DISEASES OF THE OPTIC NERVE 135 



It is manifest by a gradual or rapid reduction in sight. 

 The central field is the one involved, and from this fact 

 it is possible that the poison may attack the nerve ele- 

 ments of the macula first and then recede to the optic 

 nerves. Colors are not easily distinguished, especially 

 red and green. 



The treatment in such cases is to remove the cause, 

 keep the bowels open, and tone up the nerve-fibers by the 

 use of strychnin. 



Atrophy of the optic nerve may be simple or inflam- 

 matory. In the former the nerve head becomes gradually 

 white, without symptoms of inflammation accompanying 

 it. The sight is gradually reduced until there is com- 

 plete blindness. The principal causes are affections of 

 the brain and tabes dorsahs (sclerosis of the posterior 

 columns of the spinal cord). The author once saw a 

 case of this kind in a cat in which both optic nerves 

 were entirely atrophied, with sight and locomotion 

 abolished. 



Inflammatory atrophy is the result of optic neuritis, 

 with symptoms like those described under Papillitis. 

 After the swelling of the nerve head subsides the out- 

 line becomes more distinct and smaller in size, and the 

 large and tortuous vessels become contracted. The 

 papilla has a white appearance, sharply defined. The 

 prognosis is always unfavorable. 



The treatment should be aimed at the cause, together 

 with tonics and alteratives for the nerve lesion. . 



