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February 1941


Arch Ophthalmol. 1941;25(2):355-356. doi:10.1001/archopht.1941.00870080179017

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To the Editor:  —In a paper on the Jackson crossed cylinder (Friedman, B. : The Jackson Crossed Cylinder, Arch. Ophth.24: 490 [Sept.] 1940) the statement is made, with reference to determining the correct axis, that the simple procedure of temporarily overcorrecting the cylinder in the trial frame by 0.50 to 1.00 D. and then rotating it a few degrees to either side of the tentative axis is far less complicated and optically accomplishes exactly what the Jackson crossed cylinder does. This statement is not quite accurate; the mode of action of the several tests is different, as the following analysis will show.The rotating cylinder method is practiced in two or three ways. One way is to rotate the cylinder from the tentative axis to the position of greatest clearness. This method may be called the blur-to-clear rotation. The end stage is the "clear" position. The other method is to

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