Skiascopy and its practical application to the study of refraction . Fig. 26. Fig. 27. A Distance Measure.—Where the concave mirror isemployed, the distance remaining fixed throughout the test,it is only necessary that the surgeon should properly placehimself at the beginning, and retain his position. He canthen dismiss the consideration of the distance, or providefor it by the addition of 1. D. to the concave sphericallens or the subtraction of 1. D. from the convex sphericallens that brings the point of reversal to his eye. With the plane mirror no measure is necessary wherethe test is used
Skiascopy and its practical application to the study of refraction . Fig. 26. Fig. 27. A Distance Measure.—Where the concave mirror isemployed, the distance remaining fixed throughout the test,it is only necessary that the surgeon should properly placehimself at the beginning, and retain his position. He canthen dismiss the consideration of the distance, or providefor it by the addition of 1. D. to the concave sphericallens or the subtraction of 1. D. from the convex sphericallens that brings the point of reversal to his eye. With the plane mirror no measure is necessary wherethe test is used only to approximate the refraction, the sur-geon soon learning to guess at the distance closely enough to 104 GENERAL CONSIDERATIONS. be within D. of the amount of myopia present withthe lens fixed upon. But for exact measurement it is con-venient to have something to measure from the patientseye to the surgeons. This may be either a tape attachedto the trial frame or lens disk (Burnett), and picked up andheld to the surgeons eye when the test is completed
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectretinos, bookyear1896
