DISEASES OF THE EYE. 263 



stall, or to the reflection from snow or water, is undoubtedly injurious. 

 The unprotected exposure of the eyes to sunshine through the use of 

 a very short overdraw check is to be condemned, and the keeping of 

 the horse in a very dark stall from which it is habitually led into the 

 glare of full sunlight, intensified by reflection from snow or white 

 limestone dust, must be set down among the locally acting causes. 

 But exposure to cold and wet, to wet and snow storms, to cold drafts 

 and wet lairs must also be accepted as causes of conjunctivitis, the 

 general disorder which they produce affecting the eye, if that happens 

 to be the weakest and most susceptible organ of the body, or if it has 

 been subjected to any special local injury, like dust, irritant gases, 

 or excess of light. Again, external ophthalmia is a constant con- 

 comitant of inflammation of the contiguous and continuous mucous 

 membranes, as those of the nose and throat. Hence the red, watery 

 eyes that attend on nasal catarrh, sore throat, influenza, strangles, 

 nasal glanders, and the like. In such cases, however, the affection 

 of the eye is subsidiary and is manifestly overshadowed by the pri- 

 mary and predominating disease. 



Symptoms. — ^The symptoms are watering of the eye, swollen lids, 

 redness of the mucous membrane exposed by the separation of the 

 lids — it may be a mere pink blush with more or less branching red- 

 ness, or it may be a deep, dark red, as from effusion of blood — and a 

 bluish opacity of the cornea, which is normally clear and translucent. 

 But except when resulting from wounds and actual extravasation of 

 blood, the redness is seen to be superficial, and if the opacity is con- 

 fined to the edges, and does not involve the entire cornea, the aque- 

 ous humor behind is seen to be still clear and limpid. The fever is 

 always less severe than in internal ophthalmia, and only runs high in 

 the worst cases. The eyelids may be kept closed, the eyeball retracted, 

 and the haw protruded over one-third or one-half of the ball, but this 

 is due to the pain only and not to any excessive sensibility to light, as 

 shown by the comparatively widely dilated pupil. In internal oph- 

 thalmia, on the contrary, the narrow contracted pupil is the measure 

 of the pain caused by the falling of light on the inflamed and sensitive 

 optic nerve (retina) and choroid. 



If the affection has resulted from a wound of the cornea, not only 

 is that the point of greatest opacity, forming a white speck or fleecy 

 cloud, but too often blood vessels begin to extend from the adjacent 

 vascular covering of the eye (sclerotic) to the white spot, and that 

 portion of the cornea is rendered permanently opaque. Again, if the 

 wound has been severe, though still short of cutting into the anterior 

 layers of the cornea, the injury may lead to ulceration that may pene- 

 trate more or less deeply and leave a breach in the tissue which, if 

 filled up at all, is repaired by opaque fibrous tissue in place of the 



transparent cellular structure. Pus may form, and the cornea assumes 

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