VISION. 



FIG. 46. Use of Ophthalmoscope. Direct 

 method. S, eye of subject ; , eye of observer; 

 M, mirror ; L, source of light. 



directly upon the enlarged and upright details of the fundus. In 

 the indirect, the subject is at an arm's length, and a convex lens is 

 placed between the sub- 

 ject's eye and the exam- 

 iner's mirror. The image, 

 as obtained, is inverted 

 and aerial. The two 

 methods differ, practi- 

 cally, in that the direct 

 image is larger and erect, 

 in a small field, while the 

 indirect image is smaller 

 and inverted, but in a 

 larger field. The two 

 methods are explained in 

 the accompanying figures 

 (46 and 47). 



Examine the fundus, both by the direct and indirect method, 

 and make an outline drawing showing the disc and retinal vessels 

 in each case. 



PERIMETRY. 



In contradistinction to visual acuity which is limited to the 

 macula, the function of sight performed by the other parts of the 

 retina is called indirect vision. 



The limits of the field of vision are best obtained by an instru- 

 ment, the perimeter, but a fairly accurate map of a field, not larger 

 than 45, may be obtained on a blackboard. 



Exercise. In the centre of the blackboard, in the line of direct 

 vision, locate a dot, the point of fixation. Draw from the dot, as 

 a centre, a series of circles whose distance from each other shall 

 represent an angular distance of 10. 



Now draw the meridians which will divide each quadrant into 

 at least three subdivisions. 



A wooden guide, twenty centimetres long, should be provided 



