. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, clo-plegic has been instilled. ASTIGMATISM. 139 6. The writers pointed line test, as shown in figure 109,is a series of one-minute black squares, in tliree parallellines at right angles to each other, on a cream-colored card ;the squares and adjoining spaces making a five-minuteangle for six meters. By means of a clockwork and bat-tery, this dial may be revolved by pressing a button. Theprinciple of the test is the same as the perforated Fig. 109. 7. The Perforat
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, clo-plegic has been instilled. ASTIGMATISM. 139 6. The writers pointed line test, as shown in figure 109,is a series of one-minute black squares, in tliree parallellines at right angles to each other, on a cream-colored card ;the squares and adjoining spaces making a five-minuteangle for six meters. By means of a clockwork and bat-tery, this dial may be revolved by pressing a button. Theprinciple of the test is the same as the perforated Fig. 109. 7. The Perforated Disc (Fig. 110).—This is a modifica-tion of the astigmatic chart. A piece of white cardboardor metal, about ten inches square, has small, round perfora-tions made in it of certain definite size. Each perforation isseparated from its neighbor by the distance of its openings are arranged in series of one, two, or threeparallel lines, exactly as in the pointed line test. Thischart or disc is hung on the window-pane, or an illumina-tion is placed behind it. The patient, looking at the disc, 140 REFRACTION AND HOW TO REFRACT. signifies which scries of perforations appear to coalesce andform hnes. This test is not commonly known or used. It
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