. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, ixed Astigmatism.—Vertical vessels seen with+ 2 S. and horizontal vessels seen with —3 S. would equal— S. O + 5-00 cyl. axis 90 degrees. 14. Diagnosis of the Character of the Refraction bythe Indirect Method (see Fig. 135 and p. 98).—Tliere isnothing exact about this method, and the refractive error,to be recognized, must be considerable. 1. Gradually withdrawing the lens (objective) from infront of the eye, if the aerial image of the disc retains itsuniform size in
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, ixed Astigmatism.—Vertical vessels seen with+ 2 S. and horizontal vessels seen with —3 S. would equal— S. O + 5-00 cyl. axis 90 degrees. 14. Diagnosis of the Character of the Refraction bythe Indirect Method (see Fig. 135 and p. 98).—Tliere isnothing exact about this method, and the refractive error,to be recognized, must be considerable. 1. Gradually withdrawing the lens (objective) from infront of the eye, if the aerial image of the disc retains itsuniform size in one meridian, it signifies emmetropia for thatmeridian ; but if it grows smaller in one meridian, thatmeridian is hyperoj)ic ; or if larger, then that meridian ismyojiic. 2. If the image grows smaller, but more so in one meridianthan the other, it signifies compound hyperopia. If theimage grows larger, but in one meridian more so than theother, then the condition is one of compound myopia. The ASTICMATISM. 153 image growing smaller in one meridian, while in the otherit grows larger, indicates mixed ¥lG. 135.—Companion picture to figure 84. Illustrating the indirect from the lamp (L) are reflected convergently from the mirror of theophthalmoscope, and, passing through the convex lens and into the eye,produce a large retinal illumination, extending from I to I. TB are raysfrom the edge of the disc, and, leaving the eye parallel, pass through theconvex lens and form an inverted aerial image of the disc at T B. The4-4 S. in the ophthalmoscope magnifies the image T B. 15. The cylinder lens test for astigmatism is describedunder Applied Refraction, page 240. 16. Retinoscopy is described in chapter vi. CHAPTER , or the Shadow Test.—This may be de-
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