DISEASES OF THE EYE. 



By James Law, F, R. C. V. S., 

 Professor of Veterinary Science, etc., Cornell University. 



[Revised lu lOO:^ by the author.] 



We can scarce!}' overestimate the value of sound eyes in the horse, 

 and hence all diseases and injuries 'which seriously interfere with 

 vision are matters of extreme gravity and apprehension, for should 

 they prove permanent they invariably depreciate the selling price to 

 a considerable extent. A blind horse is always dangerous in the sad- 

 dle or in single harness, and he is scarcely less so when, with partially 

 impaired vision, he sees things imperfectly, in a distorted form or in 

 a wrong place, and when he shies or avoids objects which are com- 

 monplace or familiar. \Mien we add to this that certain diseases of 

 the eyes, like recurring inflammation (moon blindness), are habitu- 

 ally transmitted from parent to offspring, we can realize still more 

 fully 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 

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

 delicate friable memlirane, consisting mainly of blood vessels and 

 pigment cells (the choroid), and that in its turn is lined by the ex- 

 tremely delicate 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 thus 

 forms a segment of a much smaller sphere than is inclosed by the 

 sclerotic. Its walls, too, have in health a perfect translucency from 

 which it has derived the name of transparent cornea. This trans- 

 parent coat is composed, in the main, of fibers with lymph interspaces, 

 and it is to the condition of these and their condensation and com- 

 pression that the translucency is largely due. This may be shown 

 by compressing with the fingers the eye of an ox which has just been 

 killed, when the clear transparent cornea will suddenly become 



251 



