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Article
January 1932

MODERN DEVELOPMENTS IN SPECTACLES

Author Affiliations

CHICAGO
From the Department of Ophthalmology, Northwestern University Medical School.

Arch Ophthalmol. 1932;7(1):113-119. doi:10.1001/archopht.1932.00820080125009
Abstract

In recent years, so numerous have been the varieties of lenses produced by zealous manufacturers that a sporadic survey of the subject is necessary to evaluate properly the progress made. Cowan1 and Jackson2 have repeatedly inveighed against "copyright glasses" and insist that the physician should have a precise knowledge of the glass he prescribes.

IMPROVEMENTS IN LENS FORM

As long as very small lenses were in vogue, the flat lenses then used were fairly satisfactory. But in large flat lenses a noticeable marginal blur occurs, owing to the astigmatism of oblique eccentric rays. This has been almost entirely eliminated within a solid angle of 60 degrees by making the lens of proper shape. "If the lens contains a cylinder, only one principal meridian can be corrected—usually the horizontal. Moreover, a lens corrected for infinity is not quite correct for reading distance" (Cowan).

Cowan suggested that convex lenses

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