DISEASES OF THE EYE AND ITS APPENDAGES 117 



exudation into tlie anterior cliamljer, which at once distinguishes the 

 disease from simple ophthahnia. 



During the progress of periodic ophthalmia various changes take place. 

 The swelling of the eyelids and the congestion of the conjunctiva gradually 

 decrease. The amber tint, which at first extended over the whole of 

 the cornea, becomes concentrated at the lower part, owing to the deposit 

 of lymph gradually falling to the bottom of the chamber. In a week 

 or two the whole of the eye begins to become clear, and in from three 

 to six weeks there may be no trace of the disease left, and the organ is 

 to all appearance sound. This condition may possibly continue for the 

 space of a month, or sometimes much longer, but a recurrence of the 

 attack is a matter of certainty. Generally the disease reappears in the 

 same eye, but occasionally the eye originally attacked remains apparently 

 healthy and the opposite eye becomes affected, the course of the disease in 

 it being as nearly as possible identical with that which has been described. 



Probably owing to peculiarities in the system of the horse, the disease 

 at different times assumes an extremely acute, or a sub-acute, or chronic 

 form. In some instances it appears to be concentrated in the eye first 

 attacked, which suffers from repeated reappearances of the disease at short 

 intervals, each attack leaving some morbid changes behind it affecting the 

 internal structures, and ending in total blindness of the affected eye, either 

 from the opacity of the crystalline lens or from the deposit of a large 

 quantity of inflammatory material in the anterior chamber, and ultimately 

 the formation of a false membrane lining the inside of the cornea causing 

 a permanent yellow opacity. In this case it is impossible to ascertain what 

 may be the condition of the structures behind the iris, but post-mortem 

 examinations in a few cases have shown that the whole of the internal 

 structures are implicated in the changes which are apparent in the front 

 of the eyes, the vitreous body and the crystalline lens being the seat of the 

 same kind of yellow deposit which occurred in the anterior chamber. 



In some instances black pigment spots are noticed in front and towards 

 the outer margin of the lens. These indicate that the iris has been 

 adherent to the lens as a result of the inflammatory attack, and the 

 pigment behind the former has been left on the latter. Sometimes the 

 two remain permanently united. 



When periodic ophthalmia was much more common than it is in the 

 present day, it was a matter of observation that if the disease assumed the 

 acute form, and repeated attacks occurred in one eye, ending in blindness, 

 the other eye remained unaffected; but when the affection appeared first 

 in one eye and then in the other, alternately, the result was the gradual 

 impairment of the vision until the sight was entirely lost in both. 



