctors treat glaucoma.

Aug 24, 2014

School is starting: Do you know how to set up your childs homework and reading spot? Reading and writing are some of the most fundamental skills that your child to facilitate learning in school, so it is important to make sure that your child's eyes are comfortable when they are...

Jul 24, 2014

Summer vacation is well under way, but did you know that even when your child is out of the classroom, vision problems can have an impact on his/her daily activities? Look out for these 4 warning signs during the summer months they could be a sign of vision difficulties...

Jul 17, 2014

Eye floaters are actually more common that you may think. Many people notice specks or cobweb-like images moving around in their line of vision, at some point. Some even report experiencing a "snow globe effect" as if they are swatting at many imaginary bugs. Floaters may be an annoyance, but...

Jun 29, 2014

Cataracts affect millions of people nationwide and as the population continues to age, the numbers keep increasing. The good news is, cataracts are often manageable and treatable. As June is Cataract Awareness Month, here are some facts you should know to help you recognize cataracts and prevent permanent vision loss....

Jun 19, 2014

Have you ever wondered what your eyes do when you finally close them after a long day of visual processing and stimulation? Let's take a closer look at what happens behind your closed lids when your head hits the pillow. Firstly, once your eyes are closed, they do continue to...

May 22, 2014

The heat of long summer days is nearly upon us. As the sun's rays intensify and people spend more time outdoors in the sunshine it is very important to be aware of the potential damage exposure to the sun can have on your eyes. May is UV Awareness month. Here...

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Fox Eye Care Group - Eye Doctor Winston Salem, High Point

Welcome to the Sight Eye Clinic, the premier ophthalmology practice in the Holland and Zeeland area serving all your eye needs! Were glad youre here. We have been members of the West Michigan community since the 1930s, helping our neighbors see clearly and take care of their eyes.

You use your eyes for just about everything in your daily life, yet so many people take them, and their vision, for granted. Poor vision can be life-changing, restricting your independence, taking a toll on your work, interfering with school, and generally impairing your life. For many people, though, it doesnt have to be this way. Active eye care can improve your vision, manage issues like progressive diseases, and help you live a healthier life.

We at Sight Eye work to provide excellent eye care in a warm, compassionate environment in order to serve the community we love. Many of us in our practice share a Christian faith which forms the basis for this mission we are called to love and serve our patients and coworkers as ourselves. To that end, we strive to make Sight Eye a place where anyone in the community feels welcome and receives excellent, personal eye care.

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Ophthalmologist Zeeland, MI | Sight Eye Clinic

Eyesight Ophthalmic Services is southern New Hampshire's leading provider of eye care for both adults and children.

Our skilled staff of ophthalmologists & optometrists can be seen at any of our three convenient locations in Portsmouth, Exeter, and Somersworth. For individual office information, click locations, hours, & directions.

For personal assistance or to schedule an appointment, call 1(888)222-EYES (3937).

Eyesight Ophthalmic Service wasfounded in 1983. We are southern New Hampshire's leading provider of eyecare for adults and children. Specializing in:

- Cataract Surgery & Premium Lens Implants - Macular Degeneration - BOTOX and Eyelid Surgery - Glaucoma - Routine Eyecare - Contact lenses - Designer frames and sunglasses - Low vision rehabilitation - Clinical Research - Diabetic Eye disease - Dry eye treatments - Laser Vision

Our skilled team of doctors will help you make the best decision on your cataract lens choices, whether they are monofocal or premium lenses. We offer a wide range of Premium Lenses including Crystalens, Trulign, Tecnis, and Acrysof Toric. Our doctors will help you determine which lens is best for your lifestyle. We are the only group offering premium intraocular lenses through seacoast area hospitals like Portsmouth Regional Hospital, Exeter Hospital, Frisbie Memorial Hospital and Wentworth Douglass Hospital.

Prepare for your visit and save time in the waiting room, with our downloadable patient forms. Take the time to download our patient forms and fill them out before your visit. Our friendly office staff will be glad to assist you if you have any questions.

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Eyesight NH - Cataract Surgery Portsmouth NH | LASIK Eye ...

An Important Word to Parents

The purpose of this website is to provide parents with fun eye exercises toenhance their childrens visual processing skillsforbetter school performance and sustained attention.If you know a child whostruggles, the underlying cause may be visioneven ifthe childhas 20/20 eyesight. Visual processing skills like tracking, eye teaming, and visual perception are developmentalskills that all children need in addition to seeing clearly. If these skills dont develop normally, children can struggle with demanding visual tasks like reading. Each year as print gets smaller, school performance drops, and as visual fatigue sits in, children become easily frustrated and distracted. All too often, these children appear to have a learning disability or attention problems when the real culprit is poor visual processing skills. Glasses cant help, but eye exercises can! This website will give you good information on vision-based learning problems, and we have even provided you with a great assessment tool to determine if your child is at risk. However, children do not have to have poor vision skills to benefit from these eye exercises. Even children with adequate visual processing can sharpen and improve the learning-related vision skills they already have!

Please Read: The exerciseson this websitearenot vision therapy. Vision therapy is a medical treatment prescribed by developmental optometrists and involves a much wider scope of remediation procedures involving the use oflenses, prisms, filters, and special instruments to train the visual system to work efficiently.Decades of research support the effectiveness of vision therapy to remediate disorders in visual processing. The vision exerciseson this website are designed for visual enhance- ment and are not a substitute for professional care. Like any exer- cise program, we encourage you to check with your eye doctor before beginning. These exercises can improve and sharpen visual skillsimportant for reading, learning, andsustained attention. However, if your childhas difficulty with these activities, it could indicate there is a more significant problem. Talk to your family eye doctor orcontact a developmental optometrist for further evaluation. To locate a doctor in your area, contact the national certifying board for optometrists who specialize in vision therapy at covd.org. It should also be noted that these vision exercises are not meant for children withstrabismus and/or amblyopia.If your child has either condition,do not begin even a simple eye exercise program without the adviceof your eyedoctor.Vision therapy is highly successful in treating both these conditions, butamblyopia and strabismus requirestrictsupervision by a trained professional. Want to learn more about vision-based learning and attention problems?

Go to Eyes CAN Learn.

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Eye Can Learn | Eye Exercises for Visual Health and School ...

Facts about Low Vision Visual Acuity and Low Vision A Functional Definition of Low Vision Low Vision vs. Legal Blindness Visual Impairment Light Perception and Light Projection Total Blindness

Most surveys and studies indicate that the majority of people in the United States with vision loss are adults who are not totally blind; instead, they have what is referred to as low vision. You may have heard the terms "partial sight" or "partial blindness" also used to describe low vision. Those descriptions are no longer in general use, however.

Here is one definition of low vision, related to visual acuity:

Visual acuity is a number that indicates the sharpness or clarity of vision. A visual acuity measurement of 20/70 means that a person with 20/70 vision who is 20 feet from an eye chart sees what a person with unimpaired (or 20/20) vision can see from 70 feet away.

20/70 can best be understood by examining a standard eye testing chart that you may have used in your own doctor's office during an eye examination.

In the United States, the Snellen Eye Chart (pictured left) is a test that ophthalmologists and optometrists use to measure a person's distance visual acuity. It contains rows of letters, numbers, or symbols printed in standardized graded sizes.

Your eye doctor will ask you to read or identify each line or row at a fixed distance (usually 20 feet), although a 10-foot testing distance is also used.

If you can read line 8 (D E F P O T E C) from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision (or visual acuity) as 20/20 with best correction.

If the smallest print you can read is line 3 (T O Z) from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision (or visual acuity) as 20/70 with best correction.

Please note: An actual Snellen Eye Chart is much larger than the one depicted here; therefore, it's not recommended that you use this chart to test your own (or a friend's or family member's) visual acuity.

Not all eye care professionals agree with an exclusively numerical (or visual acuity) description of low vision. Here's another more functional definition of low vision:

"Legal blindness" is a definition used by the United States government to determine eligibility for vocational training, rehabilitation, schooling, disability benefits, low vision devices, and tax exemption programs. It's not a functional low vision definition and doesn't tell us very much at all about what a person can and cannot see.

Part 1 of the U.S. definition of legal blindness states this about visual acuity:

This is a 20/200 visual acuity measurement, correlated with the Snellen Eye Chart (pictured above):

Part 2 of the U.S. definition of legal blindness states this about visual field:

This is a representation of a constricted visual field:

For more information on the definitions of legal blindness, you can read Disability Evaluation Under Social Security, a publication from the Social Security Administration.

Much like low vision, there are many different definitions of visual impairment. "Visual impairment" is a general term that describes a wide range of visual function, from low vision through total blindness.

Here is an example of the variations in the term "visual impairment" or "visually impaired" from the World Health Organization Levels of Visual Impairment:

Moderate Visual Impairment:

Severe Visual Impairment:

Profound Visual Impairment:

Like the term "legal blindness," "visual impairment" is not a functional definition that tells us very much about what a person can and cannot see. It is a classification system, rather than a definition.

These terms describe the ability to perceive the difference between light and dark, or daylight and nighttime. A person can have severely reduced vision and still be able to determine the difference between light and dark, or the general source and direction of a light.

Total blindness is the complete lack of light perception and form perception, and is recorded as "NLP," an abbreviation for "no light perception."

Few people today are totally without sight. In fact, 85% of all individuals with eye disorders have some remaining sight; approximately 15% are totally blind.

