198 OPHTHALMOLOGY FOR VETERINARIANS 



mirror vertically and horizontally. If the reflection cast 

 upon the retina moves in the same direction as the 

 movement of the mirror, the animal is hyperopic. If 

 the reflection moves in the opposite direction from that of 

 the mirror, the animal is myopic. If the reflection moves 

 with in one meridian and against in the other, mixed 

 astigmatism is present. If it moves with in one meridian 

 and not at ah in the opposite meridian, astigmatism is 

 present. If it moves against in one meridian and not 

 at all in the opposite meridian, astigmatism is also 

 present. In man, the correction is made by placing 

 lenses, either plus or minus, before the eye until one is 

 found that will neutralize the movement of the reflec- 

 tion. When the movement is with, plus lenses are used; 

 and when it is. against, minus lenses are used. Com- 

 pound errors are determined when the movement of the 

 same character is greater in one meridian than in the 

 opposite meridian. 



In order to get a perfect correction one must control 

 the action of the ciliary muscle by the use of a cyclo- 

 plegic. Atropin in i per cent, solution or homatropin in 

 2 per cent, solution may be used. The former may be 

 used three times a day for a few days before examina- 

 tion, while the latter has its maximum effect in about an 

 hour's time. It will be necessary to drop this into the 

 eye every ten minutes for an hour at least. The effect 

 of this gradually wears away, so that the animal can 

 accommodate its vision in twenty-four to forty-eight 



