Non-conventional Types of Varifocal Spectacle Lens

Abstract

The condition known as presbyopia is a normal physiological process, which begins to cause problems with near vision in middle-age. Unfortunately, although there are many varifocal lenses available which give some form of continuously variable vision, as in the pre-presbyopic eye, all current designs are compromise approaches to the problem, Sullivan and Fowler (1989) reporting a 12.5 % failure rate with one type. The aim therefore of this project was to investigate three different approaches to the one normally used, these being liquid crystal lenses, gradient index optics, and deformable lenses. In the case of liquid crystals, an extensive literature survey was carried out, and a theoretical analysis of performance. In the case of gradient index optics and deformable lenses, a literature review was made and practical measurements were carried out, on experimental lenses constructed in the laboratory. The liquid crystal lenses would seem to offer the best prospects for the long term, although there are severe difficulties to be overcome before they can be mass- produced. Gradient index lenses still require the development of a suitably stable lens material, and even then would not seem to offer many advantages over the existing lenses. Deformable lenses can be readily constructed, but are difficult to mass- produce, and suffer from leakage of the hydraulic control system