. Refraction and motility of the eye, with chapters on color blindness and the field of vision . oportion to the amount of myopia. At the apex of thecone, where the rays of light cross, an aerial image is formedof the illuminated area on the retina, which the observersees instead of the area itself. Now if the top of themirror be tilted forward, the illumination on the retina RETINOSCOPY. 95 travels downward and the emergent cone of rays is directedupward, but to the observer the aerial image at the apex ofthe cone appears to have moved upward, or against hismirror. If the bottom of the mirror
. Refraction and motility of the eye, with chapters on color blindness and the field of vision . oportion to the amount of myopia. At the apex of thecone, where the rays of light cross, an aerial image is formedof the illuminated area on the retina, which the observersees instead of the area itself. Now if the top of themirror be tilted forward, the illumination on the retina RETINOSCOPY. 95 travels downward and the emergent cone of rays is directedupward, but to the observer the aerial image at the apex ofthe cone appears to have moved upward, or against hismirror. If the bottom of the mirror be tilted forward, theilluminated area on the retina actually moves upward, theemergent cone is directed downward, and the aerial imageappears to have moved downward. The same is true of thelateral movements, and if the myopia is high, the aerialimage can move through a considerable arc before dis-appearing from view. In myopia, then, the apparentmotion of the reflex is opposite or against that of themirror, while the reflex is dim and the motion slow in pro-portion to the amount of Fig. 58. Xow let us consider a very low myopia of one of light from the mirror do not form very largediffusion rings and therefore the reflex is comparativelybright. The emergent rays are slightly convergent, forminga slender cone of light whose apex is exactly forty inchesfrom the nodal point of the eye. If, now, the observerstations himself at, say, a distance of twenty inches fromthe eye, or inside the crossing point of the rays, and tiltsthe top of his mirror forward, the illuminated area movesdownward, the emergent cone is directed upward, and theobserver, since he is within the crossing point of the rays,sees the reflex itself, which therefore appears to moveexactly as in hyperopia and emmetropia. If he graduallyincreases his distance from the patients eye, the motion 96 REFRACTION AND MOTILITY OF THE EYE. continues to be with his mirror as long as he can see thereflex l
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Keywords: ., boo, bookcentury1900, bookdecade1920, booksubjecteye, bookyear1920
