. Refraction and motility of the eye, with chapters on color blindness and the field of vision . by — 2 in one meridianand by — 4 in the other, there is evidently 2 D. of astigma-tism, while to the myopia of — 2 sph. must be added adioptre for the distance at which we are working, so that theeye would be made emmetropic by a — 3 3 — 2 cyl. The correction in mixed astigmatism is estimated inthe same way. The light in one meridian passes from theeye in convergent rays, while that in the other is divergent;consequently the reflex moves with the mirror in one andagainst in the other. Each should b
. Refraction and motility of the eye, with chapters on color blindness and the field of vision . by — 2 in one meridianand by — 4 in the other, there is evidently 2 D. of astigma-tism, while to the myopia of — 2 sph. must be added adioptre for the distance at which we are working, so that theeye would be made emmetropic by a — 3 3 — 2 cyl. The correction in mixed astigmatism is estimated inthe same way. The light in one meridian passes from theeye in convergent rays, while that in the other is divergent;consequently the reflex moves with the mirror in one andagainst in the other. Each should be estimated separately,adding one dioptre to the minus glass and subtracting one 104 REFRACTION AND MOTILITY OF THE EYE. from the plus. The correcting glass is estimated by com-bining the two. If the vertical reflex is with the mirror and reversed bya + 2, the refraction in that meridian is + 1 axis 180, andif the lateral motion is against the mirror and reversed by—12, the refraction in that meridian would be ?— 3 axis 90,and the two may be combined in either of three ways:. Fig. 62. (+ 1 ax. 180 C —3 ax. 90), (—3 sph. C -f 4 ax. 180),(+ 1C-4 axis 90). Eetinoscopy is by far the most generally useful andaccurate method of estimating the refraction of an eye, andwith comparatively little practice the beginner can make anapproximate estimate of the conditions present. But thedetermination of the exact point of reversal, the exact axisof astigmatism, in other words, the estimation of refractionto the fraction of a dioptre which is advisable in manycases, is a much more difficult matter. For this reason thestudent is strongly advised to purchase one of the artificial RETINOSCOPY. 105 e)Tes on the market and practice assiduously (Fig. 62).By aid of one of these he can artificially create an eye withany variety of ametropia and study the movement of thereflex and the adjustment of suitable lenses. It is veryprobable that some persons have a special aptitude for them
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Keywords: ., boo, bookcentury1900, bookdecade1920, booksubjecteye, bookyear1920
