THE OPHTHALMOSCOPE. 



161 



keeping it always in the same line, until when you are about 

 two or three inches away from the subject's eye the bright spot 

 of the retina comes clearly into view. Both observer's and sub- 

 ject's eyes must be unaccommodated. 



Indirect Method. The arrangement is as before except that 

 a converging lens is held two or three inches away from the 

 observed eye and steadied by resting a finger of that hand 



FIG. 45. Diagrams to illustrate the use of the retinoscope. No. 1 shows the path of rays 

 from a normal eye, No. 2 that for rays from a normal eye in front of which is held a converging lens, 

 or of rays from a shortsighted eye. 



against the subject's forehead. Hold the ophthalmoscope 

 about twenty inches away and move it about and move the 

 lens back and forth until the image of the bright spot is clearly 

 seen. The observer must accommodate his eye for a point near 

 at hand. 



THE RETINOSCOPE. Another instrument which is used to examine the 

 refraction in the eye is the retinoscope, a flat mirror with a little peep-hole in the 

 middle, which can be made to rotate through a small angle on its handle. The 

 principle of its use depends on the following considerations. If a spot of light is 



