28 



THE FUNDUS OCULI OF BIRDS 



Fig. 16 



Indirect Ophthalmoscopy 

 Diagram showing the course of the light rays from the lamp, L, to the ophthalmoscopic mirror, 

 00, whence they are reflected to a focus, at F, where they diverge, to be once more focused by the 

 lens on to the retina at Zy, to be finally reflected to the eye of the observer at the opening in 

 the centre of the mirror, 00. 



lamp, L, to the ophthalmoscope mirror, 00, 

 which focuses the rays at F. These sub- 

 sequently divergent rays are now made paral- 

 lel by the convex lens and are thus brought to a 

 focus on the retina-choroid by the dioptric 

 apparatus of the observed eye. Thence the 

 reflected and emergent rays follow the same 

 path and come to a focus, at X, in the eye of 

 the examiner who will see an inverted aerial 

 image of the observed fundus. 



The electric self-illuminating ophthalmo- 

 scope differs from the types just pictured in 

 that it carries its own light source — a bat- 



tery in the handle. It is peculiarly adapted 

 to the examination of the eyes of animals 

 other than Man. One is enabled through 

 this improvement not only to dispense with 

 the cumbersome side light but to make satis- 

 factory examinations of the fundus oculi in 

 only partially darkened surroundings — seri- 

 ous considerations in doing field work with 

 wild species. A picture of the latest model 

 of the self-luminous ophthalmoscope is shown 

 in Fig. 21. 



The fact that a considerable portion of the 

 light thrown into the interior of the eye 



Fig. 17 



Direct Ophthalmoscopy 

 Diagram showing the course of the light rays from the lamp, L, to the mirror, 00, 

 whence they are reflected directly upon the observed retina at BooB. Thence they are 

 reflected through the opening in the mirror, 00, to the observer's eye at E. 



