SPECTACLE LENSES
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Lens Types |
| The types of spectacle lenses can be mostly thought of terms of single vision, bifocal and varifocal lenses.
Single vision are mostly used for general use of for simple reading spectacles. |
| However, for most people who need reading spectacles, the lenses that give good reading vision will blur things in
the distance. You are therefore faced with continually putting your spectacles on and off. The times that you do this tends to increase
as you get older. Bifocals and Varifocals get around this by giving good distance vision through the top of the lens, and reading through
the lower part of the lens. Therefore avoiding the constant on and off bit! Bifocals have a line dividing the upper and lower parts of
the lens, Varifocals merge from one part to the other. |
| Bifocals and Varifocals are available in a number of different designs and to some degree, qualities. Varifocals,
in particular, have gone through a lot of development changes over the last few years. The newer designs generally having wider and smoother
vision areas within the lens. The newer generations of Varifocals unfortunately also being more expensive. This is often why there can seem
to be a wide range of prices for Varifocals. Due to the better optics, improved adaption and being generally available in a wider range of
materials, we tend to recommend using the newer lenses where possible. |
| Which type of lens is best for you, depends on many factors and is impossible to advise via a website. The best
way is to discuss things with the Optometrist or Dispensing Optician following your next eye examination. |
Lens Materials |
| We now have a vast array of meterials to choose from for spectacles, each with particular benefits for the wearers.
Ordinary plastic lenses are still probably the most commonly used. Thay are fairly light, safe and cheap with good optical properties.
However they can become quiet thick and heavy in higher prescriptions. Higher index materials allow the lenses to be made lighter and
thinner than ordinary plastic. They do become more expensive as the index increases and they benefit more from anti-reflection coatings (see later).
Polycarbonate lenses are particularly good for the modern rimless designs due to the material being very resistant to breakage. |
| We have had glass photochromic for many years, the well known trade name being Reactolites. They were (and still are) very good, but being glass are
also heavy and breakable. For the last few years we have also had plastic photochromic materials. These have all the benefits ie they go darker when in sunlight
but are also lighter and safer. They are also now available in many different colours and high index materials to make them thinner as well. |
| Ordinary glass is now rarely used, however there is little doubt that if you want thin lenses then high index glass will give you the thinnest
lens. Currently glass can be made much thinner than plastic. |
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Other Items |
| Anti-reflection coatings, are a coating applied to a lens to reduce the reflections from the front and back of the lens. The benefit
being found particularly for night driving, office working and generaly improved optics of the lenses. For example you would never find a good camera or
binocular lenses without these coatings. They are particularly helpful on higher index lenses where the reflectivity of the material is greater.
With the new Crizal Alize coating, keeping the lens clean and clear is now even easier. |
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Last modified: Jan 2005
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