DISEASES OF THE EYE AND ITS APPENDAGES 109 



DISEASES OF THE EYE AND ITS APPENDAGES 



It is perhaps impossible to overestimate the importance of perfect 

 soundness of the eyes of a horse. The extreme inconvenience of a slight 

 defect is very apparent to a rider or driver of an animal which is in the 

 habit of shying when, so far as can be seen, there is nothing to attract 

 particular attention. 



Unfortunately, even important defects of vision may be attended with 

 such obscure signs as to be absolutely undiscoverable by the ordinary 

 methods of examination which are at the command of an amateur. The 

 use of the ophthalmoscope by an experienced and highly accomplished 

 observer is often necessary for their detection. In the horse, slight 

 errors in refraction cannot be found out even by an expert, and if they 

 could, there is no remedy, because the optical appliances, which are so 

 valuable in compensating even the least departure from perfectly normal 

 vision in man, are inapplicable to any of the lower animals. 



Obviously the examiner of a horse's eyes will be quite unable to distin- 

 guish some of the marked departures from the healthy state unless he has 

 some acquaintance with the eye in its natural condition. With this view 

 the reader is referred to the section on the anatomy and physiology of the 

 eye. Meanwhile he is cautioned that the most ludicrous mistakes are made 

 by persons who, in looking for diseased conditions of the eye of the horse, 

 have not taken the trouble in the first instance to master the normal 

 appearances which can be readily seen without the use of any optical 

 apparatus. 



EXAMINATION OF THE EYES 



For the purpose of making an examination of the eye, the horse should 

 be so placed by the observer that the light may fall on the organ either 

 from a window or from the stable entrance, while the animal's head is 

 either within the stable or only partly out of it. In this position the 

 examiner will naturally first note the condition of the eyelids and the 

 movements of the eye. If, during this time, the animal happens to be 

 suddenly alarmed, even by the movement of a hand towards the eye, he will 

 also witness the rapid protrusion of the haw (fig. 247) (cartilago nictitans) 

 over the front of the organ, as if to protect it from injury. In the section 

 on anatomy and physiology the structure and uses of this organ are 

 described. 



Having the eye in a good light, the examiner will note the white portion 

 of the globe, with its numerous vessels ramifying in all directions, and the 



