Sight-testing made easy / by W. Wright Hardwicke.

  • Hardwicke, W. Wright (William Wright), 1848-
Date:
1920
Catalogue details

Licence: Public Domain Mark

Credit: Sight-testing made easy / by W. Wright Hardwicke. Source: Wellcome Collection.

    72/104 (page 56)
    lilies in that Mn., with convex sphericals. The strongest with which the lines can be counted denotes the amount of liypermetropia^ say + 2*0. (5) Then test the myopic Mn., the vertical, by placing lines in that Mn., with concave sphericals. The weakest with which the lines can be counted denotes the amount of myopia^ say — 1*0. Total re>ailt: Hypermetropia of + 2*0 in the horizontal Mn. and myopia of — 1*0 in the vertical Mn. The sum of the two denotes the amount o f ((Migniatisin, and the strength of the cylindrical lens required. Ckmrection : Cyl. -f 2*0, ax. h., o cyl. — 1*0, ax. V., which reduced to a spheric and a cylinder, give the following: Formula : Sph. + 2*0 3 cyl. *k^3*0, ax. v. Tdie sph. 4 2*0 corrects the hypermetropia in the horizontal Mn., but makes the myopiia in the vertical Mn. more myopic, by — 2*0, than before, which is corrected bv — 3*0. Alternatire forinuJa : Sph. -- 1*0 3 cyl. + 3*0 ax. h. Here the sph. — 1*0 corrects the myopia in the vertical Mn., but makes the hypermetropia in the horizontal Mm more hypermetropic by — hO, necessitating -f 0)0 instead of H- 2*0 D. to correct it.