Transactions . ssible, 113 114 from a causal standpoint, to regard the act of accommoda-tion as an isolated one. When an object is brought closer to the eye than 6 meters,two physical facts follow: in the first place, the visual angleformed at the eye by the rays from the extremities of theobject becomes larger, and this increase is proportionate tothe proximity of the object to the eye. In the second place,the rays of light originating at any point on the surface of theobject, after passing through the dioptric system of the eye nolonger meet at their former focus, but at some point posterior
Transactions . ssible, 113 114 from a causal standpoint, to regard the act of accommoda-tion as an isolated one. When an object is brought closer to the eye than 6 meters,two physical facts follow: in the first place, the visual angleformed at the eye by the rays from the extremities of theobject becomes larger, and this increase is proportionate tothe proximity of the object to the eye. In the second place,the rays of light originating at any point on the surface of theobject, after passing through the dioptric system of the eye nolonger meet at their former focus, but at some point posteriorto it, dependent on the proximity of the object to the of course assumes that the accommodation is inactive. Within certain limits, the size of the visual angle deter-mines the size of the image formed on the retina. Now it isconceivable that as soon as this retinal image has increasedbeyond a certain size, or in other words, as soon as the raysfrom the extremity of an object have formed an image which. Fig. 1 extends over a certain number of rod and cones, a stinuilustravels up the optic nerve to the centers of accommodation,convergence and pupillary contraction, which brings aboutthese acts. While tliis is possibly true for pupillary contrac-tion, it is certainly not true for the other two. Leaving con-vergence out of consideration, if accommodation were evokedby the varying size of the retinal images, the same sizedretinal image should always cause the same amount of accom-modation in the same eye, at least at the same period of this is not true, because the image formed by an object2 feet away from the eye is of the same size as that formed byan object 10 times its size 20 feet away, as shown by tlie dia-gram. In the former case there will be an act of accommoda-tion, while in the latter there will be none. Let AO and BO be rays of light from the extremities of theobject. AB. The AOB will be the visual angle, and BAthe image. But BA will also I:>e the i
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