Index Eyeglasses: Choosing Lenses
When you get new glasses, there are three important things you need to know about lenses:
- the kind of lenses (single vision, bifocal, trifocal, or progressive)
- the lens material (glass or plastics)
- coatings applied to the lenses (such as coatings to prevent reflection, scratches, or glare)
What lens design is right for me?
Your eye care provider will advise you about the type of lens. Most people get either single-vision lenses or multifocal lenses.
Single-vision lenses correct a single vision problem, such as farsightedness.
Multifocal lenses correct more than one vision problem (such as reading vision and distant vision). 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 close-up vision part at the bottom of the lens has one of the following shapes at:
- A half-moon, or sideways D-shape. This is the most common type of bifocal.
- A narrow rectangular area, like a ribbon.
- A circle shape.
- A full bottom half of a lens.
Some glasses can have the close-up vision in a different shape and place. For example, electricians who look up to do close work with wires may have the close-up vision at the top of the lens).
- Trifocals: These are just like bifocals, except the lens is divided into 3 sections. The top is for distance, the middle for middle vision, and the bottom for close-up vision. Visible lines divide the sections. The mid-range of trifocals is used to focus on something about an arms-length away, such as a computer screen.
- Progressive lenses: Progressive lenses have no line in the lens dividing the sections. Instead there is a smooth transition between the sections of the bifocals or trifocals. 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. It takes some time to adjust to wearing progressive lenses.
Children rarely need multifocal lenses. If they do require multifocal lenses, your eyecare provider will tell you which ones to get.
What materials are used for 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, and have a risk of shattering.
- 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 and lighter 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.
- 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 they 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 a shatter-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, you should also get special frames that are impact resistant.
- If your child has poor vision in one eye for any reason, your provider may suggest that your child wear polycarbonate lenses to protect the good eye. If your child doesn’t need glasses to see well, you can get a pair of polycarbonate lenses without any prescription in them. These look like prescription glasses, but are meant to protect your child’s eyes rather than to improve your vision.
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 coating is very helpful for plastic lenses, which are more likely to scratch 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 the 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 for people who are sensitive to light.
Reviewed for medical accuracy by faculty at the Wilmer Eye Institute at Johns Hopkins. Web site: http://www.hopkinsmedicine.org/wilmer/ Developed by RelayHealth. Published by RelayHealth.
Last modified: 2011-02-11
Last reviewed: 2010-10-27 This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional. References
Pediatric Advisor 2011.4 Index
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