. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, Fig. 140.—.^utliors IrisDiaphragm Chimney. 158 REFRACTION AND HOW TO REFRACT, and fall upon the mirror held before the right eye. Somesurgeons prefer having the light, with the 3 cm. opening inthe screen, placed over the patients head or to one side ofit. (Fig. 141.) TJic distance bctzvcoi the ligJit and mirrorwill not alter the direction of tJie rays of light which conicfrom the patients eye. Position of the Light and the Concave Mirror (, 142, 143).—As the pur
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, Fig. 140.—.^utliors IrisDiaphragm Chimney. 158 REFRACTION AND HOW TO REFRACT, and fall upon the mirror held before the right eye. Somesurgeons prefer having the light, with the 3 cm. opening inthe screen, placed over the patients head or to one side ofit. (Fig. 141.) TJic distance bctzvcoi the ligJit and mirrorwill not alter the direction of tJie rays of light which conicfrom the patients eye. Position of the Light and the Concave Mirror (, 142, 143).—As the purpose of the concave mirror inretinoscopy is to focus rays of light before they enter the. I METER Fig. 141.—Light over Patients Head, and the Observer with Mirror at OneMeter Distance. patients eye, it is always necessary to have the light andmirror widely separated. Usually, the light with the 3 in the screen is placed to one side or over the pa-tients head, and the surgeon with the mirror is seated aboutone meter from the patient. This will place the focus of the25 cm. mirror at about 33 cm. in front of the of Surgeon from Patient.—With the plane mirror he may approach w ilhin a few inches of the patientseye to fintl the point of reversal, hut with the concaxe minor RETINOSCOPY. 159 he must remain at a sufficient distance to have the focus ofthe mirror in front of the patients eye. How to Use the Mirror.—It should be held firmly in
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