DISEASES OF THE EYE. 411 



As a general rule, after several attacks of ophthalmia the pupil dilates 

 aud clears, and cataract forms. But in special cases the pupil may re- 

 main constantly contracted, because adhesion has taken place between 

 the capsule of the lens and the iris ; or, on the other hand, the pupil may 

 remain abnormally open, if there is paralysis of the optic nerve or a ten- 

 dency to amaurosis. In such a case the eye is more tolerant of light, 

 because less susceptible of its effect. 



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. 



Spurious cataracts consist of an effusion of lymph into the posterior 

 chamber of the eye, perhaps adherent against or upon the anterior surface 

 of the lens. The lens itself is not really affected. Flakes of white lymph 

 are also sometimes seen in the aqueous humour in the anterior chamber. 

 These, if they do not become adherent, are usually soon absorbed. 



848. Examination of the Eye for Cataract. 



The state of the pupil is best seen in a diminished light. The existence 

 or otherwise of cataract, the proper motion of the iris, and the state of 

 the structures of the eye generally, are then as a rule very easily observed. 

 But in some cases it is advisable to take the horse into a darkened 

 stable and to examine his eye by the light of a candle, when the pupil 

 will be found to be fully expanded. 



In health, when a candle is moved before the fully expanded pupil, 

 three images of it will be seen. First an erect image moving upwards 

 and downwards, according as the candle is moved. This image is pro- 

 duced by reflection from the surface of the cornea. Secondly, another 

 erect image produced from the anterior surface of the lens ; this also 

 moves upwards and downwards, according as the candle is moved. 

 Thirdly, a small inverted image reflected from the posterior surface of 

 the lens ; this moves downwards when the candle is moved upwards. 



In lenticular cataract, in the early stage, the inverted image is indis- 

 tinct. In its later stage it cannot be seen at all. When the cataract 

 has fully formed, the deep erect image is invisible. In capsular cataract 

 only the front image is visible. 



849. Lenticular Cataract. 



Lenticular cataract, or in other words partial or complete opacity of 

 the lens, is the result of the deposits left by repeated attacks of inflam- 

 mation. The effusion is at first interspersed through the substance of 

 the lens, but gradually, as the more watery parts of the effusion are taken 

 up, the deposit concentrates to one spot and forms the opaque speck 

 known as cataract. Cataracts are generally of very gradual formation. 

 The first attack of inflammation, though it probably leaves some, yet 

 generally gives rise to no perceptible deposit or opacity ; but after several 

 attacks the deposit or speck becomes apparent. 



In old horses similar changes sometimes go on insensibly, ending in 