Low vision optical devices can make it possible for you to do various tasks, such as reading, doing crafts, and preparing meals. To help you understand the different types of devices and options that are available, see Reading with Low Vision Optical Devices.

Living room image source: From Maureen A. Duffy, Making Life More Livable: Simple Adaptations for Living at Home After Vision Loss (New York, NY: AFB Press, American Foundation for the Blind, 2015), p. 11. 2015 by American Foundation for the Blind. All Rights Reserved.

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Low Vision and Legal Blindness Terms and Descriptions ...

Most Common Adult Vision Problems Most Common Childhood Vision Problems Blurred vision (refractive errors)

These conditions affect the shape of the eye and, in turn, how the eye sees. They can be corrected by eyeglasses, contact lenses, and in some cases surgery.

Strabismus occurs when the eyes do not line up or they are crossed. One eye, however, usually remains straight at any given time. Common forms of strabismus include:

If detected early in life, strabismus can be treated and even reversed.

If left untreated strabismus can cause amblyopia.

Amblyopia often called lazy eye is a problem that is common in children.

Amblyopia is a result of the brain and the eyes not working together. The brain ignores visual information from one eye, which causes problems with vision development.

Treatment for amblyopia works well if the condition is found early. If untreated, amblyopia causes permanent vision loss.

All people with diabetes, both type 1 and type 2, are at risk for DR. It is caused by damage to blood vessels in the back of the eye (retina). The longer someone has diabetes, the more likely he or she will get DR.

People with this condition may not notice any changes to their vision until the damage to the eyes is severe. This is why it is so important for people with diabetes to have a comprehensive eye exam every year.

There are four stages of DR. During the first three stages of DR, treatment is usually not needed. To prevent progression of diabetic retinopathy, people with diabetes should control their levels of blood sugar, blood pressure, and blood cholesterol. For the fourth stage of DR, called proliferative retinopathy, there are treatments that reduce vision loss, but are not a cure for DR.

Warning signs of diabetic retinopathy includes blurred vision, gradual vision loss, floaters, shadows or missing areas of vision, and difficulty seeing at nighttime.

People with diabetes are at greater risk for cataract and glaucoma as well.

Photos courtesy of the National Eye Institute, National Institutes of Health

AMD is a disease that blurs the sharp, central vision needed to see straight-ahead. It affects the part of the eye called the macula that is found in the center of the retina.The macula lets a person see fine detail and is needed for things like reading and driving.

The more common dry form of AMD can be treated in the early stages to delay vision loss and possibly prevent the disease from progressing to the advanced stage. Taking certain vitamins and minerals may reduce the risk of developing advanced AMD.

The less common wet form of AMD may respond to treatment, if diagnosed and treated early.

Photos courtesy of the National Eye Institute, National Institutes of Health

There are different types of glaucoma, but all of them cause vision loss by damaging the optic nerve. Glaucoma is called the sneak thief of sight because people dont usually notice a problem until some vision is lost.

The most common type of glaucoma happens because of slowly increasing fluid pressure inside the eyes.

Vision loss from glaucoma cannot be corrected. But if it is found early, vision loss can be slowed or stopped. A comprehensive eye exam is important so glaucoma can be found early.

Photos courtesy of the National Eye Institute, National Institutes of Health

A cataract is a clouding of the lens of the eye. It often leads to poor vision at night, especially while driving, due to glare from bright lights.

Cataracts are most common in older people, but can also occur in young adults and children.

Cataract treatment is very successful and widely available.

Photos courtesy of the National Eye Institute, National Institutes of Health

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Types of Vision Problems - Department of Health

Human eyesight is a sense which enables animals to perceive the light, different colors, shapes and it serves to the general perception of the environment. It is oriented mainly towards the perception of contrast and thus even contours and it significantly helps with orientation in space. For a human being the eyesight is the most important sense and that is mainly because almost 80% of information from our surroundings is perceived through it.

The human eye (oculus) is the organ of eyesight and is composed of the eye bulb and additional organs. Photosensitive layer is called the retina and contains photoreceptors, highly specialized photosensitive cells, rods and cones thanks to which the image is created. These cells are embedded in the pigmented epithelium which supplies them with nourishment and light isolation.

Vision itself, individual perception of the light, is based on the sensitivity of the eyesight pigments (e.g. rhodopsin) to the light. Under the influence of light the sight pigments decompose and that triggers the cascade chemical reactions which lead to the change of signal into electric potential, impulse, that carries information to the optical centers of the brain.

For the eyesight perception to be perfect we need also parts of the human eye that form its optical system (cornea, vitreous humor, lens, vitreous body) that collects the rays in the way that their focus is on the retina. A defect of optical system causes inability to create a sharp image on the retina and it leads to refractive errors (short-sightedness, long-sightedness, astigmatism).

Human eye equity is the ability to differentiate between two points in space. It depends on the ability of the optical apparatus to concentrate rays on the retina but also depends on the transparency of the human eye, intensity of light and on density and integration of photoreceptors in the given place on the retina.

Ultraviolet rays are the component of sunlight and is divided into UV-A and UV-B and UV-C radiation. UVA rays tan skin and is due to premature skin aging. UV-B rays cause sunburn and are often associated with skin cancer and eye problems such as cataracts. UV-C rays are most dangerous. There are, fortunately, blocked by ozone layer and do not get to the earth's surface.

The color vision is a very complicated psychophysical process during which human eye distinguishes different colors. From the physical point of view the color does not exist and it is only a visual perception which is conditioned by the wavelength of the light. The certain part of the spectrum reflects from different objects, then it falls on the eye where it causes the irritation of the light sensitive elements which react to color the cones. For its realization, it is necessary to have a correct and undisturbed function of the eyesight and the human eye as the receiving organ, the optical path as the transmitting system and the centers of the brain thanks to which we distinguish and thus they are the analyzer of the perception.

When driving a motor vehicle a driver has to continuously monitor not only what is happening on the road but also the data on the panel board. The tilting of his head (in average around 30 degrees) leads to reduction of the sharpness of the image of events happening on the road which is caused by the movement of the eyes. When looking at the speedometer the movement of the eyes exceeds the target by 5 degrees in average and it is immediately balanced with the subsequent movement of the eyes.

If you have uneasiness and it seems to you, that your sight worsen and feeling pain in eyes, you should visit an ophthalmologist. Today, good vision is very important and sight problems should not be ignored, but solved.

Accommodation of the eye is the ability of the human eye to see sharply all objects which are located at various distances in front of the eye depending on the changes of massiveness of the optical system of the eye. The mechanism of eye accommodation is not the same for all animals. For example fish accommodates through the change of position of the lens, some types of birds accommodate through the increase of curvature of the cornea and protraction of the human eye. As far as humans are concerned accommodation is caused by the increased curvature of anterior area of the eye lens while at the same time its thickness also changes. Accommodation is usually the same on both eyes.

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Eyesight and vision - About-Vision.com

Vision therapy: Can we train our sight?

Meghan Dukes

Table of Contents

What is vision therapy?

Who, What, When, and How Long?

What is vision therapy NOT?

Optometrists vs. Ophthalmologists

What does the research say?

Problems with vision therapy

References

The American Optometric Association defines vision therapy (VT) as a treatment plan used to correct or improve specific dysfunctions of the vision system. It includes, but is not limited to, the treatment of strabismus (turned eye), other dysfunctions of binocularity (eye teaming), amblyopic (lazy eye), accommodation (eye focusing), ocular motor function (general eye movement ability), and visual-perception-motor abilities. Optometric vision therapy is based upon a medically necessary plan of treatment which is designed to improve specific vision dysfunctions determined by standardized diagnostic criteria. Treatment plans encompass lenses, prisms, occlusion (eye patching), and other appropriate materials, modalities, and equipment (http://www.children-special-needs.org/vision_therapy/optometric_vision_therapy.html).

Vision therapy, also known as eye exercise, vision training, or orthoptics, (for a definition of these and other vision terms, go to this glossary of terms) is a non-surgical, physical therapy for binocular visual problems; however, vision therapy is not a direct treatment for learning disabilities (http://www.visiontherapy.org/).

Patients of any age can undergo vision therapy, but the treatment varies with each individual based on condition.

Successful vision therapy enhances and improves visual abilities such as fixation, acuity, visual memory, and binocular fusion, to name a few. Treatment plans involve prisms, lenses, computer modalities, and other materials.

The estimated program consists of weekly office visits, along with therapies to be conducted at home.

The treatment requires a great deal of commitment, for it may last for extensive periods of time depending on the individual. However, research has shown that the improvements due to vision therapy continue post-treatment (http://www.children-special-needs.org/questions_pf.html).

Further information regarding the dynamics of vision therapy may be located here.

It is important not to confuse optometric vision therapy with holistic practices such as the Bates Method, integrated vision therapy, or natural eye exercises. There is no scientific research or results that indicate these methods are valid; however, the internet is swarming with advertisements and descriptions of products that claim otherwise (http://www.vision-therapy.com).

The See Clearly Method is a series of daily eye exercises that claim to naturally reduce the need for glasses or contact lenses by toning and relaxing your eye muscles and relieving stress that hampers clear vision (http://www.seeclearlymethod.com/content/see clear.html).

A similar program called Vision for Life provides daily optical exercises that claim to stimulate and strengthen the muscles of the eye, resulting in improved vision and decreasing the dependency on glasses or contact lenses. Through testimonials, quotes, and flashy pictures, the Vision for Life website attempts to promote their method of natural vision improvement (http://www.rebuildyourvision.com).

