A large variety of lens materials exist such as:
1) Allyl resin plastic lens
2) Aspheric lens
3) CR-39 plastic lens
4) Glass lens
5) High-index plastic or glass lens
6) Polycarbonate plastic lens

1) Allyl resin plastic lens:
These are the lightest of all lenses. However they are thicker than other plastic lenses, are less scratch-resistant, and do not block as much ultraviolet light as polycarbonate and glass lenses.

2) Aspheric lens:
These also aid in cutting down on thickness and weight, especially when combined with high-index materials. These have curves that are nonspherical and change gradually from the center to the outside of the lens. They are available in single-vision, bifocal, and progressive-addition designs.

3) CR-39 plastic lens:
These are durable and have a higher scratch resistance then polycarbonate. They are also unlikely to fog.

They are able to have scratch resistant coating applied to the lens along with an ultraviolet coating and anti-reflective coating, therefore will provide better ultraviolet protection to the user. They also present more choice when it comes to tints and coatings.

4) Glass lens:
Is scratch-resistant, comes in many colors, absorbs ultraviolet light, and causes the least amount of distortion. However are heavier than newer polycarbonate plastics and are breakable, so that they must be treated with heat or chemicals for sports or other endeavors that are breakage-prone.

5) High-index plastic or glass lens:
These offer the best ultraviolet resistance and are also thin and light. However they are the most expensive of all lenses, are easily scratched, and can shatter on impact.
These are made of either glass or plastic that is compressed, giving them a high index of refraction (IOR). These lenses bend light more than other lenses, so a person who requires a great deal of correction does not have to wear extremely thick lenses.

6) Polycarbonate plastics lens:
Is light in weight, blocks UV rays, is shatter resistant and is used in sports glasses and glasses for children and teenagers. It’s soft and would scratch easily therefore a scratch resistant coating is typically applied after shaping and polishing the lens.

What’s the purpose of lens coatings?
Lenses of any material can be treated with coatings to give the lenses desired properties such as:

1) Anti-reflective coatings (A-R coatings)
Are metallic oxide coatings that are vacuum-applied to the lens surface to reduce reflections from the front lens surface and eliminate reflections from the back. This reduced amount of reflection enhances the appearance of the glasses and also allows more light to pass through the lenses, which can improve vision in low-light situations like night driving. Anti-reflective coatings also provide some protection from scratching.

2) Mirror-coated lenses
Are coated with a layer of reflective material that greatly reduces the amount of heat entering the eyes. However, these lenses reduce visual acuity and are somewhat like looking through a two-way mirror. This kind of coating is purely cosmetic. They come in a number of colours and are highly reflective.

3) Scratch-resistant coatings (also known as “hard coat”)
Are applied to the front and back surfaces of glass and plastic lenses to protect against accidental scratching and to improve durability. Some high-quality lenses come from the factory with scratch coatings already applied. No coating can make lenses completely scratch proof.

4) Ultraviolet -resistant coatings protect the eyes from ultraviolet sun rays that have been shown to cause cataracts and certain diseases of the eye.

If you spend a lot of time outdoors, have your lenses anti-UV coated.
The best eye protection from UV radiation is a good pair of sunglasses that is rated to block 99 percent to 100 percent of the full UV spectrum.
The lenses should filter wavelengths up to 400 nanometers to cut out all harmful rays. UV coating can be applied to all glass and plastic lenses, except polycarbonate, which doesn’t need coating because it absorbs virtually all UV rays.

What’s the purpose of lens tints?

Tinted lenses have the following purposes:
- Increase comfort in bright light situations
- Reduce the glare from computer screens or fluorescent light
- Make a fashion statement

What solid colour tints are there? And what is the purpose of each?
There are many colours such as:
1) Amber, yellow or orange
2) Blue or purple
3) Brown & Copper
4) Gray, Smoke or Green
5) Near Black
6) Rose or Vermilion

1) Amber, Yellow or Orange lens:
These lenses allow some light to pass through the lens making them a better choice for overcast skies, but hard to recommend for use in bright sunny days – yellow and orange. Yellow lenses afford excellent visibility in nighttime applications.
Amber tints are a good choice for working outside as both harmful UV rays and glare caused by the suns rays are blocked out with these lenses. Like grey lenses, amber colored lenses assist user in seeing finer details.

