Image from page 86 of "Refraction and motility of the eye, with chapters on color blindness and the field of vision" (1920)
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scope before his eye and looking Fig. 43a. through a + 6 or + 7 lens, the physicianshould first throw the light into the eye froma distance of twelve or fifteen inches and gradually ap-proach his head to that of the patient. In this way he notonly has the advantage of the condensation of light fromthe concave mirror, but when he approaches to the properdistance, sees all the details magnified by a convex lens.Turning the mirror to one side so as to throw the pupil inthe shadow and then exposing it to the bright light sud-denly, he should note whether it reacts properly to the OPHTHALMOSCOPY. 69 light stimulus. The light reflected from the retina returnsto the observers eye, so that the whole pupil seemsilluminated by a brilliant glow which, if perfectly clear,indicates that the refractive media are transparent. Heshould note whether the pupil is round, or whether its edgeis adherent at any point to the lens, causing it to expandand contract unevenly, or whether any spots of pigment on
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Fig. 44. the lens near the margin indicate previous adhesions. Ifthere are spots of this kind or opacities in the cornea, lensor vitreous, they will interfere with the return of light tothe eye of the observer and will appear as black spots orma^es against the red background. Then, while watchingthese closely, the patient is directed to move his gaze up ordown, and the surgeon notes carefully their position rela-tive to the margin of the pupil and can tell quite accuratelyon which of the refractive media they are situated. Suppose, for instance, an opacity that when the patient 70 EFFRACTION AND MOTILITY OF THE EYE. looks straight ahead appears like a black point in thecentre of the pupil. When the eye turns upward, it moveswheel-fashion round a centre of rotation, and objects infront of the pupillary plane will seem to move upwardwhile those behind will have a corresponding motion down-ward. If the opacity is in the cornea, it will appear to
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