DISEASES OF THE EYE. 129 



eyes, as the organ is extremely intolerant of light; and the head should 

 be maintained in a somewhat elevated position, in order to facilitate the 

 return of blood from the inflamed vessels. 



When the attack is an isolated one, a diligent search should be made 

 for the causes which may have induced it; and any such causes, if dis- 

 covered, should, if possible, be removed or reversed. Thus, if the horse 

 is fat and in high condition, depletives may be beneficial; whilst, on the 

 other hand, if the animal is low, good feeding and tonics will be appro- 

 priate. As a tonic the following is recommended by some: 



Powdered Peruvian bark § ss. 



Sulphate of iron 3 i. 



to be given twice or three times a day. In most cases, however, specific 

 ophthalmia, in spite of all treatment, runs its course, sometimes unobtru- 

 sively and with scarcely noticeable force, and at other times with acute 

 symptoms. 



CATARACT. 



Cataracts are divided into true and spurious. The seat of true cata- 

 ract is in the crystalline lens, in its capsule, or in both, or even between 

 the lens and its capsule. Any opacity in the lens must seriously inter- 

 fere with the vision. So likewise, though in a lesser degree, any opacity 

 in the capsule or between the capsule and the lens will affect the power 

 of sight. There are three classes of true cataract distinguished as to 

 name by the position they occupy, namely, Lenticular, Capsular, and 

 Capsulo-lenticular or interstitial. 



The color of a cataract depends on various circumstances and esjoc- 

 cially on the length of time that has elapsed since its formation. In the 

 very early stage the lens may show only a slight nebulosity; later there 

 may be seen in it streaky lines radiating to a centre, and at last cataract 

 may be fully developed as a circumscribed white spot gradually increasing 

 in size. 



In rare cases a portion of the capsule of the lens may be partially 

 clouded, as a result of any injury or blow on the eye. Such cloudiness 

 is usually only temporary, though sometimes it may be persistent. 



Etiology. — As a general rule, after several attacks of ophthalmia the 

 9 



