The simplest form of spectacle lens is the single vision lens. This is made to a single prescription to correct your vision for either long distance, intermediate distance or short distance. The thickness and weight of your lenses depend on the amount of prescription they are required to correct. (See thinner lenses option below).
Bifocal lenses contain two optical corrections with a distinct line between the two parts. The upper part of the lens contains the prescription to correct distance vision and the lower part contains the prescription for near vision. Trifocals are also available that incorporate a middle section for intermediate vision, but nowadays varifocal lenses are much more likely to be prescribed.
Varifocal lenses are used to correct multiple distances – much like the bifocal but without the distinct dividing line. Instead they have a graduated section in which the power of the lens progresses smoothly from one prescription to another, allowing the wearer to see clearly at all distances.
High index lenses (thinner lenses)
If you have a high prescription you may find that your lenses are quite thick and therefore quite heavy to wear. High index materials make lenses thinner and lighter and more comfortable to wear.
Spectacle lenses can be provided with anti-reflection coatings which virtually eliminate distracting reflections off the lens surfaces. Reducing reflected light is particularly helpful for computer users and for night driving.
Scratch-resistant / hard coating
Plastic lenses are lighter than traditional glass lenses but they scratch more easily. Scratched lenses can be irritating for the wearer and look unsightly. Scratch-resistant coatings are available to protect against damage and prolong lens life.
Photochromic lenses are lenses that change their colour according to light conditions. When exposed to sunlight they darken quickly to eliminate glare and to protect the eyes against UV. These lenses are generally nearly clear when it is dark. Many people wear these lenses and find them convenient, as they automatically darken in the sunshine and can avoid the need for you to carry prescription sunglasses. Modern photochromic materials react and fade quickly, suit most prescriptions and are more likely to be lightweight plastic than glass.
Prescription sunglasses, Sports glasses and Swimming goggles available