This is a study to determine the effect of re-edging previously edged crown glass opthalmic lenses, which had been tempered either by a chemical process or the heat treating method. The number of lenses used in this study was ninty-six clear, single vision, spherical lenses, which varied in power from +1.00 diopters to -3.00 diopters in one-half diopter increments excluding plano powered lenses. The center thickness varied from 1.9 mm to 2.7 mm. The standard drop ball test was utilized in order to determine the effects of re-edging a "tempered" spectacle lens.
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