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To overcome some of the disadvantages presented by the use of the Beebe loupe and its modification during an operation, especially when the operator is presbyopic or desires a comfortable working focus of 15 to 20 cm., the following bifocal lens was designed.
The essential advantage of this lens is that a working area is afforded in the upper field as well as in the lower, and at the same time free lateral vision is permitted. To accomplish this a segment 10 by 24 mm. is placed almost vertically near the middle of an ordinary spectacle lens and equidistant from the top and the bottom of the lens. The upper pole of each segment is tilted templeward 1 mm. to allow for separation of the visual axes in the upper fields. The segments are
Richards GM. SPECTACLE LENSES FOR USE DURING OPERATIONS. Arch Ophthalmol. 1940;23(3):625–626. doi:10.1001/archopht.1940.00860130691020
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