Choosing the Right Lenses
When purchasing eyeglasses, there are many decisions to make regarding the shape, color, size and materials of the frame. But an equally important decision is what lenses and lens treatments you choose, and there are many options here as well.
Here is a brief overview of current lens materials and coatings for you to consider:
High-Index Lenses: Thinner and Lighter
Most people want the thinnest, lightest and most attractive lenses possible in their glasses. If that’s what you’re looking for, you’ll definitely want to consider high-index plastic lenses.
“High-index” refers to the index of refraction of a lens material, which is a measure of how efficiently the material bends (refracts) light to provide a corrective effect. Lenses made with a high-index material require less mass to correct your vision and therefore are noticeably thinner than standard glass or plastic lenses of the same power.
How much thinner? That depends on the value of the refractive index.
Regular plastic eyeglass lenses have an index of refraction of approximately 1.50; standard glass lenses have a refractive index of 1.52. The refractive index of high-index plastic lenses ranges from 1.54 to 1.74, depending on the material.
That might not sound like a big difference, but the higher the index of refraction, the thinner the lenses; and lenses with a refractive index of 1.67 or above are can be less than half the thickness of regular glass or plastic lenses. And because they’re thinner, high-index lenses usually are significantly lighter, too.
Generally speaking, the higher the index of refraction of the lenses, the higher the cost. Your professional optician can help you choose the high-index lenses that give you the best appearance, comfort and value for your prescription.
Note: High-index lenses reflect more light than regular glass or plastic lenses, so an anti-reflective coating is highly recommended for these lenses (see below).
Polycarbonate and Trivex Lenses: Thin, Light and Extra Safe
Polycarbonate and Trivex lenses are special high-index lenses that are thin, light and provide superior impact resistance compared with eyeglass lenses made of other materials. This combination of features makes polycarbonate and Trivex lenses the preferred choice for children’s eyeglasses, sports eyewear and safety glasses.
Polycarbonate lenses are up to 10 times more impact resistant and 20 to 25 percent thinner than regular plastic lenses. They also are up to 30 percent lighter than regular plastic lenses, making them a good choice for anyone who is sensitive to the weight of eyeglasses on their nose.
Trivex lenses provide comparable impact resistance, thickness and weight as polycarbonate lenses, and, like polycarbonate lenses, they block 100 percent of the sun’s harmful ultraviolet (UV) rays — protection that may reduce your risk of developing cataracts or macular degeneration later in life.
Anti-Reflective Coating: Look Better and See Better
All eyeglass lenses reflect some light, which reduces the amount of light that enters the eye to form visual images. These lens reflections can cause vision problems — especially in low-light conditions, like when driving at night.
Anti-reflective (AR) coating eliminates lens reflections and allows more light to enter the eye for better night vision. AR coating also reduces reflective glare and improves visual comfort for tasks like working at a computer.
And AR coating makes eyeglass lenses nearly invisible, improving the appearance of your eyewear and enabling others to see the expression in your eyes, not the reflections in your glasses.
Scratch-Resistant Coating: Protect Your Investment
No eyeglass lenses — not even glass lenses — are scratchproof. But applying a clear, scratch-resistant coating to both sides of eyeglass lenses greatly increases the hardness and durability of the lenses.
Scratch-resistant coatings are essential for all lightweight high-index lenses, which have a relatively soft surface and are easily scratched without added protection.
Nearly all high-index lenses (including polycarbonate and Trivex lenses) come with a factory-applied scratch-resistant coating for added durability. This coating is optional for regular plastic lenses, which have a greater inherent scratch resistance than uncoated high-index lenses. But even regular plastic lenses will be more durable if a scratch-resistant coating is applied.
To further protect your lenses from scratches, keep your glasses in a protective case when you’re not wearing them. Also, never clean your lenses without first rinsing them with an approved cleaning solution or water. Rubbing a dry, dusty or dirty lens with a cleaning cloth or paper towel can cause scratches, even on lenses with a scratch-resistant coating.
Ultraviolet (UV) Treatment: Better Safe Than Sorry
Just as you use sunscreen to keep the sun’s UV rays from harming your skin, UV-absorbing treatments for eyeglass lenses block those same rays from damaging your eyes. Overexposure to ultraviolet radiation is thought to be a cause of cataracts, retinal damage and other eye problems.
Most high-index lenses have 100 percent UV protection built-in. But with regular plastic lenses, a special lens treatment is required to provide complete UV protection. This UV treatment does not change the appearance of the lenses and is inexpensive. Ask your optician for details.
Photochromic Lenses: Automatic Comfort
Photochromic lenses darken automatically when exposed to sunlight, and quickly return to a clear state indoors, making them extremely convenient for anyone who doesn’t want to worry about keeping prescription sunglasses handy for every trip outdoors.
Photochromic lenses also block 100 percent of the sun’s UV rays and are available in a wide variety of lens materials and designs, including bifocal and progressive lenses.
The darkness of most photochromic lenses when they are fully activated depends on how much UV they are exposed to. As a general rule, these lenses won’t get as dark behind the windshield of your car or truck as prescription sunglasses, because the windshield glass of most vehicles blocks out much of the sun’s UV radiation.
Ask For Assistance
Confused? No problem — ask your optician for help and advice when choosing eyeglass lenses to get the best lenses for your needs.
Keep in mind that the best solution for your diverse vision needs often is more than one pair of glasses.
For example, you might want a pair of glasses that feature stylish, sophisticated metal frames and high-index lenses with AR coating for office work and social wear, and a second pair with a lightweight, durable frame and polycarbonate lenses (and AR coating) for sports and active wear outdoors.
Article ©2013, Access Media Group LLC. Source: Choosing Eyeglass Lenses by AllAboutVision.com.