Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems. Since ophthalmologists perform operations on eyes, they are considered to be both surgical and medical specialists. Eye examination, with aid of slit lamp The word ophthalmology comes from the Greek roots ophthalmos meaning eye and logos meaning word, thought, or discourse; 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. Sushruta 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.[1][2] His description of cataract surgery was more akin to extracapsular lens extraction than to couching.[3] He has been described as the first cataract surgeon.[4][5] [edit]Pre-Hippocrates The pre-Hippocratics largely based their anatomical conceptions of the eye on speculation, rather than empiricism. 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 via 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. [edit]Rufus Rufus of Ephesus recognised a more modern eye, with conjunctiva, extending a

a fourth epithelial layer over the eye. 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. [edit]Middle Eastern ophthalmology Main article: Ophthalmology in medieval Islam Medieval Islamic physicians are considered founders of ophthalmology as an independent discipline.[6][verification needed] One of the pioneers of ophthalmology was the Persian physician Rhazes. Ibn al-Haytham (Alhazen) wrote extensively on optics and the anatomy of the eye in his Book of Optics (1021). He was the first to hint at the retina being involved in the process of image formation.[7][page needed] Ibn al-Nafis, in The Polished Book on Experimental Ophthalmology, discovered that the muscle behind the eyeball does not support the ophthalmic nerve, and that the optic nerves transect but do not get in touch with each other. He also discovered new treatments for glaucoma and the weakness of vision in one eye when the other eye is affected by disease.[8] Salahud-din bin Youssef al-Kalal bi Hama (i.e. the eye doctor of Hama) was a Syrian oculist who flourished in Hama in 1296. He wrote an elaborate treatise of ophthalmology entitled Nur al-Uyun wa Jami al-Funun (light of the eyes and collection of rules).