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Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye.[1] An ophthalmologist is a specialist in medical and surgical eye problems. Since ophthalmologists perform operations on eyes, they are both surgical and medical specialists. A multitude of diseases and conditions can be diagnosed from the eye.[2]

The word ophthalmology comes from the Greek roots , ophthalmos, i.e., "eye" and -o, -logia, i.e., "study of, discourse";[3][4] ophthalmology literally means "the science of eyes". As a discipline, it applies to animal eyes also, since the differences from human practice are surprisingly minor and are related mainly to differences in anatomy or prevalence, not differences in disease processes.[citation needed]

The Indian surgeon Sushruta wrote Sushruta Samhita in Sanskrit in about 800 BC which describes 76 ocular diseases (of these 51 surgical) as well as several ophthalmological surgical instruments and techniques.[5][6] His description of cataract surgery was more akin to extracapsular lens extraction than to couching.[7] He has been described as the first cataract surgeon.[8][9]

The pre-Hippocratics largely based their anatomical conceptions of the eye on speculation, rather than empiricism.[10] They recognized the sclera and transparent cornea running flushly as the outer coating of the eye, with an inner layer with pupil, and a fluid at the centre. It was believed, by Alcamaeon and others, that this fluid was the medium of vision and flowed from the eye to the brain by a tube. Aristotle advanced such ideas with empiricism. He dissected the eyes of animals, and discovering three layers (not two), found that the fluid was of a constant consistency with the lens forming (or congealing) after death, and the surrounding layers were seen to be juxtaposed. He and his contemporaries further put forth the existence of three tubes leading from the eye, not one. One tube from each eye met within the skull.

Rufus of Ephesus recognised a more modern eye, with conjunctiva, extending as a fourth epithelial layer over the eye.[11] Rufus was the first to recognise a two-chambered eye, with one chamber from cornea to lens (filled with water), the other from lens to retina (filled with an egg white-like substance). The Greek physician Galen remedied some mistakes including the curvature of the cornea and lens, the nature of the optic nerve, and the existence of a posterior chamber.

Though this model was a roughly correct modern model of the eye, it contained errors. Still, it was not advanced upon again until after Vesalius. A ciliary body was then discovered and the sclera, retina, choroid, and cornea were seen to meet at the same point. The two chambers were seen to hold the same fluid, as well as the lens being attached to the choroid. Galen continued the notion of a central canal, but he dissected the optic nerve and saw that it was solid. He mistakenly counted seven optical muscles, one too many. He also knew of the tear ducts.

Medieval Islamic Arabic and Persian scientists (unlike their classical predecessors) considered it normal to combine theory and practice, including the crafting of precise instruments, and therefore found it natural to combine the study of the eye with the practical application of that knowledge.[12]

Ibn al-Haytham (Alhazen), an Arab scientist with Islamic beliefs, wrote extensively on optics and the anatomy of the eye in his Book of Optics (1021).

Ibn al-Nafis, an Arabic native of Damascus, wrote a large textbook, The Polished Book on Experimental Ophthalmology, divided into two parts, On the Theory of Ophthalmology and Simple and Compounded Ophthalmic Drugs.[13]

In the 17th and 18th centuries, hand lenses were used by Malpighi, and microscopes by van Leeuwenhoek, preparations for fixing the eye for study by Ruysch, and later the freezing of the eye by Petit. This allowed for detailed study of the eye and an advanced model. Some mistakes persisted, such as: why the pupil changed size (seen to be vessels of the iris filling with blood), the existence of the posterior chamber, and of course the nature of the retina. In 1722, van Leeuwenhoek noted the existence of rods and cones,[citation needed] though they were not properly discovered until Gottfried Reinhold Treviranus in 1834 by use of a microscope.

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