Paralysis of the Nerves of the Eye. 717 



often produces the opposite effect. Infraiiuclear paralysis is 

 often associated with the loss of conductivity in the motor 

 fibers in a mixed nerve. Sensation persists in the paralyzed 

 area, and it may be either exaggerated, but it is diminished or 

 completely lost if the conductivity of the sensory nerves has 

 been destroyed by some very severe inflammation. 



1. Paralysis of the Nerves of the Eye. 



Etiology. Paralysis of the III, IV and VI pairs of cranial 

 nerves is generally due to some intracranial disease (menin- 

 gitis, concussion of the brain, encephalitis, tumors), and is of 

 fairly frequent occurrence under such circumstances. (In a 

 case recorded by Zschokke, the abductor nerve was subjected 

 to pressure by an intracranial angioma.) There are no cases 

 on record of extracranial disease of these nerves, but injuries 

 might occur through fractures of Ijone in their immediate 

 neighborhood, or through the presence of exostoses or tumors in 

 the depth of the orbit. 



In cases of torsion of the eyeball recorded in horses by Bal- 

 langee and Bayer, Clerchet, Fayet & Nicolas, the cause was not 

 discovered. 



Symptoms. Paralysis of the oculo-motor nerve is observed 

 most frequently, the condition l)eing more rare in the abduc- 

 tor and trochlear nerves. In cases of paralysis of the oculo- 

 motor the upper eyelid is dropped (ptosis), the animal is nn- 

 able to open the eye, but is able to lift the upper lid to a certain 

 extent by powerful contraction of the corrugator supercilii, 

 which is supplied by the facial nerve. The bulb of the eye 

 is directed outwards and its outer half somewhat upwards 

 (strabismus divergens). The pupil is dilated and does not 

 react to light. On pressure the eye is not retracted into the 

 orbit and the membrana nictitans is consequently not seen. 



Paralysis of the external rectus muscle, wliich is supplied 

 by the abducens nerve, causes the eyeball to turn inwards 

 (strabismus convergens), while paralysis of the trochlear nerve, 

 which supplies the superior oblique muscle, causes the eye to re- 

 volve with its onter part downwards. 



Dexler has repeatedly observed exophtliahinis in cattle, also convergent squint- 

 ing, and functional disturbances of the muscles of the eyes associated with secondary 

 catarrh of the conjunctiva. The cause was in all probability an increase in the 

 intraorbital fat. 



Prognosis. Improvement is scarcely to be hoped for, but 

 it depends upon the nature of the primary disease. Exceptions 

 to this rule are many cases of concussion of the brain or rota- 

 tion of the eyeball' without other disturbances (Ballangee). 



