DISEASES OF THE EYE. 413 



not indeed for the cure, but for the relief of this disease. The horse, as 

 previously stated, possesses a very peculiar power of withdrawing at will 

 the eye into its socket, which would much increase the difficulty of per- 

 forming any operation ; but even if this difficulty be got over, the opera- 

 tions common in human surgery, such as couching the crystalline lens, 

 would not be of any use, as it is obviously impossible to supply the horse 

 with glasses. 



855. Spurious Cataracts. 



Spurious cataracts are opaque specks on the cornea, or flocculi of 

 lymph in the anterior chamber of the aqueous humour, generally adherent 

 to the anterior surface of the capsule of the lens or to the posterior sur- 

 face of the cornea. They are generally the result of an effusion of lymph 

 arising from the inflammation of common ophthalmia, into the aqueous 

 humour. They are also occasionally found as a result of the specific 

 disease. 



The amount of detriment which they occasion to vision depends on 

 their size and position. If on the cornea, they will not interfere much, 

 but on the capsule they become a more serious evil. 



Spurious cataracts are frequently absorbed after a time. Sometimes 

 they appear quite suddenly and without any apparent cause, and disap- 

 pear as suddenly. 



856. Amaurosis. 



Amaurosis, partial or complete, results from paralysis of a part or of 

 the whole of the optic nerve. According to the degree of the affection, 

 the blindness may be total or partial. The eye is generally in all other 

 respects perfect. On account of the insensibility of the retina to the 

 effects of light, the pupillary opening remains unnaturally large, the 

 pupil possesses more than ordinary brilliancy, and the eye has a ghastly 

 stare. This appearance of the pupil at once points out the cause of 

 blindness. Again, in his action the animal has all the appearance of a 

 blind horse. In partial amaurosis the movement of the iris may not be 

 wholly lost. It may be only sluggish. 



857. Causes. 



Disease of the optic nerve may proceed from various causes either 

 peculiar to that one nerve, such as excess of glare or heat, or from pres- 

 sure on it, such as that induced by the formation of a tumour, by extrava- 

 sation of blood, or any morbid effusion ; or it may proceed from some 

 abnormal condition of the brain generally, induced by causes such as 

 those last named. Disease of the optic nerve may also proceed from 

 some abnormal condition of the body, such as an overloaded stomach, 

 which affects the nervous system generally, and with it the nerve of the 

 eye. 



Amaurosis is also occasionally, though but rarely, the result of the 

 violent inflammatory action of specific ophthalmia; and it occasionally 

 arises from extreme debility of the whole system or from excessive loss 



