lo8 OPHTHALMOLOGY FOR VETERINARIANS 



it takes a long time to accomplish any degree of clear- 

 ness. When the opacity is centrally located, and it 

 cannot be made clear by medication, an iridectomy may 

 be done for optical effect. 



Interstitial Keratitis. — This is also known as paren- 

 chymatous keratitis, keratitis profunda, and keratitis 

 diffusa. 



It is essentially a disease of the young, and the usual 

 cause in man is hereditary syphihs, though it frequently 

 occurs in dogs as a result of distemper. It may begin at 

 the center or margin of the cornea, as a grayish macula 

 located in the stroma. This gradually extends until 

 the whole cornea becomes invaded, and the tissues 

 become opaque and assume a ground-glass appearance. 

 On close inspection vessels may be seen ramifying 

 through the deep layers, while some have tuft-like 

 branches near the margin. The disease is very pro- 

 tracted in its course, and one or more months may 

 elapse before it has reached its height, when the severity 

 of the symptoms will gradually subside, and it may 

 then require months before the cornea will resume its 

 normal transparency; and there is a probability that it 

 will never become transparent again. In some cases 

 the disease is more localized and confined to small 

 areas. As a rule the vascular condition exists in pro- 

 portion to the extent and degree of infiltration. There 

 are non- vascular forms, however, in which very few 

 vessels can be seen. Being confined to the stroma. 



