. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, Fig. 84. at one time, but it is not so perfect in detail nor is it mag-nified to the same extent as in the direct method. Theobserver does not have to get so close to his patient, whichis a decided advantage in some clinical cases. Unfortun-ately, as a preliminarystep, it is often neces-sary to dilate the pu-pil. In addition tothe ophthalmoscope,there is also requireda convex lens ofknown strength andlarge aperture; theone which comes inthe case with thescope is usual!)
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, Fig. 84. at one time, but it is not so perfect in detail nor is it mag-nified to the same extent as in the direct method. Theobserver does not have to get so close to his patient, whichis a decided advantage in some clinical cases. Unfortun-ately, as a preliminarystep, it is often neces-sary to dilate the pu-pil. In addition tothe ophthalmoscope,there is also requireda convex lens ofknown strength andlarge aperture; theone which comes inthe case with thescope is usual!)- too small and too strong for general writer prefers his plus 13 I), with metal rim and con\-en-ient handle, shown in figure 85 (reduced one-third in size).. Fig. 85. OlH THALMOSCOPE. 99 This is held at about three inches in front of the eyeunder examination, the observer resting his httle and ringfingers on the temple of the patient. The hght may beover the patients head, or to the side corresponding to theeye under examination, the patient being instructed to lookwith both eyes open toward the surgeons right ear whenthe right eye is being examined, and toward the surgeonsleft ear when the left eye is examined. With a +4 D. in the ophthalmoscope held close to hiseye, the surgeon seats himself in front of the patient atabout sixteen inches distant, and reflects the light throughthe condensing lens into the patients eye, and thenapproaches or moves away from the eye until he recog-nizes clearly a retinal vessel or the disc ; he must remem-ber, however, that he is not looking into the eye. but isviewing an aerial image formed between the convex lensand the ophthalmoscope ; this image is not only inverted,but undergoes lateral inversion, so t
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