The two instruments that I herewith present have proved of sufficient value, in facilitating the testing of the refraction of the eye, to justify me in calling the attention of the members of the Section to them. The first is
A TRIAL-FRAME FOR SKIASCOPY.
It is simply a light trial-frame, in each cell of which is fixed a metal disc, with a central opening large enough to allow the application of the shadow-test through it.Upon the disc are enameled bands of black and white, each occupying an angle of 30 degrees of the disc. In the center of each band is marked a point, white in the black bands, and black in the white bands. This constitutes a graduation to 15 degrees spaces. The center of a white band marks 90 degrees, and the center of a black band, 180 degrees, of the usual graduation of the trial-frame. This
JACKSON E. AIDS IN THE MEASUREMENT OF REFRACTION. JAMA. 1900;XXXV(20):1270–1271. doi:https://doi.org/10.1001/jama.1900.24620460020001i
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