Yoga is another branch of holistic therapy for vision. Yoga exercises claim to stretch, relax, and tone the optical nerves, which improves eyesight and alleviates tension, irritability, and itchiness of the eyes (http://www.indolink.com/Vasantha/eyeYoga.html).

The Bates Method is a psychosomatic approach to vision impairment. Without using strengthening exercises for the eye muscles, the Bates Method claims to improve visual clarity through relaxation exercises (http://www.seeing.org).

Several examples of holistic eye exercises can be found at Holistic-online.

An optometrist is licensed by the state to provide primary eye care, while an ophthalmologist is a physician of osteopathy who specializes in prevention of eye disease, eye care, and the visual system. The ophthalmologist is medically trained and licensed in all eye care, and is not trained in vision therapy.

Thus, support of vision therapy in the United States mainly comes from optometrists. Vision therapy saw its beginnings in the late 1800s in orthoptics, which is the science of correcting binocular vision impairments, and is now a form of vision therapy (http://www.vision-therapy.com/Glossary_of_Terms.htm). Present day ophthalmologists, for the most part, do not support vision therapy, and it has been speculated that this is due to the fact that they are trained to use drugs and surgery to treat eye dysfunction (http://www.children-special-needs.org/questions_pf.html).

There have been several concerns regarding the reliability and validity of the research surrounding the efficacy of vision therapy (http://members.aol.com/scottolitsky/vt.htm).

The sample population is not random, there are small numbers of patients in each study, and the results cannot be generalized because it does not reflect the population

Research that shows support of vision therapy have conflicts of interest in proving the

validity of vision therapy

There are many definitions of vision therapy found on the internet and in research studies. Thus, most of the data cannot be compared or generalized because vision therapy is defined differently (Coffey, B., Wick, B., Cotter, S., Scharre, J., & Horner, D., 1992).

Eye exercises, lenses, and perceptual training have not been scientifically proven to be useful. In addition, the problems that they intend to treat have never been proven to cause a learning disability.

As well, the American Academy of Ophthalmology and the American Academy of

Pediatrics made this statement regarding vision therapy:

No scientific evidence supports claims that the academic abilities of children with learning disabilities can be improved with treatments that are based on 1) visual training, including muscle exercises, ocular pursuit, tracking exercises, or 'training' glasses (with or without bifocals or prisms), 2) neurologic organizational training (laterality training, crawling, balance board, perceptual training), or 3) colored lenses. These more controversial methods of treatment may give parents and teachers a false sense of security that a child's reading difficulties are being addressed, which may delay proper instruction or remediation. The expense of these methods is unwarranted, and they cannot be substituted for appropriate educational measures. Claims of improved reading ... are almost always based on poorly controlled studies that typically rely on anecdotal information. These methods are without scientific validation. Their reported benefits can be explained by the traditional educational remedial techniques with which they are usually combined. (http://www.allaboutvision.com/parents/vision_therapy.htm)

A study by Adler (2002) concluded that vision therapy is an effective treatment for convergence insufficiency. The restoration of near point of convergence values to normal accompanied by a reduction in symptoms was concluded as successful treatment. Routine eye exercises were shown to have a highly significant (t = 14.61, p < 0.001) effect. Although treatment times were longer, the rate of success was greater than that reported by previous studies. As well, Verma & Singh (1997) reported that active visual therapy improved visual impairments in amblyopic children and young adults. The study used various methods of therapy on 160 patients, ranging from 3.5 to 25 years of age, who had lens implants, and visual acuity improved in the majority of the patients.

However, research surrounding the effects of visual therapy on learning disabilities has had mixed results. Having a visual impairment does not result in a learning disability, nor does the treatment of the impairment cure the disability. In fact, according to this study, there has been no scientific evidence for the efficacy of eye exercises in the elimination of the learning difficulties (Learning disabilities, dyslexia, and vision: a subject review, 1998). Vision therapy does not claim to directly treat the learning disability; however, it is an indirect influence, for it treats the visual impairments that influence reading and learning (http://www.visiontherapy.org). Research by Simons & Grisham (1987) supports a relationship between particular binocular disorders and reading problems. From these results, it can be hypothesized that if binocular disorders are alleviated, the reading disability, due to the positive correlation, will be less severe (Simons & Grisham, 1987).

Further research studies on the effects of vision therapy for eye disorders:

Accomodative Disorders (eye focusing problems)

Binocularity Dysfunctions (eye teaming problems)

Ocular Motility Dysfunctions (eye tracking problems

Strabismus (turned eye)

Amblyopic (lazy eye)

Adler, P. (2002). Efficacy of treatment for convergence insufficiency using vision therapy. Ophthalmic and Physiological Optics, 22, 565-571.

Cirigliano, Suzette. Glossary of Vision Terms. http://www.vision-therapy.com/Glossary_of_Terms.htm 9/22/2003

Cirigliano, Suzette. (2003). Research studies about vision therapy treatment. http://www.vision-therapy.com/vt_research_studies.htm 9/22/2003

Coffey, B., Wick, B., Cotter, S., Scharre, J., & Horner, D. (1992). Treatment options in intermittent exotropia: a critical appraisal. Optometry of Visual Science, 69, 386-404.

Glackin, Stella. (1990). The office eye workout; heres how to ensure that your VDT doesnt come to stand for Vision Destroying Terminal. East West, 20, 60.

http://members.aol.com/scottolitsky/vt.htm 9/22/2003

http://www.allaboutvision.com/parents/vision_therapy.htm 9/22/2003

http://www.indolink.com/Vasantha/eyeYoga.html 9/22/2003

http://www.seeclearlymethod.com 9/22/2003

http://www.seeing.org 9/22/2003

Learning disabilities, dyslexia, and vision: a subject review. (1998). Pediatrics, 102, 1217.

Optometrists Network. http://www.children-special-needs.org/questions_pf.html 9/22/2003

Press, L. J. Vision therapy FAQs. http://www.visiontherapy.org/vision-therapy/faqs/vision-therapy-FAQs.html 9/22/2003

Rouse, M. W. (1987). Management of binocular anomalies: efficacy of vision therapy in the treatment of accommodative deficiencies. American Journal of Physiological Optometry, 64, 415-420.

Simons, H. D., & Grisham, J.D. (1987). Binocular anomalies and reading problems. Journal of American Optometry Association, 58, 578-87.

Toufexis, A. (1989). Workouts for the eyes; therapies to improve visual performance get mixed reviews. Time, 133, 86.

Verma, A., & Singh, D. (1997). Active vision therapy for pseudophakic amblyopic. Journal of Cataract and Refractive Surgery, 23, 1089-1094.

Vision for life. (2002). Our program for rebuilding your vision naturally. http://www.rebuildyourvision.com/our_program.htm 9/22/2003

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Vision Therapy: Can We Train Our Sight (Vanderbilt.edu)

By Gary Heiting, OD

Refractive errors often are the main reason a person seeks the services of an optometrist or ophthalmologist. But what does it really mean when we're told that our vision is blurry because we have a refractive error?

We see the world around us because of the way our eyes bend (refract) light. Refractive errors are optical imperfections that prevent the eye from properly focusing light, causing blurred vision. The primary refractive errors are nearsightedness, farsightedness and astigmatism.

Refractive errors usually can be "corrected" with eyeglasses or contact lenses, or they can be permanently treated with LASIK and other vision correction surgery (also called refractive surgery).

In order to see, we must have light. While we don't fully understand all the different properties of light, we do have an idea of how light travels.

A light ray can be deflected, reflected, bent or absorbed, depending on the different substances it encounters.

When light travels through water or a lens, for example, its path is bent or refracted. Certain eye structures have refractive properties similar to water or lenses and can bend light rays into a precise point of focus essential for sharp vision.

Most refraction in the eye occurs when light rays travel through the curved, clear front surface of the eye (cornea). The eye's natural (crystalline) lens also bends light rays. Even the eye's tear film and internal fluids (aqueous humor and vitreous) have refractive abilities.

The process of vision begins when light rays that reflect off objects and travel through the eye's optical system are refracted and focused into a point of sharp focus.

For good vision, this focus point must be on the retina. The retina is the tissue that lines the inside of the back of the eye, where light-sensitive cells (photoreceptors) capture images in much the same way that film in a camera does when exposed to light. These images then are transmitted through the eye's optic nerve to the brain for interpretation.

Just as a camera's aperture (called the diaphragm) is used to adjust the amount of light needed to expose film in just the right way, the eye's pupil widens or constricts to control the amount of light that reaches the retina.

In dark conditions, the pupil widens. In bright conditions, the pupil constricts.

The eye's ability to refract or focus light sharply on the retina primarily is based on three eye anatomy features: 1) the overall length of the eye, 2) the curvature of the cornea and 3) the curvature of the lens inside the eye.

More obscure vision errors, known as higher-order aberrations, also are related to flaws in the way light rays are refracted as they travel through the eye's optical system.

These types of vision errors, which can create problems such as poor contrast sensitivity, are detected through new technology known as wavefront analysis.

Your eye doctor determines the type and degree of refractive error you have by performing a test called a refraction.

This can be be done with a computerized instrument (automated refraction) or with a mechanical instrument called a phoropter that allows your eye doctor to show you one lens at a time (manual refraction).

