Glasses: Types and uses
Most people will probably need a pair of glasses to improve their vision at some stage in their life.
The NHS recommends having an eye test at least every 2 years.
Although some people may qualify for free eye tests on the NHS, glasses themselves have to be paid for.
Some people may need to wear glasses all the time. Others may need them for specific reasons, like driving, reading or computer use.
Some people may need more than one pair, for close-up work and things further away, or they may consider bifocals or varifocals.
Prescription glasses can also be tinted so they double up as sunglasses, or have a special coating so they become darker in brighter lighting.
What types of lenses are available?
As technology advances so, too, do lenses. In the past, lenses were made exclusively of glass. Today, most glasses are made of high-tech plastics. These new lenses are lighter, do not break as easily as glass lenses, and can be treated with a filter to shield your eyes from damaging ultraviolet light.
The following modern lenses are lighter, thinner and more scratch-resistant than glass lenses or the older, common plastic lenses.
- Polycarbonate lenses. These lenses are impact-resistant and are a good choice for people who regularly participate in sporting activities, work in a job environment in which their glasses may be easily scratched or broken, and for children who may easily drop or scratch their glasses. Polycarbonate lenses also provide ultraviolet protection.
- Trivex lenses. Made from a newer plastic with similar characteristics of polycarbonate lenses. It is lightweight, thin and impact-resistant and may result in better vision correction in some people than polycarbonate lenses.
- High-index plastic lenses. Designed for people who require strong prescriptions, these lenses are lighter and thinner than the standard thick lenses that may otherwise be needed.
- Aspheric lenses. These lenses are unlike typical lenses, which are spherical in shape. Aspheric lenses are made up of differing degrees of curvature over its surface, which allows the lens to be thinner and flatter than other lenses. This also creates a lens with a much larger usable portion than the standard lens.
- Photochromic lenses. Made from either glass or plastic, these glasses change from clear to tinted when exposed to sunlight. This eliminates the need for prescription sunglasses. These lenses may not darken in a car because the windscreen could block the ultraviolet rays from the sun.
- Polarised sunglasses. Light reflected from water or a flat surface can cause unwanted glare. Polarised lenses reduce glare and are useful for sport and driving. These lenses may cause the liquid crystal displays on the dashboard of cars to appear invisible.
The type of vision problem that you have determines the shape of the lens. For example, a lens that is concave, or curves inward, is used to correct short-sightedness, while a lens that is convex, or curves outward, is used to correct long-sightedness. To correct astigmatism, which is caused by distortions in the shape of the cornea, a cylinder shaped lens is frequently used. Simply put, the lens is a tool you use to focus light appropriately onto your retina.