DISEASES OF THE EYE. 



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

 Formerly Professor of Teterinarii Science, etc., Cornell University. 



We can scarcely 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 j)ermanent 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 partiall}'^ 

 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. AMien 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. 



STRUCTURE OF THE EYE. 



(PI. XXII.) 

 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 jSbrous 

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

 delicate, friable membrane, consisting mainlj'^ of blood vessels and 

 pigment cells (the choroid), which 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 translucencj^, from 

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

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

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