CHAPTER VI. 



DISEASES OF THE LENS. 



Examination. —The lens is best examined after dilating 

 the pupil with atropin. The patient should be placed in 

 a good light or light may be reflected with an ophthalmo- 

 scope against the lens. Normally the lens is transparent. 

 It should be examined for turbidity, position and form. 

 In old dogs the lens is usually less transparent than in 

 younger animals. 



CATARACT. 



Definition.— An opacity of the lens, its capsule or both. 

 Cataract is common in the dog and cat, especially in old 

 animals. The following kinds occur: (a) Symptomatic, 

 (b) traumatic, (c) senile, (d) diabetic, (e) congenital. 



Symptomatic Cataract.— This, form results from an inflam- 

 mation of some of the adjacent structures which interferes 

 with the nutrition of the lens. In the dog and cat it often 

 develops from distemper. 



Traumatic Cataract.— Traumatic cataract is caused by 

 injury to the lens by sharp objects which penetrate the 

 cornea. Or it may be due to indirect injury, the animal 

 receiving a blow which jars the lens from its fastenings. It 

 may, therefore, result from fracture of the orbit or some of 

 the other bones of the head. 



Senile Cataract.— Common in old dogs. It is due to an 

 atrophy of the lens and is usually bilateral. In the early 

 stages senile cataract usually appears as radiating, gray 

 lines which extend from the periphery to the center of the 

 lens. In other cases it may occur as an opaque spot or 

 spots in the lens. The opacity spreads until eventually the 

 entire lens is involved. 



