. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, noted by the position of thecenter of the pupil of the squintingeye over the millimeter line on theinstrument. Each millimeter ofdeviation is supposed to represent5 degrees of deviation. This deviceis not reliable, and is not in commonuse. A more reliable estimate is ob-tained by measuring the deviationon the arc of the perimeter. (SeeFig. 159.) To do this, the patientis seated with the squinting eyeopposite to the fixation point (R)and instructed to look at a distantob
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, noted by the position of thecenter of the pupil of the squintingeye over the millimeter line on theinstrument. Each millimeter ofdeviation is supposed to represent5 degrees of deviation. This deviceis not reliable, and is not in commonuse. A more reliable estimate is ob-tained by measuring the deviationon the arc of the perimeter. (SeeFig. 159.) To do this, the patientis seated with the squinting eyeopposite to the fixation point (R)and instructed to look at a distantobject (R) across the room, so that the object, the fixationpoint, and the squinting eye (R) are in line ; this line repre-sents the direction which the eye would take observer, taking a lighted candle, i)laces it at the fixa-tion point and gradually moves it outward along the innersurface of the arc until his own eye, directly back of theflame, sees an image of the flame at the center of the pupilof the sciuinting eye. The degree mark on the arc fromwhich the Hanie was pictured represents tlic amount ^^i the. MUSCLES. 95 deviation or angle of the strabismus; this angle beingformed by the visual axis with the direction of the normalvisual line. The degree mark on the arc is in front of tiie
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Keywords: ., bookcentury1900, bookdecade1900, bookidref, booksubjecteyeglasses
