The Head and Neck 51 



CATARACT. 



This term is used to denote any opacity of the crystalline lens 

 or its capsule. It is a common trouble. It is sometimes congenital 

 in origin, and sometimes traumatic from contusions and wounds, 

 but most frequently occurs incident to senility. The nature of 

 its development is not properly understood but it is believed to be 

 due to some condition interfering with the nutrition of the lens, 

 and heredity is known to play a part. Cataracts are also seen in 

 cases of diabetes mellitus. A cataract may be partial or complete, 

 unilateral or bilateral, and according to the stage of its development 

 may be soft or hard and consist of isolated spots, striae, or peri- 

 pheral, central, or total opacities, of white, bluish, or amber color. 

 Congenital cataracts show little tendency to further development, 

 but those arising in young animals increase in density at a rapid 

 rate. Senile cataracts on the other hand run a protracted course. 



A cataract sometimes undergoes displacement or complete lux- 

 ation. 



Symptoms and Diagnosis. The first symptom is impairment of 

 visual acuity and this becomes more and more marked as the con- 

 dition increases in intensity until total blindness is established. The 

 eye being examined, the telltale opacities are discovered, though 

 these, when slight, may be imperceptible without an ophthalmo- 

 scopic examination. Pupillary action may remain normal. 



Treatment. As has been observed by Cadiot and Breton, cat- 

 aract never retrocedes in the dog and its treatment is exclusively 

 surgical and an operation beneficial. Theoretically, removal of the 

 lens could leave the subject capable of but vague sensation of near- 

 by objects. But, in reality, as has been observed by Cocteau and 

 Leroy, Contejean, Randolph, Moeller, and others, recovery of 

 almost perfect vision is the rule. This takes place progressively in 

 one to three months. At first the animal runs into obstacles and 

 scents its food before partaking. Distant objects and particularly 

 persons calling, are seen perfectly, and the animal runs at once ; but 

 in approaching, it can no longer see and hunts around guided by the 

 voice. As the improvement takes place, accommodation, which is 

 always within narrow limits under normal conditions, is re- 

 established. Contejean holds that the lens is not regenerated and 

 cites the absence of Purkinje's images as evidence. But this he 

 regards as unnecessary suggesting that certain muscular fibers can 



