REFRACTION IN THE EYE 491 



that the inner tube of the artificial eye. is drawn 

 out to the line marked zero upon its scale ; the 

 eye is then accommodated for distant vision. Set 

 the eye at the level of the observer's eye and 

 near the edge of the table. Place the light on the 

 right side of the artificial eye and slightly behind 

 it. Hold the ophthalmoscope in the right hand 

 close to the right eye at a distance of about fifty 

 centimetres from the artificial eye, and look 

 through the aperture in the mirror. The elbow 

 should be close to the side. The head should 

 be vertical so that the observer's eye and the 

 artificial eye may have the same visual axis. 

 Keep the reflected light upon the pupil of the 

 artificial eye. It will be illuminated by the red 

 reflection from the choroid coat. With the pupil 

 illuminated, approach the artificial eye until the 

 lens-bearing disk lies in the anterior principal 

 focus (50 mm. in front of this eye, 13 mm. in 

 front of the cornea of the normal human eye; 

 seepage 494.) The artificial eye is accommodated 

 for distant objects. The observer's eye must also 

 be accommodated for distant vision. The power 

 of voluntarily relaxing the ciliary muscle is at- 

 tained by practice ; the observer should endeavor 

 to look through and beyond the eye at some dis- 

 tant object. If the observer be myopic or hyper- 

 metropic, his refractive error should be corrected 



