130 VETERINARY MEDICINE AND SURGERY. 



pupil dilates and clears, and cataract forms. But in special cases the 

 pupil may remain constantly contracted, because adhesion has taken 

 place between the capsule of the lens and the iris; or, on the other hand, 

 the pupil may remain abnormally open, if there is paralysis of the optic 

 nerve or a tendency to amaurosis. In such a case the eye is more toler- 

 ant of light, because less susceptible of its effect. 



Lenticular cataract, or in other words partial or complete opacity of 

 the lens, is the result of the deposits left by the repeated attacks of in- 

 flammation. The effusion is at first interspersed through the substance 

 of the lens, but gradually, as the more watery parts of the effusion are 

 taken up, the deposit concentrates to one spot and forms the opaque 

 speck known as cataract. Cataracts are generally of very gradual forma- 

 tion. The first attack of inflammation, though it probably leaves some, 

 yet generally gives rise to no perceptible deposit or opacity; but after 

 several attacks the deposit or speck becomes apparent. 



In old horses similar changes sometimes go on insensibly, ending in 

 cataract without any perceptible periodical attacks of inflammation. 



Capsular cataract proceeds from the same causes and is formed in 

 much the same way as lenticular; but for some reason not very easy to 

 explain, the deposit fixes itself on the inner surface of the capsule in- 

 stead of in the lens. If the lens be examined by a good reflected light, 

 it will be found to be clear behind its capsule. 



In some cases capsular cataracts form from other causes than at- 

 tacks of specific opthalmia. In such, it is probable that the deposit on 

 the capsule may be absorbed, and the eye restored to its pristine state. 



The third variety of true cataract, known as Capsulo-lenticular or In- 

 terstitial cataract, is found in the form of an opaque fluid between the 

 lens and its capsule. 



By taking a side view of the eye, these cataracts are easily distin- 

 guished from lenticular, because the transparency of the lens can then 

 be seen behind the opaque deposit. 



Symptoms. — The state of the pupil is best seen in a diminished light. 

 The existence or otherwise of cataract, the proper motion of the iris , 

 and the state of the structures of the eye generally are then, as a rule, 

 very easily observed. But in some cases it is advisable to take the horse 

 into a darkened stable and to examine his eye by the light of a candle, 

 when the pupil will be found to be fully expanded. 



In health, when a candle is moved before the fully expanded pupil. 



