Choosing Lenses for Eyeglasses

Buying eyeglass lenses requires making decisions about the design of the lenses, the lens material, and any coatings you may want applied to the lenses.

What lens design is right for me?

Your eye doctor has probably already recommended the type of lens design. Most people get either single-vision lenses or multifocal lenses.

Single-vision lenses are for correcting a single vision problem. The entire lens has only one correction on it.

Multifocal lenses correct more than one vision problem (such as nearsightedness and presbyopia). There are different types of multifocal lenses, for example:

• Bifocals: Lenses for these glasses are divided in two. The top part is for distance vision and the bottom part is for close vision. You can see the 2 segments on the glasses because there is a line dividing the area.

  Usually the segment for close-up vision has one of the following shapes at the bottom of the lens:

  • A half-moon, also called a flat-top, straight-top, or D segment. This is the most common type of bifocal.
  • A narrow rectangular area, also called a ribbon segment.
  • A round segment.
  • A full bottom half of a lens, called the Franklin, Executive, or E style.

  Sometimes you may customize your glasses by having the part of the lens for close-up vision in a specific shape and place (for example, a small segment at the bottom corner of the lens for golfers or a segment at the top of the lenses for electricians who look up to do close work with wires).

• Trifocals: These are just like bifocals, except the lens is divided into 3 sections. The top is for distance, the middle for intermediate vision, and the bottom for close-up vision. Visible lines divide the sections. These can be useful for people who need to work or read at 2 distances, like a pianist who reads music at a different distance then she reads books.
• Progressive lenses: Progressive lenses have no line in the lens dividing the sections. Instead there is a smooth transition between the sections of the lens. These are available for bifocal and trifocal prescriptions. There is some distortion on the outer edges of the lenses. You get the best vision when you point your nose directly at what you want to see. You will need some time to adjust to wearing progressive lenses.

What materials are used for lenses?

Glass lenses

• Regular: Glass lenses are not as easy to scratch as plastic lenses. They also can be used for many types of prescriptions. However, they are heavier than plastic lenses.
• High-index or aspheric: Glass lenses can also be made from a special type of glass called high-index. This type of material is compressed so that it uses less material than regular glass lenses. High-index lenses are much thinner than normal lenses and can be great for people who have a strong correction and would usually need very thick glasses. Aspheric lenses use the high-index material as well as special design techniques to make the lenses thinner. High-index lenses have built-in protection against ultraviolet (UV) rays.

Plastic Lenses

• Hard resin: Hard resin lenses are half the weight of glass. Hard resin lenses are more easily scratched than glass, but they are durable.
• High-index or aspheric: High-index plastic lenses work the same way as high-index glass lenses. These lenses are made from a compressed material so that strong corrections can be made thinner. Aspheric lenses use the high-index material as well as special design techniques to make the lenses thinner. High-index lenses may be good for people who have a very strong correction because the lens can be made much thinner than if made from hard resin. High index lenses have built-in protection against ultraviolet (UV) rays.
• Polycarbonate: This is an extremely impact-resistant material. It is best for kids, athletes, or people who need safety glasses for work. Polycarbonate lenses are another type of high-index lens and are light and comfortable. They also have built-in UV protection. For the best protection, special frames that are impact resistant are also recommended. If you have poor vision in one eye for any reason, your eye doctor may recommend that you wear polycarbonate lenses to protect the good eye. If you don't need glasses to see well, you can get a pair of polycarbonate lenses without any prescription in them.

What treatments are available for lenses?

• Antireflective coating: This coating reduces glare. However, you need to take extra care of your glasses to keep the coating from wearing away. When the coating wears off, the glasses may not work as well.
• Scratch-resistant coating: This is a protective coating. It is especially helpful for plastic lenses, which are more prone to scratches than glass.
• UV coating: This coating helps protect your eyes from the sun's harmful ultraviolet rays. You can get a UV coating on both tinted and clear lenses. Polycarbonate and high-index lenses already have UV protection.
• Mirror coating: These coatings come in several colors and prevent people from seeing your eyes. This coating helps protect your eyes against glare from surfaces such as water or snow.
• Polarized lenses: This treatment is good for outdoor wear. It helps cut down on glare and gives better clarity and depth perception.
• Tinted lenses: Most lenses can be tinted in a variety of colors.
• Photochromatic lenses: These lenses automatically darken when you go outdoors and return to normal when you go back indoors. They may be more comfortable, especially for people who are sensitive to light.