The Anatomy of the Equine Eye­ball

Practical Horseman - - Inside Your Ride -

Aqueous hu­mor – This clear, wa­tery fluid is held in cham­bers be­hind the cornea. It de­liv­ers oxy­gen and nutri­ents while re­mov­ing waste. Choroid – The pig­mented mem­brane lo­cated be­tween the retina and sclera. Its net­work of blood ves­sels sup­plies oxy­gen and nutri­ents to the retina. Cil­iary body – Lo­cated be­hind the iris and at­tached to the lens, it helps change the shape of the lens. Con­junc­tiva – A thin, clear mem­brane that cov­ers the sclera and lines the in­side of the eye­lid. It cre­ates a bar­rier that helps pre­vent ob­jects from get­ting into the back of the eye. Cornea – The trans­par­ent layer that forms a dome-like cover over the eye­ball. It’s crit­i­cal to the eye’s abil­ity to fo­cus. Iris – The col­ored part of the eye. It works to make the pupil larger or smaller, reg­u­lat­ing how much light en­ters. Lens – Lo­cated be­hind the iris and pupil, this disc-like tis­sue is flex­i­ble and elas­tic, al­low­ing it to change shape to as­sist with fo­cus­ing. Op­tic nerve – A cable-like nerve that sends light sig­nals from the retina to the brain, which con­verts those sig­nals to an im­age. Pupil – The hole in the cen­ter of the iris that lets light pass through. It can en­large (di­late) to let in more light and shrink to let in less light. Retina – An ex­tremely thin layer lin­ing the back of the eye. It absorbs light and trans­mits it through the op­tic nerve to the brain. Sclera – The outer, white layer of the eye­ball, made of a dense, fi­brous mem­brane. It helps pro­tect the eye and con­trol eye move­ment. Third eye­lid – Also known as the nic­ti­tat­ing mem­brane, this is es­sen­tially a clear eye­lid that will au­to­mat­i­cally move across the eye­ball as an­other layer of pro­tec­tion that still al­lows the horse to see. Uvea – The layer un­der the sclera, made up of the iris, the choroid and the cil­iary body (not pic­tured above) Vitre­ous hu­mor – This clear, gel-like fluid fills a space at the back part of the eye. It helps hold the retina in place and acts as a shock ab­sorber for the in­side of the eye.

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