. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, ^ emmetropiceyes with the accommodation at rest. Figure 8i shows theposition of the light, L, the ophthalmoscope, the examinersand the examined eye under these conditions. The divergent rays from the light (L) are reflected con-. FiG. 8i. vergently from the concave mirror, and focusing in the vitre-ous, they cross and form an area of illumination on theretina at IF. The retina, situated at the principal focus ofthe dioptric media, naturally projects out from its indi-vi
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, ^ emmetropiceyes with the accommodation at rest. Figure 8i shows theposition of the light, L, the ophthalmoscope, the examinersand the examined eye under these conditions. The divergent rays from the light (L) are reflected con-. FiG. 8i. vergently from the concave mirror, and focusing in the vitre-ous, they cross and form an area of illumination on theretina at IF. The retina, situated at the principal focus ofthe dioptric media, naturally projects out from its indi-vidual points rays of light which are parallel as they leavethe eye ; some of these pass through the sight-hole of themirror and meet upon the retina of the observers emme-tropic eye. There are two very important points which nuist bo OIIIIIIALMOSCOIE. 95 considered when usinL; the ophthahiioscope in the directmethod : one is the direction which the rays of hght takeas they leave the eye under examination, and the other isfor the observer to keep his own eye emmetropic ; in otherwords, the observer wearing his correcting glasses shouldnot accommodate. Figure 82 shows that rays of light passing out of an eyedivergently must be made parallel, so as to focus upon thesurgeons own retina (emmetropic), and to do this it is
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Keywords: ., bookcentury1900, bookdecade1900, bookidref, booksubjecteyeglasses
