DISEASES OF THE CORNEA 91 



of a cicatrix or scar, which is opaque. If the perforation 

 is not over the pupillary area it does not materially in- 

 terfere with vision except by traction upon the iris 

 over the point of prolapse, which causes a dislocated 

 pupil to the point of prolapse or adhesion. If per- 

 foration occurs over the pupillary area a permanent 

 fistula may be the result, or the anterior capsule of the 

 lens may be drawn into the wound and an adhesion 

 takes place. An opacity then occurs at this point which 

 interferes with vision very greatly, as it is directly in the 

 central field. 



Causes. — Traumatism is the most common cause, 

 such as the presence of a foreign body or the careless 

 removal of one, followed by infection; scratching the 

 cornea by a twig or whip; a misdirected eyelash; a burn, 

 or an injury which breaks the epithelium and carries 

 infection with it, or later becomes infected. Infection 

 is the ultimate cause of all corneal ulcers. When free 

 from infection much mechanical injury of the cornea 

 may be done without purulent inflammation following. 

 Exposure keratitis, followed by ulceration, may be 

 primarily caused by lagophthalmus, exophthalmus, and 

 paralysis of the fifth nerve. Purulent diseases of the 

 conjunctiva and lacrimal apparatus, cow-pox, in- 

 fluenza, and other infectious diseases are common 

 causes. The streptococcus, staphylococcus, pneumo- 

 coccus, and other pyogenic bacteria are the infecting 

 agents. 



