864 



THE SENSE OF SIGHT 



lamp adjusted laterally to his head. Since the constriction of the 

 iris would seriously interfere with this examination, this mechanism 

 is temporarily paralyzed by means of atropin. Some mirrors are 

 equipped with a small electric lamp (Dennett's or Marple's modifica- 

 tion) which enables us to examine the eyes of bedridden patients and 

 also obviates in a measure the use of atropine.^ In the center of the 



Fig. 463. — Loring's Ophthalmoscope, with Tilting Mireok, Complete Disc of 

 Lenses from — 1 to — 8 and to + 7, and Supplemental Quadrant Containing ± 

 0.5 AND ± 16 D. This Affords 66 Glasses or Combinations from + 23 to — 24 D. 



reflecting mirror is a small opening which is adjusted directly in front 

 of the pupil of the observer's eye. We may then follow either the 

 direct or the indirect method of ophthalmoscopic examination. 



The Direct Method. — If the eye of the observer is not emmetropic, it should 

 first be made so by spectacles (Fig. 464). The mirror (w) is held close to the ob- 

 served eye, so that the rays reflected from it are able to spread out widely upon the 

 opposing retina {A'B'). The area of the retina so illuminated remits rays (L) 

 which traverse the dioptric media of this eye and are sent outward into space. 

 Now, it is evident that thie emmetropic eye remits these rays parallel to the visual 



^ Large ophthalmoscopes have been constructed by Gullstrand and others. 

 The first gives a magnification of 5 to 50 times in monocular and 20 times in 

 binocular vision. Hertzell illuminates the eye by means of an 80 candle power 

 electric lamp placed in the patient's mouth (ophthalmodiaphanoscopy). 



