Lens Form & Analysis
Corrected Curve Lenses

Some Possible Shapes of a +1.00 Sphere

By applying the formula F1 + F2 = FT, it becomes evident that any given powered lens may take on a virtually infinite number of shapes and still produce the desired power. The illustration above shows just a few examples of what shapes a simple +1.00 spherical lens could possibly assume.

 

There are certain aberrations or distortions inherent in any lens with power. Most spectacle lenses made today are shaped so that these aberrations are minimized. These are known as corrected curve lenses. Corrected curve lenses are designed so that the back surface, also called the ocular surface, is as close to – 6.00 D as can be reasonably expected given the power called for. As lenses increase in plus power, the ocular surface generally gets flatter, while stronger minus lenses are shaped with steeper back curves. As the eye rotates in various directions, a – 6.00 D back curve allows the distance from the eye to the back of the lens to remain relatively consistent.