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March 1934


Author Affiliations


Arch Ophthalmol. 1934;11(3):490-491. doi:10.1001/archopht.1934.00830100112007

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Periscopic lenses are still regarded frequently as lenses which give good definition in the peripheral parts of the field. This is what is required in a photographic lens, and excellent photographic lenses have long been made; striking photographs are often given of test types placed 30 degrees from the axis of a biconvex lens, and these are contrasted with those that have been produced by a so-called periscopic lens of the same power. But this lens is not a periscopic spectacle lens ; it is only a photographic lens provided with a fixed stop. The periscopic spectacle lens has a movable stop (the iris) and should give a well defined macular image of the eccentric part of the field under examination, when the eye ranges from side to side.

The diameter of a macular cone is about 0.002 mm., and for distinct vision, therefore, the radius of the circle

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