THE SPECIAL SENSES 131 



more convex, mainly by bulging forward, since it meets 

 with less resistance in that direction. This is the power 

 of accommodation for near vision and varies greatly in 

 its range in different people and at different ages. The 

 near point is closest to the eye in youth and increases 

 rapidly with age. At ten it is less than three inches, 

 while at sixty it is more than a yard a distance at 

 which moderate print can not be read. There is 1 prac- 

 tically no far point. Distant objects are visible in pro- 

 portion to their size. But the nearest point at which 

 the rays of light are parallel may be called the distant 

 point. 



A normal eye is called emmetropic. An abnormal eye, 

 not one affected by acute disease, may be myopic, hyper- 

 metropic or presbyopic. 



It has been stated that if the lens is too convex 

 1he focal point will fall closer to the lens. The rays 

 would then form a cone and, if they are not intercepted, 

 disperse again forming a second cone whose apex would 

 begin at the apex of the first cone. This would result 

 in diverging rays striking on the retina and an indis- 

 tinct image. The same result would follow if the retina 

 were too far from the lens, i.e., if the eye were too long. 

 This is actually the case in the myopic or near-sighted 

 eye. The latter name indicates that, to get a clear 

 image, the object must be brought nearer the eye so 

 that divergent instead of parallel, rays may be thrown 

 on the lens. Glasses which break up the parallel into 

 diverging rays would, therefore, correct this defect. 

 Children are not usually born myopic but have, or 

 acquire, perhaps more frequently the latter, weakness 

 of the coats of the eyeball which give way under the 

 strain of reading by bad light or in improper positions 

 and the eye becomes too long. 



