Choosing the base curve for an ophthalmic lens.

Although optometrists can be expected to be responsible for the base curve, which determines the form of the lens they prescribe, they seldom specify the base curve to the optical laboratory. They may ask for a corrected-curve lens without specifying the kind of corrected-curve lens. If optometrists were to specify what they want in terms of a convex spherical base curve and allow the laboratory a leeway of p1.00 D, the laboratory could probably fill the order with an uncut lens from stock. With a series of semifinished lenses with convex spherical base curves spaced 2.00 D apart, the laboratory can supply a finished lens that will meet almost any need. For glasses to be used for distant objects, first consideration is usually given to minimizing the unwanted sphere and cylinder in the periphery of the lenses. For those who want to aim at this objective, I have worked out a series of convex spherical base curves that can be used for various combinations of spheres and cylinders.