Often, an automated refraction will be performed by a member of the doctor's staff, and then the eye care practitioner will refine and verify the results with a manual refraction.

Your refraction may reveal that you have more than one type of refractive error. For example, your blurred vision may be due to both nearsighted and astigmatism.

Your eye doctor will use the results of your refraction to determine your eyeglasses prescription. A refraction, however, does not provide sufficient information to write a contact lens prescription, which requires a contact lens fitting.

Eyeglass lenses and contact lenses are fabricated with precise curves to refract light to the degree necessary to compensate for refractive errors and bring light to a sharp focus on the retina.

Vision correction surgeries such as LASIK aim to correct refractive errors by changing the shape of the cornea, so that light rays are bent into a more accurate point of focus.

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About the Author: Gary Heiting, OD, is senior editor of AllAboutVision.com. Dr. Heiting has more than 25 years of experience as an eye care provider, health educator and consultant to the eyewear industry. His special interests include contact lenses, nutrition and preventive vision care. Connect with Dr. Heiting via Google+.

Marilyn Haddrill and Charles Slonim, MD, also contributed to this article.

[Page updated March 2015]

Link:
Refractive Errors and Refraction - How the Eye Sees

Points toRemember

Diabetic eye disease can affect many parts of the eye, including the retina, macula, lens and the optic nerve.

Diabetic eye disease is a group of eye conditions that can affect people with diabetes.

Diabetic eye disease also includes cataract and glaucoma:

All forms of diabetic eye disease have the potential to cause severe vision loss and blindness.

Chronically high blood sugar from diabetes is associated with damage to the tiny blood vessels in the retina, leading to diabetic retinopathy. The retina detects light and converts it to signals sent through the optic nerve to the brain. Diabetic retinopathy can cause blood vessels in the retina to leak fluid or hemorrhage (bleed), distorting vision. In its most advanced stage, new abnormal blood vessels proliferate (increase in number) on the surface of the retina, which can lead to scarring and cell loss in the retina.

Diabetic retinopathy may progress through four stages:

DME is the build-up of fluid (edema) in a region of the retina called the macula. The macula is important for the sharp, straight-ahead vision that is used for reading, recognizing faces, and driving. DME is the most common cause of vision loss among people with diabetic retinopathy. About half of all people with diabetic retinopathy will develop DME. Although it is more likely to occur as diabetic retinopathy worsens, DME can happen at any stage of the disease.

People with all types of diabetes (type 1, type 2, and gestational) are at risk for diabetic retinopathy. Risk increases the longer a person has diabetes. Between 40 and 45 percent of Americans diagnosed with diabetes have some stage of diabetic retinopathy, although only about half are aware of it. Women who develop or have diabetes during pregnancy may have rapid onset or worsening of diabetic retinopathy.

The same scene as viewed by a person normal vision (Top) and with (Center) advanced diabetic retinopathy. The floating spots are hemorrhages that require prompt treatment. DME (Bottom) causes blurred vision.

The early stages of diabetic retinopathy usually have no symptoms. The disease often progresses unnoticed until it affects vision. Bleeding from abnormal retinal blood vessels can cause the appearance of floating spots. These spots sometimes clear on their own. But without prompt treatment, bleeding often recurs, increasing the risk of permanent vision loss. If DME occurs, it can cause blurred vision.

Diabetic retinopathy and DME are detected during a comprehensive dilated eye exam that includes:

A comprehensive dilated eye exam allows the doctor to check the retina for:

If DME or severe diabetic retinopathy is suspected, a fluorescein angiogram may be used to look for damaged or leaky blood vessels. In this test, a fluorescent dye is injected into the bloodstream, often into an arm vein. Pictures of the retinal blood vessels are taken as the dye reaches the eye.

Vision lost to diabetic retinopathy is sometimes irreversible. However, early detection and treatment can reduce the risk of blindness by 95 percent. Because diabetic retinopathy often lacks early symptoms, people with diabetes should get a comprehensive dilated eye exam at least once a year. People with diabetic retinopathy may need eye exams more frequently. Women with diabetes who become pregnant should have a comprehensive dilated eye exam as soon as possible. Additional exams during pregnancy may be needed.

Studies such as the Diabetes Control and Complications Trial (DCCT) have shown that controlling diabetes slows the onset and worsening of diabetic retinopathy. DCCT study participants who kept their blood glucose level as close to normal as possible were significantly less likely than those without optimal glucose control to develop diabetic retinopathy, as well as kidney and nerve diseases. Other trials have shown that controlling elevated blood pressure and cholesterol can reduce the risk of vision loss among people with diabetes.

Treatment for diabetic retinopathy is often delayed until it starts to progress to PDR, or when DME occurs. Comprehensive dilated eye exams are needed more frequently as diabetic retinopathy becomes more severe. People with severe nonproliferative diabetic retinopathy have a high risk of developing PDR and may need a comprehensive dilated eye exam as often as every 2 to 4 months.

DME can be treated with several therapies that may be used alone or in combination.

Anti-VEGF Injection Therapy. Anti-VEGF drugs are injected into the vitreous gel to block a protein called vascular endothelial growth factor (VEGF), which can stimulate abnormal blood vessels to grow and leak fluid. Blocking VEGF can reverse abnormal blood vessel growth and decrease fluid in the retina. Available anti-VEGF drugs include Avastin (bevacizumab), Lucentis (ranibizumab), and Eylea (aflibercept). Lucentis and Eylea are approved by the U.S. Food and Drug Administration (FDA) for treating DME. Avastin was approved by the FDA to treat cancer, but is commonly used to treat eye conditions, including DME.

The NEI-sponsored Diabetic Retinopathy Clinical Research Network compared Avastin, Lucentis, and Eylea in a clinical trial. The study found all three drugs to be safe and effective for treating most people with DME. Patients who started the trial with 20/40 or better vision experienced similar improvements in vision no matter which of the three drugs they were given. However, patients who started the trial with 20/50 or worse vision had greater improvements in vision with Eylea.

Most people require monthly anti-VEGF injections for the first six months of treatment. Thereafter, injections are needed less often: typically three to four during the second six months of treatment, about four during the second year of treatment, two in the third year, one in the fourth year, and none in the fifth year. Dilated eye exams may be needed less often as the disease stabilizes.

Avastin, Lucentis, and Eylea vary in cost and in how often they need to be injected, so patients may wish to discuss these issues with an eye care professional.

The retina of a person with diabetic retinopathy and DME, as viewed by optical coherence tomography (OCT). The two images were taken before (Top) and after anti-VEGF treatment (Bottom). The dip in the retina is the fovea, a region of the macula where vision is normally at its sharpest. Note the swelling of the macula and elevation of the fovea before treatment.

Focal/grid macular laser surgery. In focal/grid macular laser surgery, a few to hundreds of small laser burns are made to leaking blood vessels in areas of edema near the center of the macula. Laser burns for DME slow the leakage of fluid, reducing swelling in the retina. The procedure is usually completed in one session, but some people may need more than one treatment. Focal/grid laser is sometimes applied before anti-VEGF injections, sometimes on the same day or a few days after an anti-VEGF injection, and sometimes only when DME fails to improve adequately after six months of anti-VEGF therapy.

Corticosteroids. Corticosteroids, either injected or implanted into the eye, may be used alone or in combination with other drugs or laser surgery to treat DME. The Ozurdex (dexamethasone) implant is for short-term use, while the Iluvien (fluocinolone acetonide) implant is longer lasting. Both are biodegradable and release a sustained dose of corticosteroids to suppress DME. Corticosteroid use in the eye increases the risk of cataract and glaucoma. DME patients who use corticosteroids should be monitored for increased pressure in the eye and glaucoma.

For decades, PDR has been treated with scatter laser surgery, sometimes called panretinal laser surgery or panretinal photocoagulation. Treatment involves making 1,000 to 2,000 tiny laser burns in areas of the retina away from the macula. These laser burns are intended to cause abnormal blood vessels to shrink. Although treatment can be completed in one session, two or more sessions are sometimes required. While it can preserve central vision, scatter laser surgery may cause some loss of side (peripheral), color, and night vision. Scatter laser surgery works best before new, fragile blood vessels have started to bleed. Recent studies have shown that anti-VEGF treatment not only is effective for treating DME, but is also effective for slowing progression of diabetic retinopathy, including PDR, so anti-VEGF is increasingly used as a first-line treatment for PDR.

A vitrectomy is the surgical removal of the vitreous gel in the center of the eye. The procedure is used to treat severe bleeding into the vitreous, and is performed under local or general anesthesia. Ports (temporary water-tight openings) are placed in the eye to allow the surgeon to insert and remove instruments, such as a tiny light or a small vacuum called a vitrector. A clear salt solution is gently pumped into the eye through one of the ports to maintain eye pressure during surgery and to replace the removed vitreous. The same instruments used during vitrectomy also may be used to remove scar tissue or to repair a detached retina.

Vitrectomy may be performed as an outpatient procedure or as an inpatient procedure, usually requiring a single overnight stay in the hospital. After treatment, the eye may be covered with a patch for days to weeks and may be red and sore. Drops may be applied to the eye to reduce inflammation and the risk of infection. If both eyes require vitrectomy, the second eye usually will be treated after the first eye has recovered.

An eye care professional can help locate and make referrals to low vision and rehabilitation services and suggest devices that may help make the most of remaining vision. Many community organizations and agencies offer information about low vision counseling, training, and other special services for people with visual impairment. A nearby school of medicine or optometry also may provide low vision and rehabilitation services.

