RANGE OF DISTINCT VISION 



68l 



e and / are focused at a single point on the ret!na nn. If the needle be brought 

 nearer than the near-point, the strongest effort of accommodation is not 

 sufficient to focus the two pencils, they meet at a point behind the retina. 

 The effect is the same as if the retina were shifted forward to mm. Two 



FIG. 461. Diagram of Experiment to Ascertain the Minimum Distance of Distinct Vision. 



images, h, g, are formed, one from each hole. It is interesting to note that 

 when in this way two images are produced, the lower one, g, really appears in 

 the position Q, while the upper one appears in the position P. This may be 

 readily verified by covering the holes in succession. 



FIG. 462. Diagram of the Axes of Rotation of the Eye. The thin lines indicate axes of 

 rotation, the thick the position of muscular attachment. 



During accommodation two other changes take place in the eyes. The 

 eyes converge by the action of the extra-ocular muscles, chiefly by the internal 

 and inferior recti or internal and superior recti. The pupils contract. 



