REFRACTION IN THE EYE 479 



MEASUREMENT OF ACCOMMODATION 



Far Point. The most distant point of which 

 the eye at rest, i. e. the ciliary muscle entirely 

 relaxed, can form a clear image on the retina was 

 termed by Bonders the far point (punctum re- 

 motum = r). The distance of r from the eye 

 = H. In the emmetropic eye parallel rays are 

 brought to a focus on the retina ; r is theoret- 

 ically at an infinite distance. Practically, if the 

 accommodation be kept at rest by voluntarily re- 

 laxing the ciliary muscle or by paralyzing the in- 

 ner vation of the muscle with atr opine, the far 

 point will be found at twelve metres, at which 

 distance objects produce dispersion circles so 

 small as to cause no perceptible lack of clearness 

 in the image* 



In the myopic eye, r is a short distance in front 

 of the eye. 



In hypermetropia, only convergent rays can be 

 focussed on the retina of the eye at rest. Parallel 

 and divergent rays can be focussed only by use 

 of the accommodation mechanism ; r is therefore 

 negative. 



Determination of Far Point. Place the subject 

 in a well-lighted room six metres in front of a 

 card of Saellen's test-types. At this distance the 