The NEI is conducting and supporting research that seeks better ways to detect, treat, and prevent vision loss in people with diabetes. This research is being conducted in labs and clinical centers across the country.

For example, the Diabetic Retinopathy Clinical Research Network (DRCR.net) conducts large multi-center trials to test new therapies for diabetic eye disease, and to compare different therapies. The network formed in 2002 and comprises more than 350 physicians practicing at more than 140 clinical sites across the country. Many of the sites are private practice eye clinics, enabling the network to quickly bring innovative treatments from research into community practice.

NEI-funded scientists are also seeking ways to detect diabetic retinopathy at earlier stages. For example, researchers are harnessing a technology called adaptive optics (AO) to improve imaging techniques such as OCT. AO was developed by astronomers seeking to improve the resolution of their telescopes by filtering out distortions in the atmosphere. In the clinic, diagnostic devices that use AO may improve the detection of subtle changes in retinal tissue and bloodvessels.

Go here to see the original:
Facts About Diabetic Eye Disease | National Eye Institute

By Gary Heiting, OD

Protecting your eyesight is one of the most important things you can do to help maintain your quality of life. Some type of sight-threatening eye problem affects one in six adults age 45 and older. And the risk for vision loss only increases with age.

In fact, a recent American Academy of Ophthalmology (AAO) report estimates that more than 43 million Americans will develop age-related eye diseases by 2020. Since the leading causes of blindness and low vision in the United States are primarily age-related diseases such as macular degeneration, cataract, diabetic retinopathy and glaucoma, protecting your eyesight as you age is an essential part of your health care.

To protect your eyesight and keep your eyes healthy as you age, consider these simple guidelines:

Studies also have shown that eating fish rich in omega-3 fatty acids may reduce your risk of developing macular degeneration. Also, consider supplementing your diet with eye vitamins to make sure you are getting adequate amounts of the nutrients you need to keep your eyes healthy.

In addition to following these guidelines, be sure to wear safety glasses when working with tools or participating in active sports to help prevent eye injuries that potentially could cause permanent vision loss.

It's true that following these steps is no guarantee of perfect vision throughout your lifetime. But maintaining a healthy lifestyle and having regular eye exams will certainly decrease your risk of developing a sight-stealing eye problem that otherwise might have been prevented.

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About the Author: Gary Heiting, OD, is senior editor of AllAboutVision.com. Dr. Heiting has more than 25 years of experience as an eye care provider, health educator and consultant to the eyewear industry. His special interests include contact lenses, nutrition and preventive vision care. Connect with Dr. Heiting via Google+.

[Page updated February 2016]

Read more:
Eight Ways to Protect Your Eyesight - AllAboutVision.com

Do you spend more than 2 hours in a day working on a computer? Do your eyes feel tired in the evening after working on a computer screen? Do you occasionally suffer from blurred vision or stiff neck and shoulder pains? If your answer is yes to any of the two questions, you are not alone. Like million others, you too may be suffering from the Computer Vision Syndrome (CVS) or eye strain.

Computer vision syndrome or CVS is the straining of the eyes which occurs when a person uses computer/laptop for continuous and prolonged periods of time. It is usually a temporary discomfort which fades away on its own, however if the discomfort continues to linger or worsens, one needs to follow simple day to day practices to minimize it. More than half of the people who work on computers have at least some symptoms related to eye strain problems. Nowadays even children are suffering through these issues due to continuous usage of video games, mobile phones and television.

What causes Computer Vision Syndrome?

How to avoid Computer Vision Syndrome?

1. Use proper lighting. Put shades and drapes on windows to avoid bright light coming from outside, when you are working on a computer.

2. Adjust the brightness of your computer screen. Closely match the brightness of the environment with that of your computer screen, by using the buttons on the monitor.

3. Reduce glare. Install an anti-glare screen on your monitor. Again, when outside light cannot be reduced, use a computer hood. Have an anti-reflective coating applied to your glasses. This will prevent glare and reflections on the backside of your lenses from reaching your eyes.

4. Take frequent breaks. Avoid working on computer screen for long hours. Do phone calls, or get up for a glass of water, chat with a colleague to relieve eye strain.

5. Follow 20-20-20 rule. Take a 20 second break and look 20 feet away every 20 minutes. This exercise will help you prevent strained near vision and stretch your focusing muscles.

6. Remember to blink as it rewets the eyes.

7. Exercise even when sitting. Anyone in a sedentary job, especially those using computers, should stand up, move about, or exercise their arms, legs, back, neck, and shoulders frequently.

While these measures will resolve Computer Vision Syndrome, in many cases it is recommended to visit an eye specialist for consultation whenever the above symptoms are observed.

Read this article:
Computer Vision Syndrome | Eye Treatment - Centre For Sight

The most common vision problems are refractive errors, more commonly known as nearsightedness, farsightedness, astigmatism and presbyopia. Refractive errors occur when the shape of the eye prevents light from focusing directly on the retina. The length of the eyeball (either longer or shorter), changes in the shape of the cornea, or aging of the lens can cause refractive errors. Most people have one or more of theseconditions.

The cornea and lens bend (refract) incoming light rays so they focus precisely on the retina at the back of theeye.

Refraction is the bending of light as it passes through one object to another. Vision occurs when light rays are bent (refracted) as they pass through the cornea and the lens. The light is then focused on the retina. The retina converts the light-rays into messages that are sent through the optic nerve to the brain. The brain interprets these messages into the images wesee.

The most common types of refractive errors are nearsightedness, farsightedness, astigmatism andpresbyopia.

Nearsightedness (also called myopia) is a condition where objects up close appear clearly, while objects far away appear blurry. With nearsightedness, light comes to focus in front of the retina instead of on the retina. Learn more about nearsightedness.

Farsightedness (also called hyperopia) is a common type of refractive error where distant objects may be seen more clearly than objects that are near. However, people experience farsightedness differently. Some people may not notice any problems with their vision, especially when they are young. For people with significant farsightedness, vision can be blurry for objects at any distance, near or far. Learn more about farsightedness.

Astigmatism is a condition in which the eye does not focus light evenly onto the retina, the light-sensitive tissue at the back of the eye. This can cause images to appear blurry and stretched out. Learn more about astigmatism.

Presbyopia is an age-related condition in which the ability to focus up close becomes more difficult. As the eye ages, the lens can no longer change shape enough to allow the eye to focus close objects clearly. Learn more about presbyopia.

Presbyopia affects most adults over age 35. Other refractive errors can affect both children and adults. Individuals that have parents with certain refractive errors may be more likely to get one or more refractiveerrors.

Blurred vision is the most common symptom of refractive errors. Other symptoms mayinclude:

An eye care professional can diagnose refractive errors during a comprehensive dilated eye examination. People with a refractive error often visit their eye care professional with complaints of visual discomfort or blurred vision. However, some people dont know they arent seeing as clearly as theycould.

Refractive errors can be corrected with eyeglasses, contact lenses, orsurgery.

Follow this link:
Common vision problems | National Eye Institute

Approximately 12 million Americans suffer from a disease called dry eye syndrome. Dry eye syndrome is a chronic lack of sufficient lubrication and moisture in the eye. Its consequences range from subtle but consistent irritation to ocular inflammation of the anterior tissues of the eye. The condition is one of the most common disorders among people over 40. In fact, 20% of all adults have some degree of dry eye syndrome and women past menopause are especially susceptible.

For some people, the stinging, burning and redness may seem like little more than a nuisance. But, if left untreated, dry eye syndrome can lead to serious eye problems, including blindness. Dry eyes are inflamed eyes. Inflammation of the front surface of the eye increases the risk of infection and can also lead to scarring. Once scarring occurs, permanent loss of sight can occur.

Understanding Dry Eye Syndrome

Tears are essential for good eye health, bathing the eye, washing out dust and debris while keeping the eye moist. The eyes produce two types of tears lubricating and reflex tears. Lubricating tears are composed of three layers which coat the eye with mucus and contain water, proteins and oil to protect the eye and prevent evaporation of the aqueous layer. Reflex tears are produced in response to eye injury or irritation.

With dry eye syndrome, the eye does not produce enough tears or the tears have a chemical composition that causes them to evaporate too quickly. The cause of dry eye syndrome is a dysfunction of the tear-producing glands which results in reduced production of tears. It can occur as a part of the natural aging process, especially during menopause or as a side effect of many medications such as antihistamines, anti-depressants, diuretics, certain blood pressure medications, Parkinsons medication and birth control pills.

Dry eye syndrome can be aggravated if you live in a dry, dusty or windy climate. Air conditioning and dry heating systems can dry out your eyes as well. Insufficient blinking, such as when you are staring at a computer screen all day can contribute to it as well.

Recent research indicates that contact lens wear and dry eyes can be a vicious cycle. Dry eyes are the most common complaint among contact lens wearers. Dry eye syndrome results in contact lens discomfort and the rubbing of the lens against the conjunctiva seem to be a cause of dry eyes.

Dry eye syndrome is common in women, possibly due to hormonal fluctuations. Recent research suggests that smoking, too, can increase your risk of dry eye syndrome.

Dry eyes are also a symptom of systemic diseases such as lupus, rheumatoid arthritis, Rosacea or Sjorgrens syndrome.

