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Spectacles Parts & Glasses Glossary Part #2

VISION LENS TYPES in Glasses, Reading Glasses, Spectacles

Lenses Can Be Fun (?)

Lenses Can Be Fun - Especially Paul Smith

Those of you who have had a prescription will surely be familiar with your own prescription and the lenses you have had.  Of course each time you have a new eye test this may change – particularly with age.  But wherever you buy your new glasses~spectacles they will have one of the following types of lenses.  If you missed part #1 of the Spectacles Blog glossary – please see the earlier post about the lens materials.

With thanks to The College of Optometrists for the bulk of the source of the below.

Single-vision lenses The most simple spectacle lens made to a “single prescription” to correct a particular  problem. Concave lenses correct short sight and convex lenses correct long sight. Concave lenses are generally thinner in the centre than they are at the edge and convex lenses are usually thinner at the edge than at the centre. How curved the lens is and how thick it is depends on the degree of long or short sightedness.
Bifocals Bifocal lenses correct two different optical needs with a distinct horizontal dividing line between the two prescriptions. Most bifocals are for presbyopia and which demands a different prescription for short vision. The top of the lens corrects long distance vision and the bottom is for near vision.
“Trifocals” You can get these which have three sections with a central correction for middle vision.
Varifocal or progressive lenses Varifocal lenses(or “progressive lenses”) are also used for correcting presbyopia but have no visible dividing lines between the different corrections and no sudden change but a graduated change from one prescription to the other, for clarity with all distances. Some say that these lenses look better as they don’t draw attention to the “bi/tri-focal ature associated with age.
(High-index and aspheric lenses: If the need is extra high-powered lenses high-index materials & aspheric designs mean that lenses can now be made thinner, lighter and better looking than previous lens types. High-index materials make short sight lenses thinner, while aspheric designs minimising the amount of material, make lenses for long sight both thinner and lighter).
Prescription sunglasses It is important to protect eyes from an excess of ultraviolet (UV) radiation. Similarly, eyes need protection from reflected light (sand/snow –  or just long sunny periods outside). Sunglasses can be made with single-vision, bifocal or varifocal lenses (in any design) for UV protection.  (Both of Spectacles Blog’s recommended on-line retailers offer prescription sunglasses.)

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