866 



THE SENSE OF SIGHT 



hypermetropia.i 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'^ B^;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 inL^ 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^ andFJ5, illuminate the retina 

 of P by a diffusion circle A^B^; 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^ 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. 



