Archives of ophthalmology and otology . the intensity of illumination,whereas, by increasing it, a dark cloud became conspicuous in thecentre of the ophthalmoscopic field of vision. In this manner Ithought to have arrived, as to the width of the hole in the mirror, atlimits which, in the construction of ophthalmoscopes, ought not 42 H. Knapp to be transgressed in favor of some one or other peculiar arrange-ment. The diminution of the hole in the mirror, furthermore, has thedisadvantage of throwing a great quantity of light into the pa-tients eye, which dazzles him, and causes, by contraction o
Archives of ophthalmology and otology . the intensity of illumination,whereas, by increasing it, a dark cloud became conspicuous in thecentre of the ophthalmoscopic field of vision. In this manner Ithought to have arrived, as to the width of the hole in the mirror, atlimits which, in the construction of ophthalmoscopes, ought not 42 H. Knapp to be transgressed in favor of some one or other peculiar arrange-ment. The diminution of the hole in the mirror, furthermore, has thedisadvantage of throwing a great quantity of light into the pa-tients eye, which dazzles him, and causes, by contraction of the pu-pil, a limitation of the ophthalmoscopic field of vision. A greatportion of the rays returning from the eye under examination isintercepted by the zone of the mirror adjacent to the hole, andtherefore lost to the observer, which fact accounts for the dimin-ished brightness of the ophthalmoscopic image. The arrangement of the new simplified ophthalmoscope is illus-trated by the accompanying figure, which represents the instru-. FlG. I. ment in its natural size. The disk contains an empty hole andtwenty-three lenses, viz., -j- 3, 4, 5, 6, 7, 8, 10, 12, 16, 24, 48,and —2, 3, etc., as the convex lenses. The refractive intervals A Nczv Opht/iahiioscope. 43 are as follows: from 2 to 3 = | ; 3 to 4 = y^g-; 4 to 5 = ^V 5 5 to 6 =^-6io7=-i^- 7to8 = ,v; 8 to io = -j-V; 10 to i2 = ^v; ^2 to i6 = ^ ; i6 to 24 = -fV ; 24 to 48 = V The disk has a central spiral spring, held down by the cover,which is fastened by a thumb-screw and regulates the rotationof the disk. On the front surface of the disk is a point-like de-pression under each lens for the reception of the end of a spring,whenever the centre of an auxiliary lens is opposite the centre ofthe aperture in the mirror. The number of each glass can beread through an aperture in the cover when the glass is movedbehind the hole in the mirror. The concave glasses are under-lined ; the convex glasses have no distinguishing mark. The
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Keywords: ., bookcentury1800, bookde, booksubjectear, booksubjectophthalmology
