Multifocal Designs
Cataract Lenses

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There are certain distortions or aberrations inherent in any lens with power. The higher the power, the more pronounced these aberrations become. An aphakic spectacle lens (one which is used in post-cataract surgery) can contain as much as eight to twenty or more diopters of plus power, making peripheral distortions a significant problem by reducing the useful area of the lens. One way of minimizing these distortions is through the use of aspheric front surfaces. An aspheric surface is one in which the shape is not spherical, but rather emulates the shape of the human cornea which is steeper in the center and gradually gets flatter as it radiates toward the periphery as illustrated above. A lenticular design is often used in high plus prescriptions for the purpose of minimizing lens thickness. It consists of a carrier lens and a bowl. The bowl is the portion containing the prescription. A lenticular lens may be either aspheric or spherical in shape.

Today, post cataract spectacle lenses are being used less frequently than they once were. This is due to improvements in aphakic contact lenses and intraocular lens implants, both of which are optically superior to high powered spectacle lenses.