y54 PRACTICAL PHYSIOLOGY. [LXiV. 



LESSON LXXV. 



OPHTHALMOSCOPE— INTRAOCULAR PRESSURE— 

 PICK'S OPHTHALMOTONOMETER. 



The Ophthalmoscope. — Two methods are employed, and the 

 student must familiarise himself with both, by examining the eye of 

 another person, or that of a rabbit, or an artificial eye. 



1. Direct — givmg an upright image. 



2. Indirect — giving an inverted image. 



A. Human Eye. — (i.) Direct Method. 



(a.) About twenty minutes before the examination is commenced, 

 instil a drop of solution of sulphate of atropine (2 grains to the 

 ounce of water) into, say, the right eye of a person with normal 

 vision. The pupil is dilated and accommodation for near objects 

 is paralysed, owing to the paralysis of the cihary muscle. The 

 patient is seated in a darkened room, and the observer seats himself 

 in front of him, and on a slightly higher level. Place a brilliant 

 light, obscured everywhere except in front, on a level with the left 

 eye of the patient. 



(b.) The observer takes the ophthalmoscope mirror in his right 

 hand, resting its upper edge upon his eyebrow, holds it in front of 

 his own eye, looking through the central hole in it, and directs a 

 beam of Ught into the observed eye, when a red glare — the reflex 

 — is observed. The patient is told to look upwards and inwards, 

 which is conveniently accomplished by telling liim to look to the 

 little finger of the operator's right hand. The operator then 

 moves the mirror, with his eye still behind it, and looks through 

 the hole until the mirror is within two to three inches from the 

 observed eye, taking care all the time that the beam of light is 

 kejjt steadily thrown into the eye. If the eyes of the observer 

 and patient be normal, the observer has simply to relax his 

 accommodation, i.e., look as it were at a distant object, when the 

 retina comes into view as an erect or upright object. 



(c.) Observe the ndinal blood-vessel s running in different direc- 

 tions on a red ground. Move the mirror about to find the optic 

 disc, with the central artery emerging from it. Trace the course 

 of the veins accompanying the arteries across the disc. 



(2.) The Indirect Method, giving an inverted image. 



(a.) The patient, the hght, and the observer are as before. 