Signs and Symptoms of Dry Eye Syndrome

Persistent dryness, scratching and burning in your eyes are signs of dry eye syndrome. These symptoms alone may be enough to diagnose dry eye syndrome. Sometimes, the amount of tears in your eyes is measured, using a Schirmer test. This is done by placing a thin strip of filter paper at the edge of the eye. Some people also experience a foreign body sensation the feeling that something is in the eye.

Center For Sight is a leader in bringing our patients the latest advances for the care of dry eye syndrome. Today, there are more treatment options than ever that can help to reduce or eliminate the symptoms, depending on the dryness of your eyes.

Artificial Tears

The simplest approach to treating dry eyes is to supplement your bodys natural tears with lubricating artificial tears. We recommend using mildly preserved brands such as Tears Plus, Refresh, Systane, Soothe or their preservative free counterparts, as well as Bion Tears or TheraTears.

Nutritional Supplementation

Studies have shown that Vitamin A deficiency is linked to dry eye syndrome. Your doctor might suggest a specific formulation, such as TheraTears Nutrition or BioTears.

Medications

Dry eye syndrome has been shown to be an inflammatory eye disorder and your doctor might prescribe anti-inflammatory medicines such as Restasis (eye drops used twice daily) or Lotemax (your doctor will prescribe the frequency of use).

Environmental Control

You may be able to significantly ease the discomfort of dry eye syndrome by reducing factors in your environment that contribute to the problem. Maintaining humidity, avoiding the use of ceiling fans and looking away from the computer or television screen every ten minutes are all helpful. Also, try to blink more frequently to spread tears over the eyes.

Tear Duct Inserts

The eyes lubricating balance is maintained by its volume and quality of tears produced by certain glands, and excess tears are drained into the nose and throat through tear ducts located in each eyelid. If the drain is working too well, the eyes natural moisture can be lost, resulting in a dry eye. Your doctor might elect to insert a temporary (collagen) or permanent (silicone or thermoacrylic) stopper to plug the drainage, allowing your own tears to bathe your eyes for a longer period. They are inserted in a painless in-office procedure and may be removed at any time.

Make the Clear Choice

Our physicians examine and treat eye disorders and diseases and coordinate all post-operative care. They provide 24 hour/7 days a week emergency care to all our patients.

Click here to request an appointment with a Center For Sight optometric physician or call the location nearest to you.

University Park 351-9440 Sarasota US 41 925-2020 Sarasota Siesta Dr. 953-2020 Sarasota - Fruitville 923-4594 Venice 488-2020 Englewood 474-2020 North Port 484-2020

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Dry Eye and Dry Eye Syndrome - Center for Sight in ...

LASIK is a surgical procedure for correcting near sightedness(myopia), far sightedness(hyperopia) and cylindrical(astigmatic) refractive errors. LASIK stands for Laser-Assisted in Situ Keratomileusis.

Have you been thinking of laser vision correction? Shed your doubts, concerns, specs and contact lenses, because blade free LASIK has arrived. With this technology, laser vision correction procedure has become 100 percent blade-free and completely safe.

In any LASIK procedure the first step is to create a corneal flap. In standard LASIK the surgeon uses a hand-held oscillating blade called microkeratome to cut the corneal flap. The flap is then folded and the Excimer laser treats the cornea to correct the refractive error.

In blade free LASIK, femtosecond laser has replaced the steel blade for creation of the corneal flap which improves visual outcome and post-operative comfort for the patient.

When you opt for advanced blade free LASIK procedure you get a completely integrated, personalized vision correction procedure based on cutting edge technology at every step. NASA recommends blade free LASIK to aspiring astronauts to get rid of their specs, as it can withstand high gravitational forces and has been found to be stable and secure even in extreme environmental conditions.

Advantages

For people with nearsightedness (myopia), farsightedness (hyperopia) or astigmatism, LASIK surgery could be the key to a life free of bulky spectacles or contact lenses. But not everybody is a suitable candidate for this type of laser eye surgery. Here are the few main questions a LASIK surgeon is likely to ask you during a consultation.

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Lasik eye surgery - Centre For Sight

The Importance of Nutrition

Researchers have linked eye-friendly nutrients such as lutein/zeaxanthin, vitamin C, vitamin E, and zinc to reducing the risk of certain eye diseases, including macular degeneration and cataract formation. For more information on the importance of good nutrition and eye health, please see the diet and nutrition section.

Acanthamoeba is one of the most ubiquitous organisms in the environment, but rarely causes infections. When infection does occur, however, it can be extremely serious and vision threatening. Recently, there have been multiple reports of increasing incidence of Acanthamoeba keratitis. Co-infection with a bacterial keratitis is common both in the contact lens case and on the cornea, complicating prevention, diagnosis and treatment.

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Lazy eye, or amblyopia, is the loss or lack of development of central vision in one eye that is unrelated to any eye health problem and is not correctable with lenses. It can result from a failure to use both eyes together. Lazy eye is often associated with crossed-eyes or a large difference in the degree of nearsightedness or farsightedness between the two eyes. It usually develops before age six and it does not affect side vision.

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Anterior uveitis is an inflammation of the middle layer of the eye, which includes the iris (colored part of the eye) and adjacent tissue, known as the ciliary body. If untreated, it can cause permanent damage and loss of vision from the development of glaucoma, cataract or retinal edema. It usually responds well to treatment; however, there may be a tendency for the condition to recur.

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Astigmatism is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye.

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Blepharitis is an inflammation of the eyelids and eyelashes causing red, irritated, itchy eyelids and the formation of dandruff like scales on eyelashes.

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A cataract is a cloudy or opaque area in the normally clear lens of the eye. Depending upon its size and location, it can interfere with normal vision. Most cataracts develop in people over age 55, but they occasionally occur in infants and young children. Usually cataracts develop in both eyes, but one may be worse than the other.

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A chalazion is a slowly developing lump that forms due to blockage and swelling of an oil gland in the eyelid. It is more common in adults than children and occurs most frequently in persons 30 to 50 years of age.

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Color vision deficiency is the inability to distinguish certain shades of color or in more severe cases, see colors at all. The term "color blindness" is also used to describe this visual condition, but very few people are completely color blind.

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Conjunctivitis is an inflammation of the conjunctiva, the thin, transparent layer that lines the inner eyelid and covers the white part of the eye.

The three main types of conjunctivitis are infectious, allergic and chemical. The infectious type, commonly called "pink eye" is caused by a contagious virus or bacteria.

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Diabetes is a disease that interferes with the body's ability to use and store sugar and can cause many health problems. One, called diabetic retinopathy, can weaken and cause changes in the small blood vessels that nourish your eye's retina, the delicate, light sensitive lining of the back of the eye. These blood vessels may begin to leak, swell or develop brush-like branches.

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The tears your eyes produce are necessary for overall eye health and clear vision. Dry eye means that your eyes do not produce enough tears or that you produce tears which do not have the proper chemical composition.

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Eye coordination is the ability of both eyes to work together as a team. Each of your eyes sees a slightly different image and your brain, by a process called fusion, blends these two images into one three-dimensional picture. Good eye coordination keeps the eyes in proper alignment. Poor eye coordination results from a lack of adequate vision development or improperly developed eye muscle control.

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Glaucoma is an eye disease in which the internal pressure in your eyes increases enough to damage the nerve fibers in your optic nerve and cause vision loss. The increase in pressure happens when the passages that normally allow fluid in your eyes to drain become clogged or blocked. The reasons that the passages become blocked are not known.

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Farsightedness, or hyperopia, as it is medically termed, is a vision condition in which distant objects are usually seen clearly, but close ones do not come into proper focus. Farsightedness occurs if your eyeball is too short or the cornea has too little curvature, so light entering your eye is not focused correctly.

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Keratoconus is a vision disorder that occurs when the normally round cornea (the front part of the eye) becomes thin and irregular (cone) shaped. This abnormal shape prevents the light entering the eye from being focused correctly on the retina and causes distortion of vision.

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Macular degeneration is the leading cause of blindness in America. It results from changes to the macula, a portion of the retina that is responsible for clear, sharp vision and is located at the back of the eye.

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Nearsightedness, or myopia, as it is medically termed, is a vision condition in which near objects are seen clearly, but distant objects do not come into proper focus. Nearsightedness occurs if your eyeball is too long or the cornea has too much curvature, so the light entering your eye is not focused correctly.

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Nystagmus is a vision condition in which the eyes make repetitive, uncontrolled movements, often resulting in reduced vision. These involuntary eye movements can occur from side to side, up and down, or in a circular pattern. As a result, both eyes are unable to hold steady on objects being viewed. Nystagmus may be accompanied by unusual head positions and head nodding in an attempt to compensate for the condition.

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Ocular hypertension is an increase in the pressure in your eyes that is above the range considered normal with no detectable changes in vision or damage to the structure of your eyes. The term is used to distinguish people with elevated pressure from those with glaucoma, a serious eye disease that causes damage to the optic nerve and vision loss.

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Presbyopia is a vision condition in which the crystalline lens of your eye loses its flexibility, which makes it difficult for you to focus on close objects.

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Retinitis pigmentosa (RP) is a group of inherited diseases that damage the light-sensitive rods and cones located in the retina, the back part of our eyes. Rods, which provide side (peripheral) and night vision are affected more than the cones which provide color and clear central vision.

