CHAPTER V. 

 DISEASES OF THE IRIS AND CILIARY BODY. 



General.— In practice it is very difficult to separate the 

 diseases of the iris and ciliary body of which the iris is 

 practically an extension. The structure of the iris is much 

 the same in all animals. The arrangement of its muscular 

 fibers in different animals accounts for the variation in the 

 shape of the pupil. In the cat the pupil is an elongated 

 slit; in dogs it is spherical or oval. 



The color of the iris is due to the quantity of pigme nt 

 present in the posterior layers and in the membrane proper. 

 Frequently the pigment is entirely absent producing the 

 albino or pink eye. This is common in rabbits and is 

 occasionally observed in other animals. The other colors, 

 such as blue, black or gray eyes, are determined by the 

 amount and distribution of the pigment. A more com- 

 plete examination of the iris can be made if a few drops of 

 eserin are instilled into the eye to contract the pupil. The 

 examination should be made for congenital defects, inflam- 

 mations, tumors, etc. 



CONGENITAL DEFECTS OF THE IRIS. 



A number of defects in the formation and development 

 of the iris has been observed: (a) Occlusion of the pupil, 

 occurring in the dog, cat and rabbit, causing congenital 

 blindness, (b) Ectopia pupillae, a displacement of the 

 pupil often found accompanying luxation of the lens, (c) 

 Coloboma, a portion of the iris failing causing a large, 

 irregular-shaped opening, (d) Aniridia, absence of the iris, 

 very unusual in animals. Treatment for these conditions 

 is unsatisfactory. The size and form of the pupil are 

 influenced by light, disease and medication. 



