The aim of this review is to indicate in a simple manner how the power of an ophthalmic lens varies with its contour, thickness and distance from the eye.
The reader perhaps will recall from his knowledge of the properties of lenses in air that, among other things, a lens possesses two principal planes (A1H1 and A2H2 in the biconvex lens depicted schematically in figure 1), which are perpendicular to the axis and so disposed that incident rays which are directed toward any point (such as A1 in figure 1) in one principal plane will be directed on emergence as though they came from a point (A2) in the second plane which is on the same side of, and at the same distance from, the principal axis as the first point. The points where the principal planes meet the principal
EGGERS H. POWER OF OPHTHALMIC LENSES. Arch Ophthalmol. 1934;12(5):753–764. doi:10.1001/archopht.1934.00830180129011
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