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A. S. PERCIVAL, M.A., M.B. (Camb.)

Arch Ophthal. 1934;11(3):490-491.

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

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 . . . [Full Text PDF of this Article]

Author Affiliations
SHENLEY, WOKING, ENGLAND

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