DISEASES OF THE IRIS AND CILIARY BODY iii 



Congenital defects of the pupil are often noticed, and 

 one of the most common is a persistent pupillary mem- 

 brane. It is common in man, and has been seen in the 

 horse, ox, dog, and rabbit. Youatt mentions a case 

 of congenital blindness from this cause in a female 

 pointer eight weeks old (Steel's ''Diseases of the Dog"). 

 ''Meyer notes the case of a congenital double pupil 

 in a horse; a bridge extending across the space from the 

 upper to the lower border, and cutting off the outer 

 third of the opening" (Law's "Veterinary Medicine"). 

 Ectopia pupillcB, or displacement of the pupil, is not 

 uncommon, and frequently accompanies luxation of the 

 lens. Colohoma of the iris is a condition in which a por- 

 tion of the iris is absent from the border of the pupil 

 to the periphery, causing a large, irregular opening. 

 Aniridia is a condition in which the iris is absent. 

 These congenital defects should not be confounded with 

 pathologic conditions following iritis, injuries, etc. 



The size and shape of the piipil vary in different 

 animals, and are influenced by light, darkness, ac- 

 commodation, medication, and disease. 



Mydriasis, or dilatation of the pupil, is due to paralysis 

 of the third nerve, irritation of the ciHospinal center, 

 constitutional diseases, diseases of the central nervous 

 system, contusions, intra-ocular pressure, and certain 

 drugs known as mydriatics. 



Myosis, or contraction of the pupil, is caused by 

 paralysis of the cervical sympathetic, tabes dorsalis, 



