DISEASES OF THE BYE. 



By James Law, F. R. C. A\ 8., 



Prof elisor of Veterinary Science, etc., Cornell UniverffUy. 



[Revised in 1903 bj- tlie author.] 



We can scarcely overestimate the value of sound eyes in the horse, 

 and hence all diseases and injuries which serioush" interfere with vision 

 are matters of extreme gravity and apprehension, for should they prove 

 peraianent the}" invariably depreciate the selling price to a considerable 

 extent. A blind horse is alwa3'S dangerous in the saddle or in single 

 harness, and he is scarcely less so when, with partially impaired vision, 

 he sees things imperfecth', in a distorted form or in a wrong place, and 

 Avhen he shies or avoids objects which are commonplace or familiar. 

 When we add to this that certain diseases of the eyes, like recurring 

 inflammation (moon blindness), are habitually transmitted from parent 

 to ofl'spring, we can realize still more full}" the importance of these 

 maladies. Again, as a mere matter of beauty, a sound, full, clear, 

 intelligent eye is something which must always add a high value to 

 our equine friends and servants. 



THE EYEBALL. * 



A full description of the structure of the eye is incompatible with 

 our prescribed limits, and yet a short description is absolutely essen- 

 tial to the clear understanding of what is to follow. 



The horse's eye is a spheroidal body, flattened behind, and with its 

 posterior four-fifths inclosed by an opaque, white, strong fibrous mem- 

 brane (the sclerotic), on the inner side of which is laid a more delicate 

 friable membrane, consisting mainly of blood vessels and pigment 

 cells (the choroid), and that in its turn is lined by the extremely deli- 

 cate and sensitive expansion of the nerve of sight (the retina). The 

 anterior fifth of the globe of the eye bulges forward from what would 

 have been the direct line of the sclerotic, and thiLS forms a segment of 

 a much smaller sphere than is inclosed by the sclerotic. Its walls, 

 too, have in health a perfect trauslucency from which it has derived 

 the name of transjmrent cornea. This transparent coat is composed, 

 in the main, of fibers with lymph interspaces, and it is to the condi- 

 tion of these and their condensation and compression that the trans- 

 lucency is largely due. This may be shown by compressing with the 



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