A Simple Guide to Spectacle Lenses and their Coatings Single Vision These are the simplest form of spectacle lens using either a convex or a concave lens. The convex lenses are used to correct long-sightedness (hypermetropia). A long sighted persons’ focus is actually some way behind the back of the eye and the convex lens pulls the rays of light together sooner than they normally would be. A concave lens is the opposite and is used to correct short-sightedness (myopia). A short sighted persons’ focus is focusing before the back of the eyeball. The concave lens pushes the rays of light further apart so that they arrive together in proper focus at the back of the eye.
Bifocals This lens invented over 200 years ago is seen less frequently these days and contains two optical corrections. The most common use of a bifocal is for people who have become presbyopic, as we do with age and need assistance with both close work and long distance vision. The upper part of the lens is used to correct the distance, whilst the lower half assists with reading or other close work. Between the two areas there is a distinctive line.
Varifocal The varifocal or progressive lens, were invented in the 50’s early 60’s and are a modern day equivalent to bifocal lenses. These lenses have no distracting lines between the prescription areas, but have a graduated section that moves smoothly from one prescription to the other. They provide the dual benefit of being better cosmetically without the distracting lines across the lens for the wearer.
Scratch Resistant Coating People tend not to have the time to treat their spectacles as well as they might. Beyond that there are every day accidents. Scratched lenses can at the least be an irritant to the wearer and look unsightly, and at worst become impossible to use. However, lenses can now be dispensed with a scratch resistant coating, which prolongs their life.
Transitions These are fast acting variable tinted lenses which darken in sunlight. Indoors they are clear, but outside they rapidly darken, effectively changing them into conventional sunglasses. Transitions are available in grey or brown tints and offer 100% protection against damaging UV light.
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