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April 22, 1899

New Instruments.

JAMA. 1899;XXXII(16):899-900. doi:10.1001/jama.1899.02450430053026

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A Pointed Line=Test for Astigmatism.  BY JAMES THORNTON, M.D.ADJ.-PROFESSOR OF THE EYE IN THE PHILADELPHIA POLYCLINIC AND COLLEGE FOR GRADUATES IN MEDICINE. PHILADELPHIA, PA.Having been unsuccessful in finding an astigmatic dial that was mathematically correct in every particular, or one that fulfilled the true definition of the word "a-stigmatism," the writer herewith presents a chart which appears to meet the necessary requirements for normal visual acuity at a distance of six meters. This chart is composed of a series of squares placed in three parallel rows, at right angles to each other, each square and space representing a visual angle of one minute, so that, to the astigmatic eye, the squares will coalesce and appear as straight lines. This chart, mounted on a square card, with peripheral markings, for purposes of record, may be slowly rotated by the surgeon; or when attached to a concealed clock and small

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