Lens Designs
Basic Designs
Many different lens shapes can achieve maximum optical correction for your eyes. Here are a few basic designs that deserve discussion:-
Single Vision: This type of lens is designed to adjust the focus of the eye in only one specific way. The design does not vary across the diameter of the lens. It is not adjustable or adaptable for different focus points if the eye looks through a different part of the lens.
Single Vision
Bifocal: This type of lens has two adjustments for the focus of the eye. Usually the upper part of the lens is designed to focus for far away viewing and the lower part of the lens is for viewing much closer.
Bifocal
Trifocal: This type of lens has three adjustments for the focus of the eye. The upper portion is usually designed for far viewing, the middle portion is designed for viewing at approximately arm's reach and the lower portion is designed for even closer viewing.
Trifocal
Multifocal or Progressive: This type of lens has a a variable focus. The upper portion of the lens is usually designed to improve far viewing, and the lower portion focuses increasingly closer as the eye looks more through the bottom of the lens. There are no obvious divisions or lines within the lens, so it looks just like a single vision lens, but performs like a trifocal, but with even more adjustments of focus than any trifocal.
Progressive