DISEASES OP THE EYE. 403 



ft40. HAW, COMMON OPHTHALMIA, AND CONJUNCTIVITIS. 



Of diseases resulting from external causes common Ophthalmia or 

 inflammation of the conjunctiva is the most frequent. It usually has its 

 origin in some casual injury, or from the presence of some foreign body. 



Atmospheric causes are an occasional but not very common source of 

 this disease. Most of those cases, which may seem at first sight to arise 

 from atmospheric causes, will be found to be merely an extension to the 

 eye of inflammation already existing in the membrane of the nose. 



841. Symptoms. 



The first noticeable symptom is the closing of the eye, accompanied by 

 a profusion of tears. Unless the seat of injury is wholly external, and 

 therefore at once apparent, the eye should be examined. Here however 

 we at once meet with some difficulty. The animal closes his eyelids 

 firmly. He is impatient of light. As soon as we attempt to separate 

 the lids he withdraws his eye into the socket, and the haw is thereby 

 pushed forwards and the tears flow profusely. A sharp rap of the hand 

 on the neck will sometimes cause the animal to open his eye, and an 

 opportunity to examine it will then be afforded. If this device fails, the 

 hand should be laid steadily on the brow with the thumb resting on the 

 margin of the upper lid. The thumb must be kept quietly and firmly 

 on the lid, until the retractor muscle ceases to act violently, and then 

 the lid should be gently pushed upwards, and the index finger of the 

 other hand may at the same time draw down the lower lid. 



A disturbed state of the blood-vessels and a reddened hue of the con- 

 junctival membrane will probably be noticed. Possibly on further exa- 

 mination we may detect a wound of the cornea, such as that inflicted 

 by a whip or by a bite from another, horse. If however there is no such 

 wound, the chances are that some foreign body, such as a hay seed, has 

 lodged on the eye. The seat of such lodgment is generally under the 

 tipper eyelid. In such cases the removal of the foreign body is of course 

 the primary requisite. The upper eyelid is easily everted with a little 

 tact by pressing against its outer surface with a blunt probe or some such 

 instrument, and turning the margin of the eyelid upwards and inwards at 

 the same time. Foreign bodies seldom lodge on the cornea, because the 

 action of the haw, aided by the flow of tears which are at once effused, 

 speedily carries them away. 



Although blows over the eye or upon it are not usually productive of 

 dangerous symptoms, yet we occasionally find disastrous results. Con- 

 cussion of the retina may take place from the effect of a violent blow on 

 the eye, and may be followed by temporary or permanent amaurosis. 

 Again, the humors of the eye may be lost ; or the rupture may be 

 internal, and we may then have an escape of blood into the anterior 

 chamber of the eye ; or the ciliary margin of the iris may lose its connec- 

 tion, and may afterwards by process of adhesive inflammation become 

 attached to some adjacent structure ; or there may bo displacement of 

 the crystalline lens, which may be driven into the vitreous humor, or it 

 may fall forward into the anterior chamber. When the blow is so violent 



