Spectacle lenses have been available now for several hundred years, and initially only the very rich would have been able to afford them. Thankfully, times have changed and there is now a vast range of lenses available to suit all budgets.
Originally the only material for a lens would have been glass. Indeed, it is only during the past two decades or so that other materials have become widely available. Glass lenses have the advantage of being relatively hard wearing and durable unless dropped, in which case glass lenses are likely to suffer the same fate as any other glass item. For most prescriptions glass is now considered to be too heavy and relatively unsafe. It mainly has a specialist use for high prescriptions, where reducing lens thickness is imperative.
Organic materials include ordinary spectacle plastics such as CR39, resins and polycarbonate. They are significantly lighter in weight than glass lenses and considerably more impact resistant. Also, with modern surface treatments, they can be just as resistant to surface abrasion as glass lenses.
Both glass and organic materials are made in several different refractive indices. The refractive index is a measure of the material's ability to bend or refract light waves. The higher the index the less material is needed to bend the light beam by a fixed amount. Thus the choice of refractive index becomes a valuable tool in producing lenses which are as thin, light and as comfortable to wear as possible.
Types of Spectacle Lens
These lenses have just one focal range which is prescribed to suit individual requirements whether for distance, intermediate or close viewing.
As part of the natural ageing process, we gradually lose the ability to focus clearly on objects which are close enough to hold. The condition is known as presbyopia and it begins to affect most people in early middle-age. People with good long distance vision will now begin to need spectacles for reading. Those who are already wearing spectacles to improve their distance vision will require an extra pair of spectacles optimised for reading. Alternatively, bifocal lenses can be worn in which the upper and lower sections are split to enable comfortable distance and near focussing in one pair of spectacles.
Varifocals perform much the same functions as bifocals. They have the advantage of an improvement in the mid-range focussing as there is now a gradual change of strength down the lens. They are also more attractive in appearance as there is no line or curve visible where the distance and reading sections divide.
There are many different designs of varifocal available, some of which may suit your prescription or daily needs better than others. Varifocal lens design can be optimised for general use, sports, and increasingly for computer and workstation use. Our dispensing staff will be pleased to guide you through the process of choosing your ideal lens.