2) Blue or Purple lens:
Great all purpose lenses. Their mellow light tint is wonderful and soothing. Also, they afford good protection in sunny days (although not like a dark lens) yet will also carry over into darker conditions. Blue tints also reduce glare produced by halogen or fluorescent lights.

3) Brown & Copper lens:
These lenses increase contrast between colours and are the preferred tint for driving. This contrast also cuts glare and sharpens imagery.

4) Gray, Smoke or Green lens:
These lenses are the most popular because while they cut bright light they also help to keep colours looking natural.

5) Near Black lens:
Great protection for very light sensitive eyes and super sunny summer days.

6) Rose or Vermilion lens:
These popular lenses provide enhanced contrast and definition in high glare situations such as seen in water and snow sports.
Rose lenses are also recommended for indoor office use for those working with computers who are at risk of eye strain and headaches. While stylish they are also calming for the eyes.

What is a gradient tint?

Gradient tint is the term used to describe a lens with a fully tinted upper portion that gradually diminishes towards the bottom of the lens.

Ultimately, the bottom section of a gradient lens will be completely clear. The purpose of this type of tinting is that the upper portion of lens will reduce glare and UV exposure while the bottom portion simultaneously offers the wearer the convenience of a clear area for reading and/or viewing objects up close.

What are specialist lenses?
There are various types of specialist lenses such as:
1) Photochromic lens
2) Polarized lens

1) Photochromic/ transition lenses
These are lenses which darken each time they are exposed to ultraviolet light and radiation.

These lenses change from clear lenses to tinted whenever the user walks into a sunlit area. They protect the wearer’s eyes from 99.9% of the harmful UV rays and help achieve clearer vision in areas with bright glare from the sun. Once the wearer is back inside or no longer exposed to UV rays, the lenses will transition back to clear/transparent lenses.

The rate of darkening depends on the ambient temperature. These lenses do not become as dark when driving because the car’s windshield absorbs some of the ultraviolet light that causes the lenses to darken. These lenses are available in plastic as well as glass and they may be either brown or gray in color. Such lenses can be used in prescription or non-prescription eyewear and are ideal for individuals with sensitivity to light.

2) Polarized lenses
They are very useful in protecting eyes from UV rays and reducing eye strain from reflections when skiing, participating in water sports, working on flat roads or snow covered areas which are all highly reflective resulting in an increase in bothersome horizontal light waves.
Polarized lenses only allow the vertical light waves to pass through the lens therefore reducing problems due to glare.
They are available in plastic, glass, and high-index materials, but they are relatively expensive compared to other lenses.

What types of corrective lenses are available?

Lenses are usually classified into one of 3 categories:
1) Single vision
2) Bifocals
3) Multifocals

1) Single vision lens:
Have the same focal power throughout (top to bottom) and can be used to correct nearsightedness, farsightedness, astigmatism or a combination of these disorders. Most people who wear glasses before the age of 40 have single vision lenses.

2) Bifocal lens:
Have two parts: the upper part normally used for distance vision and the lower part used for near-vision tasks such as reading. Many people after reaching age 45 develop a condition called presbyopia, which is a deterioration in the ability of the eye’s natural lens to expand or contract in order to focus on close objects. People with presbyopia need a special lens for reading and may need a different lens for seeing in the distance.

Until recently, bifocal eyeglasses had a line going across the entire length of the lens. Now there are a number of variations on the theme. All work the same way, by reserving part of the lens for near-vision correction. The rest of the lens can be used for distance vision correction or can have no correction at all.

3) Multifocal lens:
Has more than one focus. In addition to bifocal lenses the other multifocal is a progressive addition (no-line bifocal) lens that increases in power from top to bottom. Progressive lenses have no clear dividing lines as the focus changes from bottom to top. They have become popular in recent years because they look like single vision glasses.