Lens Optical Profile
Although corrective lenses can be produced in many different profiles, the most common is ophthalmic or convex-concave. In an ophthalmic lens, both the front and back surface have a positive radius, resulting in a positive / convergent front surface and a negative / divergent back surface. The difference in curvature between the front and rear surface leads to the corrective power of the lens. In hyperopia and presbyopia a convergent lens is needed, therefore the convergent front surface overpowers the divergent back surface. For myopia the opposite is true: the divergent back surface is greater in magnitude than the convergent front surface.
The base curve (usually determined from the profile of the front surface of an ophthalmic lens) can be changed to result in the best optic and cosmetic characteristics across the entire surface of the lens. Optometrists may choose to specify a particular base curve when prescribing a corrective lens for either of these reasons. A multitude of mathematical formulas and professional clinical experience has allowed optometrists and lens designers to determine standard base curves that are ideal for most people.
A much more detailed web-published document with technical images and diagrams may be found here:
- Bifocals, Trifocals, and Progressive-Addition Lenses by H. Jay Wisnicki, M.D., Focal Points: Clinical Modules for Ophthalmologists, by the American Academy of Ophthalmologists, Volume 17, Number 6, June 1999 (Section 3 of 3)
Read more about this topic: Corrective Lens
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