CHAPTER XII 



DISEASES OF THE LENS 



Cataract. — A cataract is an opacity of the crystalline 

 lens, its capsule, or both. Animals are as subject to 

 cataract as man. The horse, dog, and cat are frequently 

 seen with cataractous lenses. 



Normally, the lens is transparent, but as one advances 

 in life it becomes less transparent and assumes a hazy 

 appearance when viewed obliquely. This is due to an 

 increase in its density. Under this condition the vision is 

 probably as good as in early life, when the lens is much 

 softer, though often in man the density becomes so great 

 that near-sightedness is developed by virtue of changes 

 in its refraction. In such instances elderly people read 

 print without the aid of glasses, and they think, as is 

 often remarked, they have their ''second sight." Such 

 cases, however, are apt to be followed by cataractous 

 changes. 



Classification. — Cataracts are classified, according to 

 age, density, course, etc., as congenital, senile, soft, 

 hard, incipient, mature, primary, secondary, capsular, 

 lenticular, stationary, progressive, traumatic, etc. 



When an animal is born with cataractous lenses it is 



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