12 EXAMINATION OF HORSES 
can make out, independently of the structures I have 
named. 
The oblique or focal illumination is the readiest and 
best way of examining the anterior half of the eye. 
By its aid we are enabled to examine, with great 
minuteness, the appearances presented by the cornea, 
iris, pupil, lens, and even the most anterior portion 
of the vitreous humour. <A candle or small lamp, and 
an ordinary pocket lens of from two-and-a-half to 
four-inch focus, is all we require. The light is held 
in front and to one side of the eye, at a distance of 
about a foot to eighteen inches, and on a level with 
the eye; the flame is then brought to a focus with 
the lens, and thrown first on the cornea, then on the 
iris and crystalline lens; the examiner’s eye, being 
placed on the opposite side, in front of the horse’s 
eye, catches the rays emanating from the latter. By 
shifting the cone of light from one portion of the 
cornea or lens to another, we may rapidly, yet 
thoroughly, examine its whole expanse, and detect . 
the slightest opacity. Opacities of the cornea or lens 
appear by this reflected light of a light grey or whitish 
colour. 
The catoptric test is a very useful one in diagnosing 
cataract, and had better be used along with the oblique 
illumination. It is conducted as follows :—A lighted 
candle or taper is moved before the eye. If the organ 
be healthy, three images of the light are seen. Two 
of these images are erect, the third is inverted. The 
