128 



AMAUROSIS. 



The faculty of vision, for perfection and enjoyment, is dependent 

 upon integrity, as regards the component structures of the eye, and 

 upon suscej)til)ility, as regards the sensitive apparatus connected 

 with those structures. The coats and humours of the visual organ 

 may be all in a perfectly sound condition, and yet vision may be 

 either impaired or lost, because the nervous appurtenances of the 

 eye no longer possess the power of perceiving the rays of light, or, 

 at least, of having those impressions made upon them which are 

 necessary for the production of vision. This latter defect it is 

 which constitutes amaurosis. The sight, either much impaired or 

 quite gone, is said to be a^uvpoQy obscure. The same disorder is 

 also called gutta serena, and by common farriers, glass eyes, from 

 the more than ordinary brilliancy the eyes possess, owing to the 

 unnaturally dilated state of the pupils. 



An obvious Difference between amaurosis as it ordinarily 

 exists and other diseases of the eye therefore is, that in the one 

 case there is nothing to obstruct the transit of the rays of light to 

 the bottom of the eye ; in the other, from obscurities of parts, from 

 contraction or obliteration of the pupil, the rays are divided or in- 

 tercepted in their course ; and yet in both cases the effects, as 

 regards vision, may be similar. 



Amaurosis may proceed from some disease of the retina 

 itself, in which form it is said to be idiopathic ; or from some 

 anormal condition of the optic nerve or the brain, or, according 

 to Magendie, even of the ophthalmic division of the fifth pair of 

 nerves, in either of which cases the disorder can be regarded but 

 as symptomatic ; or, lastly, it may prove the last link of a series 

 of morbid phenomena originating in some remote part of the body, 

 operating sympathetically on the nervous system, and through it 

 extending to the eye : a case denominated sympathetic amaurosis. 

 Of these species or forms of the disease the symptomatic is the 

 one of most common occurrence in horses. 



The Nature of Amaurosis will vary with the nature and 

 situation of the cause from which it originates. I have, in a former 

 place, stated that now and then it is present in periodic ophthalmia. 



