8 4 8 



ILLUMINATION OF THE EYE, AND THE OPHTHALMOSCOPE. 



The simple apparatus shown in Fig. 292 is sufficient to corroborate what 

 has been said: Let B represent the eye to be examined, and A the eye of the 

 observer. If a flame be placed at x, its rays will be thrown upon the glass plate 

 5 5, which reflects them in the direction of the dotted lines into the eye B. The 

 eyeground appears in this position brightly illuminated around b in diffusion- 

 circles. As the observer A can see through the glass plate 5 5 without difficulty, 

 and in the same direction as the reflected ray x y, he will see the retina brightly 

 illuminated at b. 



FIG. 



FIG. 294. 



FIG. 295. 



It is important for practical purposes to be able to recognize the 

 etails of the eye-ground : the blood-vessels, the macula lutea, the optic- 

 nerve entrance, abnormalities of the retina, of the choroidal pigment, 

 and the like. How this is to be done will be understood from the 

 following considerations: As has been seen (and as Fig 279 p 829 

 shows) a small, inverted image is formed on the retina (c d] of an object 

 (A &) tor which the eye is accommodated. Conversely, according to the 



