PERIODIC OPHTHALMIA. 343 



but, if softer, most emphatically contraindicated, for surgical inter- 

 ference means an early and incurable blindness. . . . It is 

 well to remember that, when one eye is affected with this disease, 

 the other will, as a rule, become affected sooner or later. This 

 should be especially remembered, for when you have one eye 

 cleared up and apparently sound, a month or two later you are 

 called to test the other eye, affected more or less severely from 

 sympathy, direct nerve influence, or infection." Dr. Harrison 

 allows an escape of aqueous hmiiour sufficient to give the cornea 

 a flattened appearance. " 'Care must be exercised that the flow 

 of the fluid is very gradual, so that the lens may not be torn 

 from its attachments, or the iris involved." In operating on the 

 apparently sound eye, a s.maller quantity of aqueous humour is 

 allowed to escape. Out of 100 cases in Dr. Harrison's practice, 

 80 recovered, 10 showed an improvement, and 10 did badly. 

 Veterinary Surgeon Desmond has also had excellent results from 

 this operation in periodic ophthalmia. 



Cataract 



is an opaque condition of the crystalline lens, or of its capsule, or 

 of both structures at the same time, by reason of which the light 

 that enters the pupil is obstructed on its way to the retina ; blind- 

 ness, total or partial, being the natural result. A cataract may 

 consist of only a small white or bluish-white spot which slightly 

 obscures the vision, and it may then be the cause of shying in the 

 animal ; or it may completely cover the affected structures. In 

 the former case, if the horse be taken into a dark room and the 

 eye be examined by the light of a candle, the speck may be seen 

 through the pupil, which will, more or less perfectly, contract or 

 dilate on the approach or removal of the taper ; but in the latter, 

 the cataract will appear like a white curtain drawn across the open- 

 ing of the pupil, which will probably then be quite insensible to 

 the action of light. A careful comparison of the behaviour of both 

 eyes under the influence of the light of a candle in a room in which 

 there is no other source of light, will aid the correctness of the 

 examination. White specks on the cornea should not be con- 

 founded with cataract. 



An examination of the eyes in daylight is apt to lead an inex- 

 perienced observer into error, owing to the fact that light reflected 

 into the eye from white objects, such as white-washed walls, white 

 clothing, etc., causes the formation of white images within the in- 

 terior of the eye. 



The presence of cataract may be tested — under ordinary circum- 

 stances — by holding upright a lighted candle in front of the sus- 



