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A CRITIQUE

BENJAMIN FRIEDMAN, M.D.

Arch Ophthal. 1940;24(3):490-499.

	Since this article does not have an abstract, we have provided the first 150 words of the full text PDF and any section headings.

The Jackson crossed cylinder is an outgrowth of an exceedingly clever device called the Stokes lens, which was introduced in 1849.¹ It will be recalled that the first attempt at correcting astigmatism by means of a cylindric lens was made by the astronomer Airy² in 1827, only twenty-two years previously. Airy's pioneering step had attracted little of the attention it merited. Cases of astigmatism were still reported as rarities, and cylindric lenses were obtainable from only a few opticians on special order. The pristine trial cases of the day contained few, if any, cylinders and the Stokes lens was invented to fulfil this need. It consisted of two cylinders, one planoconvex and the other planoconcave, placed with the flat surfaces in apposition and so held in a housing that they were capable of being rotated simultaneously in opposite directions. When the axes of the two cylinders were parallel . . . [Full Text PDF of this Article]

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