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Husband Patrick's eyes are beginning to have that squinty Clint Eastwood look that his father's eyes have. Crow's-feet are starting to appear on my sugar lump's face. He needs sunglasses to slow down their onset, but I didn't want to buy him cheapies and damage his vision. I sought advice from a pro.

"People should always wear sunglasses whenever they are outside," said optician Michael Emerson, of Hart Optical Company in La Mesa. "Ultraviolet radiation comes through on cloudy days as well as sunny days, and it causes sun cataracts. A cataract is a clouding of the crystalline lens, which is the lens in the eye that does all the heavy lifting as far as vision. Over time it becomes less clear and more opaque and the patient eventually has to have it removed."

Bad sunglasses, Emerson warns, are worse than nothing. "If the lens is plastic, just the fact that it is a plastic lens, it's probably going to block 40 percent of the UV. But 60 percent is still getting through, which is the bad part, because if there's any tinting at all on a lens it causes the human eye to dilate. And as the eye dilates, it's going to try to let in more light. The human eye is a pretty good little instrument and it will protect itself. But if you fake it out with a bad pair of lenses, you think you're protecting your eyes, but you're not. You are frying that retina and then frying that crystalline lens."

Besides high percentage UV protection, Emerson says a quality lens is also important. "A good optical quality lens, even in a nonprescription pair, means no warpage. Off-the-rack sunglasses have warped lenses. Warped lenses will cause eyestrain. It is like looking through a shower door; you can see but not clearly, and you don't know why. As you move your head side to side, sometimes you can see the warpage. Or you can hold the glasses out in front of you at arms length and move them side-to-side on a straight edge or a straight wall and you can see the wall curve. Those are distorted lenses; you don't want to wear those either."

How dark should the sunglasses be?

"I recommend only purchasing enough tint to get the job done. Don't go and get the darkest sunglasses you can find. I like to let the human eye do some of its work. I want the pupil to open up to have more good light get in there so that they can see. You want to have good contrast, enough light in there, but not so much that you are squinting. The basic industry standards for putting a tint on sunglasses are a one, two, or three tint. One is a tint that you could almost wear indoors; two is a tint that you wear outdoors -- it's better outdoors than indoors; three is pure outdoor tint."

Emerson hesitated to recommend any brand. "There are thousands of brands that are good, and there are thousands of brands that are not," offered Emerson. "Generally a person is safe by going to an optical store to buy their sunglasses as opposed to buying off the rack. Off-the-rack lenses are not regulated by the Board of Medical Quality Assurance or the FDA."

Emerson did warn against clip-on sunwear sold at optical stores. "What we call solar shields and clip-ons, some of them are not very good quality. For somebody who doesn't want to spend more than $20, that is what they're going to get. For a decent frame and a decent lens -- single vision, no bifocal -- you are probably looking at about $200."

A lot of nonprescription sunglasses are made with polycarbonate lenses, said Emerson. "You get your worst light transmission through polycarbonate materials. When light starts going through it, as you slow it down, it starts to break up into the rainbow, the chromatic aberration. Polycarbonate is about as slow as you can go before light will break up into the rainbow. And then once it does that, it is no longer usable as a medium for looking through. Generally, polycarbonates are used for people with thick, thick prescriptions, to control edge thickness."

But when it comes to UV protection, Emerson said, "polycarbonate-tinted lenses are probably the worst visual thing to look through, but it is one of the best protections against UV rays. The next best thing would be a polycarbonate-tinted sunglass lens with an antireflection coating on it, which enhances the visual part that you are losing because of the poly material. The coatings, however, scratch easily. They are hard to take care of, and they raise the price by about $60. The next-best-quality lens after that would be a mid-index lens, and put the tint and the antireflection on that. That will run about $200 a pair. The next level up is a Polaroid, which is a lens that neutralizes glare in the vertical meridian 100 percent. A Polaroid lens has one of the best sunglass-glare protections we know of right now."

When I told Emerson that I'd almost rather get cataracts than spend $200 on a pair of sunglasses, he responded, "Then get the UV A, B, and C radiation protection. But remember, the cheaper the glasses, the more flaws you're going to buy. You're going to buy warps and poor index. Whatever you buy, you want to have a UV rating with a number. And most good optical quality retailers have UV meters in their store and they can check your lenses."

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