. On the anomalies of accommodation and refraction of the eye, witha preliminary essay on physiological dioptrics. to the conclusion, that with this degree3f hypermetropia, eyes cannot long consecutively accommodate them-selves to the point of intersection of their visual lines. With stillhigher degrees of hypermetropia, as shall hereafter appear, binocular, 122 RANGE OF ACCOMMODATION. and with the highest degree (absolute hypermetropia) even monocularvision is never acute. The foregoing applied to the position of the range of accommoda-tion, with reference to the convergence of the visual lin
. On the anomalies of accommodation and refraction of the eye, witha preliminary essay on physiological dioptrics. to the conclusion, that with this degree3f hypermetropia, eyes cannot long consecutively accommodate them-selves to the point of intersection of their visual lines. With stillhigher degrees of hypermetropia, as shall hereafter appear, binocular, 122 RANGE OF ACCOMMODATION. and with the highest degree (absolute hypermetropia) even monocularvision is never acute. The foregoing applied to the position of the range of accommoda-tion, with reference to the convergence of the visual lines.—We mustnow take the form of the curves into closer consideration. Even inFig. 60, we see that the curves of M are concave upwards, whilethose of H are convex upwards. If with this we compare Fig. 57,it appears, that the curves for the emmetropic eye keep the mean be-tween M and H. The reason of this lies in the fact that, withslight convergence, a myopic eye can accommodate proportionallyless; a hypermetropic, on the contrary, more (but also must soaccommodate) than the emmetropic. The diagram Fig. Gl,. 11°21 22o50 34°32 46°38 59°20 72°50 will make this plain. It contains the curves of the nearest andfarthest points, as function of the convergence, both for the em-metropic eye E (the middle ordinary lines), and for the myopic M(the dotted lines), and for the hypermetropic, H (the striped and dotted1 . , . „ .,.. ,1 lines); -j- is, in order to facilitate comparison, assumed = 4 and IMPORTANCE OF THE DIFFERENCE. 123 the maximum of convergence is taken at 59° 20. The letters E,M, and H are placed before the farthest points, as defining the re-fraction ; Hm (manifest hypermetropia) stands before r the manifestfarthest point, H< (total hypermetropia), before rtt\\& absolute farthestpoint. In other respects, the letters have the same signification asin Pig. 60. Now the study of this diagram shows :— 1. That with parallel visual lines, the emmetropic eye can bring i
Size: 1444px × 1730px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1860, bookidonanomalieso, bookyear1864