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Optometrists diagnose, refer, and comanage cancers that involve the eye area. The most common cancer involving the eye in young children is retinoblastoma. In the United States, this fast-growing cancer occurs in 1 in every 20,000 children, making it the tenth most common pediatric cancer.

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Spots (often called floaters) are small, semi-transparent or cloudy specks or particles within the vitreous, which is the clear, jelly-like fluid that fills the inside of your eyes. They appear as specks of various shapes and sizes, threadlike strands or cobwebs. Because they are within your eyes, they move as your eyes move and seem to dart away when you try to look at them directly.

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Strabismus occurs when one or both of your eyes turns in, out, up or down. Poor eye muscle control usually causes strabismus. This misalignment often first appears before age 21 months but may develop as late as age 6.

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20/20 vision is a term used to express normal visual acuity (the clarity or sharpness of vision) measured at a distance of 20 feet. If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. If you have 20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet.

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Eye & Vision Problems - American Optometric Association

You must wear glasses or contact lenses every time you drive if you need them to meet the standards of vision for driving.

You must tell DVLA if youve got any problem with your eyesight that affects both of your eyes, or the remaining eye if you only have one eye.

This doesnt include being short or long sighted or colour blind. You also dont need to say if youve had surgery to correct short sightedness and can meet the eyesight standards.

Check if you need to tell DVLA about your eyesight problem by searching the A to Z of medical conditions that could affect your driving.

You could be prosecuted if you drive without meeting the standards of vision for driving.

You must be able to read (with glasses or contact lenses, if necessary) a car number plate made after 1 September 2001 from 20 metres.

You must also meet the minimum eyesight standard for driving by having a visual acuity of at least decimal 0.5 (6/12) measured on the Snellen scale (with glasses or contact lenses, if necessary) using both eyes together or, if you have sight in one eye only, in that eye.

You must also have an adequate field of vision - your optician can tell you about this and do a test.

You must have a visual acuity at least 0.8 (6/7.5) measured on the Snellen scale in your best eye and at least 0.1 (6/60) on the Snellen scale in the other eye.

You can reach this standard using glasses with a corrective power not more than (+) 8 dioptres, or with contact lenses. Theres no specific limit for the corrective power of contact lenses.

You must have a horizontal visual field of at least 160 degrees, the extension should be at least 70 degrees left and right and 30 degrees up and down. No defects should be present within a radius of the central 30 degrees.

You must tell DVLA if youve got any problem with your eyesight that affects either eye.

You may still be able to renew your lorry or bus licence if you cant meet these standards but held your licence before 1 January 1997.

At the start of your practical driving test you have to correctly read a number plate on a parked vehicle.

If you cant, youll fail your driving test and the test wont continue. DVLA will be told and your licence will be revoked.

When you reapply for your driving licence, DVLA will ask you to have an eyesight test with DVSA. This will be at a driving test centre. If youre successful, youll still have to pass the DVSA standard eyesight test at your next practical driving test.

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Driving eyesight rules - GOV.UK

Many people don't understand the importance of having an eye exam. You find time to visit your family doctor for an annual physical. You manage to take your children to their pre-appointed six-month dental hygiene visits. But are you or your family overdue for a trip to the eye doctor's office? Vision care is often neglected. In reality, how much could we actually accomplish in a day without the precious gift of sight? The eyes function as a window to our bodies. Dilated pupils can reveal the presence of undiagnosed problems throughout the body. Here are four great reasons to schedule a comprehensive eye examination.

Your prescription needs to be checked on a regular basis to make sure your visual acuity is the best it can be. Annoying headaches or general fatigue are often caused by slight over or under corrections of your prescription. In addition, if you spend more than two hours on a computer each day, you may develop a condition known as computer vision syndrome, or CVS. Symptoms of CVS include headaches, focusing difficulties, burning eyes, tired eyes, eyestrain, aching eyes, dry eyes, double vision, blurred vision, light sensitivity, and neck and shoulder pain. CVS is treated with eyeglasses made for computer users.

Many serious eye diseases often have no symptoms. Glaucoma is an eye disease that causes vision loss and is commonly known as the "sneak thief of sight." Conditions such as macular degeneration or cataracts develop so gradually that you may not even realize your vision has decreased. Diabetic retinopathy is a condition that may develop in diabetic patients. Early detection of these and other eye diseases is important for maintaining healthy vision.

Uncorrected vision problems in children often cause learning and reading difficulties or contribute to other medical problems such as dyslexia and ADD. Uncorrected vision in children can often cause amblyopia (lazy eye) or strabismus (eye turn) which can cause permanent vision loss if not treated early in life.

The primary reason for visiting your eye doctor should always be eye health, but there is nothing wrong with having a little fun. Eye doctors who offer eyewear strive to stock the latest fashions and quality eyewear. Lens-making technology continues to improve, as well as scratch-resistant and anti-reflective coatings. If you haven't updated your glasses in a while, you may be pleasantly surprised at the many options available to you today. Sunglasses have also become a fashion accessory...check out your optical for the latest trends and styles.

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Eye Exam - Sight and Eye Exam - Vision and Eye Health ...

Have you been thinking of laser vision correction? Shed your doubts, concerns, specs and contact lenses, because blade free LASIK has arrived. With this technology, laser vision correction procedure has become 100 percent blade-free and completely safe.

In any LASIK procedure the first step is to create a corneal flap. In standard LASIK the surgeon uses a hand-held oscillating blade called microkeratome to cut the corneal flap. The flap is then folded and the Excimer laser treats the cornea to correct the refractive error.

In blade free LASIK, femtosecond laser has replaced the steel blade for creation of the corneal flap which improves visual outcome and post-operative comfort for the patient.

When you opt for advanced blade free LASIK procedure you get a completely integrated, personalized vision correction procedure based on cutting edge technology at every step. NASA recommends blade free LASIK to aspiring astronauts to get rid of their specs, as it can withstand high gravitational forces and has been found to be stable and secure even in extreme environmental conditions.

Advantages Precise corneal flap results in improved visual outcome Safer than standard LASIK Treats patients with high refractive errors and thin corneas too.

For people with nearsightedness (myopia), farsightedness (hyperopia) or astigmatism, LASIK surgery could be the key to a life free of bulky spectacles or contact lenses. But not everybody is a suitable candidate for this type of laser eye surgery. Here are the few main questions a LASIK surgeon is likely to ask you during a consultation.

Centre for Sight is equipped with trained and experienced eye specialists to help the patients in dealing of respective issues with specialization and care with advanced Blade-free LASIK surgery. This laser eye treatment creates flap in Blade-free LASIK which reduces risk of an irregular flap. You can trust our renowned eye specialists for Lasik eye surgery which is one of the Lasik Treatment in India.

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Laser Eye Treatment Center - Centre For Sight

Our visual systems perform all kinds of amazing jobs, from finding constellations in the night sky, to picking out just the right strawberry in the supermarket, to tracking a fly ball into a waiting glove. How do our eyes and brains recognize shape, movement, depth, and color? How do we so easily pick a friend's face out of a crowd, yet get fooled by optical illusions? In this first of three units on the Sense of Sight, we consider the anatomy and physiology of the eye, especially the retina, and the initial pathways visual information takes to the brain. Part 2 discusses how various aspects of a visual scene are processed at higher levels, and Part 3 delves into color vision.

1. Our eyes allow us to perceive electromagnetic radiation reflected from objects

Most animals and many plants are photosensitive; that is, they can detect different light intensities. Some organisms accomplish this with single cells or with simple eyes that do not form images but do allow the organism to react to light by moving toward or away from it. In order for an eye to transmit more information about the world, however, it must have a way of forming an image, a representation of the scene being viewed.

Higher invertebrates and virtually all vertebrates have complex, image-forming eyes, and we will "focus" on the refracting eye found in the octopus and in all vertebrates. Arthropods have compound eyes, which have greater depth of focus than refracting eyes, but which sacrifice resolving power or acuity. Our eyes, like those of many animals, detect a just narrow range of all the wavelengths of electromagnetic radiation, that between 380 and 760 nanometers. This range of light is called the visible spectrum. Figure 1 shows how the visible spectrum fits into the entire electromagnetic spectrum.

Figure 1. The electromagnetic spectrum and the visible spectrum.

2. The eyeball is an optical device for focusing light

The mammalian eyeball (Figure 2) is an organ that focuses a visual scene onto a sheet of specialized neural tissue, the retina, which lines the back of the eye. Light from a scene passes through the cornea, pupil, and lens on its way to the retina. The cornea and lens focus light from objects onto photoreceptors, which absorb and then convert it into electrical signals that carry information to the brain. Two pockets of transparent fluid nourish eye tissues and maintain constant eye shape: these are the aqueous and vitreous humors, through which the light also passes. The lens projects an inverted image onto the retina in the same way a camera lens projects an inverted image onto film; the brain adjusts this inversion so we see the world in its correct orientation. To control the images that fall upon our retinas, we can either turn our heads or turn our eyes independently of our heads by contracting the extraocular muscles, six bands of muscles that attach to the tough outside covering, or sclera, of the eyeball and are innervated by cranial nerves. See Table 1 for a brief list of eyeball components and their functions.

The cornea and lens bend or refract light rays as they enter the eye, in order to focus images on the retina. The eye can change the extent to which rays are bent and thus can focus images of objects that are various distances from the observer, by varying the curvature of the lens. The ciliary muscle accomplishes this by contracting to lessen tension on the lens and allowing it to round up so it can bend light rays more, or relaxing for the opposite effect. This ciliary muscle is smooth or non-voluntary muscle-you cannot "decide" to contract or relax it as you do the skeletal muscle in a finger or facial muscle.

