. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, hat he gets the point of reversal at i meter distance, hewill have the following rule to guide him—/. c. : To add a —i sphere to the dark-room correction, nomatter what that may be. T^^r example : Darkroom, -[ -| -f ., . . — — — — — — Infinity, . .—). — D. — — I). -f I). Application of Retinoscopy in Astigmatism.—If the surgeon has mastered retinoscopy in hyp
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, hat he gets the point of reversal at i meter distance, hewill have the following rule to guide him—/. c. : To add a —i sphere to the dark-room correction, nomatter what that may be. T^^r example : Darkroom, -[ -| -f ., . . — — — — — — Infinity, . .—). — D. — — I). -f I). Application of Retinoscopy in Astigmatism.—If the surgeon has mastered retinoscopy in hyperopia antl myopia,he should not have any difficulty in pursuing exactly the KETINOSCOPV. 167 same course in cases of astigmatism. As already stated, the presence of astigmatism is diagnosed by the presence of a band or ribbon-hke streak of bright illumination which extends across the pupillary area. (See Fig. 147.) This band of light may be seen before any neutralizing lens is placed in front of the eye, if the astigmatism is in excess of the spheric correction, as in the following formula :. sph. O +4-50 cyl. axis 105 degrees.— sph. 3— cyl. axis 165 degrees. Fig. 147.—Band of Axis 90 de-grees. Or the presence of astigmatismmay not be recognized until after a sphere has been placedin front of the eye, as in one of the following formulas : -( sph. 3 + cyl. axis 75 degrees.— sph. 3—i-oo cyl. axis 180 degrees. In refracting cases of astigmatism with the retinoscope,all the surgeon has to do is to refract the meridian of leastametropia first, and tlicii the meridian of greatest the following formula : -) sph. 3 l-i-OO cyl. axis 90 degrees ; in the dark-room a + S. would make all movementcease in the vertical meridian, at one meter distant ; butwhen the mirror is tilted in the horizontal meridian, tiierewould be seen a band of light extending across the pupilon axis 90 degr
Size: 1806px × 1383px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookidref, booksubjecteyeglasses
