866 



THE SENSE OF SIGHT 



hypermetropia. x Astigmatism may also be detected and corrected in this way. 

 In order to form an idea regarding the meridians in which the refraction is defect- 

 ive, we only need to observe the retinal blood-vessels along the horizontal and 



FIG. 465. DIRECT OPHTHALMOSCOPY. 



Diagram to illustrate the remittance of the rays of light by the myopic eye. O, 

 observer's eye; M, mirror; P, patient's eye; F, the rays FA and FB illuminate the 

 retina of P by a diffusion circle A 1 B l \L, the rays emitted by this luminous point leave 

 the eye of P convergently and must therefore be rendered divergent by the interposition 

 of a concave lens before they can be focalized in L 1 by the eye of the observer. 



vertical planes of the optic disc (Fig. 438). The latter appears as a nearly round 

 or slightly oval area varying in color from grayish pink to a more decided red. Its 

 center is occupied by a light patch marking more exactly the entrance of the 

 retinal blood-vessels. The circumference of the optic papilla appears as a dark, 



FIG. 466. DIRECT OPHTHALMOSCOPY. 



Diagram to illustrate the remittance of the rays of light by the hypermetropic eye. 

 O, observer's eye; M, mirror;P, patient's eye ;F, the raysF^l and FB/illuminate the retina 

 of P by a diffusion circle A 1 B 1 ;L, the rays emitted by this luminous point leave the eye 

 of P divergently and must therefore be rendered convergent by the interposition of a 

 convex lens before they can be focalized inL 1 of the eye of the observer. 



usually incomplete ring representing the border of the choroid coat. Within this 

 lies a faint white line, indicative of the brim of the sclerotic coat. 



1 If the observer is ametropic and does not employ the necessary glasses during 

 this examination, he must of course make this additional correction. 