Figure 2. The mammalian eyeball.

3. Refractive errors in the eye cause focusing problems

Refractive errors occur when the bending of light rays by the cornea and lens does not focus the image correctly onto the retina. An eyeball that is too long or too short for the optics of the cornea and lens or an irregularly shaped cornea can cause refractive errors, which include myopia (near-sightedness), hyperopia (far-sightedness), and astigmatism. Myopia results either when the eyeball is too long or when the cornea is curved too much, and the focused image falls in front of the retina. Hyperopia is the opposite, with the image falling behind the retina. Astigmatism results from a cornea that is not spherical. Fortunately, most refractive errors can be corrected with prescription lenses.

4. The retina originates from the brain and contains photoreceptors for detecting light

The eye is formed during embryonic development by a combination of head ectoderm and neural tube tissue, the latter forming the retina. Thus, the retina is not a peripheral sensory organ like skin touch receptors or taste buds on the tongue, but rather it is an outgrowth of central nervous tisse. Because of this origin, the retina has layers of neurons, internal circuits, and transmitters characteristic of the brain: it is a bit of the brain that has journeyed out, literally, to have a look at the environment.

The photoreceptors in the retina are of two types: rods and cones, so named because of their shapes. These cells are actually specialized neurons that detect light. Embedded in stacks of cell membranes in the distal portions of rods and cones are molecules that absorb certain wavelengths of light. These molecules are called photopigments and are composed of two parts: a large trans-membrane protein, an opsin, and a smaller chromophore, which is a metabolite of Vitamin A called 11-cis-retinal. The chromophore, which is embedded in the opsin, absorbs light; in so doing it undergoes a shape change. This shape change in turn activates the opsin, setting off a cascade of events that leads to a change in the electrical state of a rod or cone cell membrane. This change in the rod or cone cell membrane is then conducted via the rod or cone axon to other neurons in the retina, and from there to the brain.

5. Rods function in dim light

In dim light, we use our rods, which cannot work in bright light. Rods outnumber cones (120 million rods and about 6 million cones in each retina) and they amplify a light signal much more than cones. Scientists have demonstrated that absorption of even a single quantum (or photon) of light can trigger a chromophore shape change in one molecule of rhodopsin in a rod, leading to signal transmission. For transmission to occur, this initial tiny event must be amplified: the activated molecule of rhodopsin converts several thousand molecules of the next enzyme in the cascade to the active form, and this amplification continues until the electrical potential of the cell membrane changes and neurotransmitter release is affected. Cones, on the other hand, must each absorb hundreds of photons in order to send signals.

Another retinal mechanism that helps us to see in dim light or to see a tiny amount of light in the dark is the convergence of rod cell signals onto other retinal neurons. Many rods (up to 150) synapse onto the same target neurons, where the signals are pooled and reinforce one another, increasing the ability of the brain to detect a small amount of light. (A synapse is a contact between a neuron and another cell where an electrochemical signal [most commonly] is transmitted to the second cell.) This convergence amplifies weak signals, but spatial resolution is lost because rod responses are averaged. That is, we cannot see fine detail using rods.

In order for our eyes to make the transition to dim light, rods must adapt after being saturated with light in brighter conditions. Dark adaptation of rods takes seven to ten minutes: during this time rhodopsin molecules, in which the chromophore components have changed to the activated state, return to the non-activated state so that they are able once again to register changes in illumination. Other changes also occur in adaptation to dark or dim conditions, including enlarging or dilating of the pupil, which is controlled by the autonomic nervous system.

6. Cones mediate day vision

Our vision in bright or moderate light is completely mediated by cones, which provide color vision, black and white vision, and high acuity, the ability to discern fine detail. Like rods, cones contain an opsin and the chromophore 11-cis-retinal, but the opsins differ from rhodopsin so that each cone is responsive to one of three colors: red, green or blue. Cones are spread throughout the retina but are especially concentrated in a central area called the macula. At the center of the macula is the fovea, where only cones (no rods) are found, and these are densely packed. When we want to read or inspect fine detail, we move our heads and eyes until the image of interest falls onto the fovea. Because the fovea lacks rods, it is easier to see in dim light by looking to the side of an object instead of directly at it. You can test this by looking to the side of a faint star so that its image falls on rods, rather than on the fovea where it probably will not register. When you look directly at the faint star, it disappears.

In contrast to the wiring of rods, only a few cones converge onto other retinal neurons to average their signals, so cones provide better spatial resolution. In fact, each cone in the fovea synapses onto only one neuron in the next relay in the retina. This gives this area the ability to transmit fine detail, such as we use in reading.

Thus, cones mediate day vision and rods take over in dim light and at night. Both rods and cones can operate at the same time under some conditions: in dim or dark conditions, rods are most sensitive, but cones respond to stimuli that are sufficiently bright. This is why we can see the colors of neon lights on dark nights.

7. Visual information travels from retinal ganglion cells to the brain

After converting light into electrical signals in their cell membranes, rods and cones transmit this information to other neurons in internal circuits in the retina for processing. From these cells, messages go to the final retinal station, the ganglion cells, whose axons exit the eyeball at the optic disc and form the optic nerve, which contains about one million axons. Because all the nerve fibers converge at the optic disc, no rods or cones are in this area and it forms a "blind spot" on the retina: this may be easily demonstrated in a classroom activity.

Within the optic nerve, a defined group of axons from each eye crosses over to join the opposite optic nerve at the optic chiasma (see Figure 3), so each side of the brain receives visual information from both eyes. After the chiasma, retinal axons go to one of three areas: two of these are in the midbrain and one is in the thalamus. The information going to the midbrain does not reach conscious levels but rather produces pupillary reflexes (which are controlled by the autonomic nervous system) and eye movements. In the thalamus, ganglion cell axons transmit signals to neurons in the lateral geniculate nucleus (LGN) where information is processed and then carried by LGN axons to the primary visual cortex in the occipital lobe of the cerebrum. These cortical cells then send messages to other "higher" cortical areas. Figure 3 shows the anatomy of this system (the midbrain areas are not shown here).

Figure 3. The visual pathway

8. We have an area of central or focused vision and an area of peripheral vision within our fields of vision

The visual field is defined as the view seen by the two eyes while looking straight ahead (Figure 4). Without moving eyes or head, a person can see details (well enough to read) within a limited angle drawn from a point between the eyes on the forehead and two experimentally determined points to the left and right in front of the viewer, at proper focal distance. In addition to this area of clear or central vision, we can see objects and movements to the sides of our heads, although as the distance around to the sides increases, it becomes more difficult to identify objects. The area of central vision includes objects whose images fall onto the central area of the retina, the macula, and especially the fovea (defined above). Cones in all other areas of the retina are in the periphery, and while they convey visual information, they do not provide the resolving power of the densely packed fovea.

Figure 4. Complete visual field and central visual field, looking down onto the head. The complete visual field is the entire area in front of the eyes from the end of one lateral dashed line to the other (including the central visual field).

In addition to speaking of a central and a peripheral field of vision, we can divide these fields by a vertical line down the middle into right and left visual fields. Because of the way ganglion cell axons cross at the optic chiasma, information from the entire right visual field (to the right of a vertical line) goes to the left LGN, and from the left LGN, all axons go to the left occipital cortex (Figure 3). Similarly, all left visual field information goes to the right occipital cortex. Remember that although each visual cortex receives information only from the opposite visual field, this information is collected by defined parts of both eyes.

9. Projections from the retina to the brain generate retinotopic maps

As in the touch sensory system (and to some extent, other sensory systems), visual information is mapped in an orderly fashion onto neurons in the LGN of the thalamus. Further, this topographic mapping continues when LGN neurons carry signals to the visual cortex. As in the touch system, the mapping of the visual field is not isometric; that is, not every area of the visual field is represented in proportion to its size. Rather, the density of sensory neurons in a given area of the retina determines how many central neurons are devoted to that retinal area, as in the touch system where fingertips and lips have a much larger representation in the parietal cortex than do trunk and arms. In the LGN and primary visual cortex, about half of the neurons receive input from the fovea (the eye's "fingertips") and area just around it, where cones are densely packed and visual acuity is highest.

10. Defined groups of neurons in the primary visual cortex process different aspects of visual information

Several attributes of visual information go to the primary visual cortex: motion, form or shape, and color. These aspects of the visual scene travel to different modules or groups of cortical cells (some are given names such as "columns" or "blobs.") In order for us to perceive and interpret these kinds of visual information, other brain areas beyond the primary visual cortex must process the signals and put the visual scene back together.

11. Problems in different parts of the visual system can cause blindness

People who lose cone vision are legally blind, whereas loss of only rod function results in night blindness. Legal blindness is defined as 20/200 vision or worse; that is, a person is considered legally blind if he or she must be 20 feet away to see an object that a person with normal vision can see at 200 feet. Some forms of blindness result from damage to both rods and cones, while others originate with problems in different parts of the visual system. For example, people with damage to particular parts of the cerebral cortex lose specific aspects of vision, such as ability to see parts of the visual field, or to perceive motion, or to recognize faces. More information on these types of visual defects is given in Part 2 of this unit on the Sense of Sight.

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Neuroscience for Kids - The Eye and Its Connections