Ocular refraction and the shadow test . An emmetropic eye adapted for distance, the divergent rays represented by dotted lines,form circles of diffusion upon the retina their focus being behind the retina. but at the point P back of it. The rays from the object at P formcircles of diffusion upon the retina and the object does not Figure An emmetropic eye adapted for a near point. The parallel rays, represented by dotted linesform circles of diffusion upon the retina, their focus being in front of the retina. Figure 98 represents the eye adjusted for the object P. Parallelray
Ocular refraction and the shadow test . An emmetropic eye adapted for distance, the divergent rays represented by dotted lines,form circles of diffusion upon the retina their focus being behind the retina. but at the point P back of it. The rays from the object at P formcircles of diffusion upon the retina and the object does not Figure An emmetropic eye adapted for a near point. The parallel rays, represented by dotted linesform circles of diffusion upon the retina, their focus being in front of the retina. Figure 98 represents the eye adjusted for the object P. Parallelrays from distant objects enter the eye at the same time but arebrought to a focus at F, a point in front of the retina. The dottedlines represent rays from the distant object, they meet and cross at 114 OCULAR U E F R A C T 1 O X. the point F, then diverge and reach the retina lo form circles of iffu-sioD, and therefore no distinct image. // is thus demonstrated, that the eye sees clearly, only those objectslying in the /lane for ivhick it is at the instant adjttsted. In looking about a room of average size, in looking at objectswithin ones reach, in reading, etc., it is seen that the accommodationmust be constantly in action. The more we know of this wonderfulfunction of the eye, the more marvelous we find it to be. Our visualcomfort is larg
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