Eyeglass Lens Materials - Features and Benefits
Glass lenses. When Dr Hyde began practice 40 years ago, all eyeglass lenses were made of glass. Glass was heavy and could break or chip easily and caused many eye injuries potentially causing serious harm to the eye or even loss of an eye. Glass lenses are very expensive. For these reasons, glass lenses are no longer used for eyeglasses except on a special circumstance.
Because of its light weight (about half the weight of glass), low cost and excellent optical qualities, plastic remains a popular material for eyeglass lenses even today.
Polycarbonate is lighter and significantly more impact-resistant than plastic, making it a preferred material for children's eyewear, safety glasses and sports eyewear.
A newer lightweight eyeglass lens material with similar impact-resistant properties as polycarbonate is called.
High-index plastic lenses
These lenses are thinner and lighter than plastic lenses because they have a higher refractive index. The higher the ‘refractive index” faster the light travels and the thinner the eyeglass lens is. There 7 different categories of refractive index.
Aberration or Distortion Quality Number
The Aberration (Abe) number is a measure of aberration in the eyeglass lens. This quality number tells how the lens disperses different wavelengths of light as light passes through it. Lens materials with a low Abbe value have high light dispersion, which can cause noticeable distortion and chromatic aberration — an optical error visible as colored halos around objects, especially lights. It makes night vision terrible to drive. On cheaper lenses aberration is easily noticeable when looking through the periphery of eyeglass lenses.
- Aspheric lenses deals with the lens curvature changes gradually from the center of the lens to its edge.
- Aspheric lenses cause less unwanted magnification of the wearer's eyes, for a better appearance.
- Aspheric designs also improve the clarity of the wearer's peripheral vision.
- An aspheric design is an option that increases the cost of the lenses.
Lens Thickness – Center and Edge
The size and shape of your eyeglass frames will affect the thickness of your lenses, especially if you have a strong prescription. Choosing a smaller, well-centered frame can significantly reduce the thickness and weight of your lenses, regardless of the lens material you choose.
Generally, the thinnest lenses for your prescription will be aspheric lenses made of a high-index material, worn in a small frame.
Eyeglass Lens Treatments
For the most comfortable, durable and best-looking glasses, the following lens treatments are essential.
100 % UV Protection
Cumulative exposure to the sun's harmful ultraviolet (UV) radiation over a person's lifetime has been associated with age-related eye problems including cataracts and macular degeneration.
For this reason, You should protect your eyes from the sun's harmful ultraviolet (UV) radiation beginning in early childhood.
The fact that all eyeglass lens will scratch is obvious. All plastic and high-index plastic lenses require anti-scratch coating for adequate lens durability. This doesn’t mean “Scratch Proof” but Scratch resistant.” Today's modern anti-scratch coatings make your eyeglass lenses very durable and scratch-resistant. But if you're hard on your glasses or you're buying eyeglasses for your kids, ask about lenses that include a warranty against scratches for a specific period of time.
An anti- Glare or anti-reflective coating makes all eyeglass lenses better. Anti-Glare eliminate reflections in lenses that reduce contrast and clarity, especially at night. They also make your lenses nearly invisible, so you can make better eye contact and you and others aren't distracted by reflections in your lenses. Anti-Glare lenses are also much less likely to have glare spots in photographs.
Transitions Tinted Lenses
This lens option enables eyeglass lenses to darken automatically in response to the sun's UV and then quickly return to clear when indoors. If you are not buying a pair of prescription eyeglasses, this is a must with all the scientific data we now have on how harmful UV is to the eye.