David Balfour

You are going to need a quality eye glass frame. We have hundreds in stock. We use only first quality frames that are currently being manufactured. No seconds or discontinued frames.

Which lenses should you get?

The doctor has to prescribe the proper power but you as a consumer need to have an idea of the styles of lenses that are available. A recent survey by one of the lens laboratories that I use revealed that there were 37 different single vision lens designs, 63 types bifocals, 29 types of trifocals, 83 designs of progressive lenses and 12 other specialty lenses. That is 224 designs and many prescriptions can be made in each of these types of lenses. The choices are staggering as to the combinations that are possible. This does not include many of the tints and surface treatments that can be applied to the lenses.

Here is a summary of ophthalmic lenses.

Single Vision:

This lens has the same power all the way across the lens. They are for the patient that can focus their eyes from distance to near in a normal manner. They vary in the type of material and curvature. The materials are glass, resin plastic and polycarbonate plastic.

Progressive lenses:

This lens was first designed in France in the 1960's and iss meant to replace the bifocals and trifocals. There is more than one power in the lens yet looks to the rest of the world that it is a single vision. The lens works by having a variable curvature in the lower part of the lens and blending the curvatures together to minimize distortion. As you can see by the large numbers of designs that are available with progressive lenses, there is a lot of effort being spent to perfect this design. These lenses look to others as identical to single vision There are no lines.

Bifocal:

These lenses are the basic lens for people who need more than one focus in each lens. They provide an additional power so that near images can be seen clearly. The second lens is imbedded in the main lens and are of various shapes and styles depending on how the lens is to be used.

Trifocal:

The trifocal lens is similar to the bifocal. They use three lenses set to give two additional powers in addition to the main power of the lens. Typically this lens is used for older individuals who need clear vision at both 16 inches (40cm) and at arms length.

Which lens is best?

If you can wear a single vision lens comfortably at all distances then it is usually the best for you. The simplest lens that works for the patient is usually the best. Many people that do near work on a regular basis may need a multifocal (bifocal, trifocal or progressive).

What should you know about optics:

One of the most important factors in a lens is its ability to bend light. It is measured as the index of refraction. The higher the index of refraction will bend light more, making the lens thinner but will also increase the distortion present in the optics. The range of index of refraction for lenses is from 1.49 to 1.8

Now pick a material.

Lenses can be made of various materials. They include Plastics like resin and Polycarbonate and Trivex. There are also several types of glass available.

Resin Plastic:

This material is available from various manufacturers in the widest array of designs. It has good optical characteristics and is light weight. It is scratch resistant.

Polycarbonate:

This thermal plastic is of higher index and is very light weight. It is very tough and nearly unbreakable but softer and prone to scratches. It is the recommended lens for active people as it so tough. It will withstand over nine times the impact of a tempered glass lens

Glass:

Glass has long been a lens material. Its usage has decreased dramatically in the last several years. The major reasons for the decline of glass as a lens is because it is very heavy compared to other materials and it is the most brittle product to make a lens from. Being brittle means that it is most easily broken and requires special tempering to pass a United Stated government mandated impact test. The range of index of refraction is from 1.52 to 1.80.

Tints:

Tints are used to block some of the light energy. For most people this means to reduce the visible light. There are tints that can block the ultraviolet (UV) light or even x-rays. Too much visible light is a problem for many people. A plastic lens will block out most of the UV light without any special treatment. There are special UV tints available for almost any lens that can block out over 95% of the UV light.

Photochromic:

The term photochromic means to change color with light. Specifically there are lenses that become darker when struck by UV light. Since the sun is the major source of UV, lenses can be designed to darken outside. This is available in glass and resin plastic lenses. Brand names include Transitions and Photogrey.

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