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Eyeglasses and eyeglass lenses: Q&A

Q: I just got new polycarbonate lenses. What is the best way to clean them, and with what? They seem to already have small dots all over them, maybe from spray paint where I work. — T.H., Ohio

A: My staff tells me you can use rubbing alcohol on the front surface, but not on the back. Use it sparingly, especially if you have AR (anti-reflective) coating. Another very simple trick is lightly using your fingernail if there are only a few spots.

Our high tech coatings are wonderful, but they are susceptible to failure when attacked by good, old-fashioned stuff like paint and other toxic chemicals. — Dr. Dubow

Q: I have 20/40 vision in one eye, and 20/50 in the other. My doctor insists that I get glasses, but I feel no need for it. I never feel any strain (or get headaches) when reading or working on the computer.

It is my understanding that most people who get glasses get used to them and are unable to do without them — something I would like to avoid. Besides, isn't 20/40 considered a good eye surgery result? — L., New Jersey

A: "Good" vision is subject to personal interpretation. With your type of vision and no symptoms, you will not harm your eyes by not wearing glasses. But, you are missing out on a lot by being blurry! And your driving, especially at night, is extremely risky for you and those of us on the highway with you!

It is a common misperception that wearing eyeglasses makes your eyes worse, to a point where you cannot go without the glasses. There is no permanent vision change caused by wearing glasses. Your brain does lose its "blur adaptation" temporarily, which is how you compensate for seeing badly, but it comes back if you go without glasses for a while.

So, it is your choice to be blurry. But remember, you don't have to wear your glasses all the time — how about just for driving, movies, etc.? — Dr. Dubow

Q: What type of eyeglass lenses would you recommend to correct -8.5 defect in the most aesthetically pleasing way, and would I have to sell my house to buy them? — J.L., Manchester, England

A: It depends on the value of your house!

Seriously, there are aspheric high-index lenses and polycarbonate lenses that could be made very thin in your prescription if you chose the right frame.

I recommend the smallest frame possible (that looks good on your face). I also recommend a frame that is fairly round or oval (no corners), where you look right through the center of each lens. These techniques minimize lens thickness.

I'd also recommend an anti-reflective coating on the lenses. You'll look great... and you won't have to sell your house! — Dr. Dubow

Q: Is there a lens available for farsighted people that doesn't magnify the eye? I hate that effect and won't wear glasses because it is so unattractive. — L., West Virginia

A: There are now lenses called aspheric lenses that don't magnify the eye as much as previous lenses did. They can look really great, as well as having less distortion. You'll love them! — Dr. Dubow

Q: I have a +4.00 prescription in my left eye and a -2.00 in my right. What lenses are available to make my left eye appear normal in size when wearing glasses? Please respond. I am very self-conscious while wearing my glasses. — G.R., New York

A: I understand your feelings. Luckily there are some new spectacle lens designs that can help you. In particular, ask about aspheric and high-index lenses. Also ask your eyeglass provider to equalize the thickness as much as possible between the two eyes.

I would also recommend you consider contact lenses. They will equalize the image sizes on your retinas and potentially give you much better balance between the two eyes. — Dr. Dubow

Q: I recently purchased high-index plastic lenses and cannot see as well as with my previous plastic lenses. My distance vision and peripheral vision are much poorer. My optometrist thinks it may be the new material. What do you think? — A.G., California

A: Could be the material. It could also be the position of the lenses on your face, the angle of the glasses, the size of the lenses, etc. There are a number of thin and light materials on the market. If nothing makes this problem better, perhaps you should try a different one. — Dr. Dubow

Q: Are you familiar with the high-index glass materials from Zeiss and Corning (up to 1.9)? I have a prescription of approximately -8.5/-3 and 9.25/-3. The frames I'm looking into are size 38 to 40. Based on my research, the advantages of plastic (lighter, shatter-resistant) may not be an issue with the high-index and lens size. I've been told that Corning lenses are tempered and ball dropped. — P.C., Delaware

A: I agree. Modern high-index glass lenses can be thin, light and safe. However, in my opinion, polycarbonate lenses are safer. — Dr. Dubow

Q: What is the best eyeglass tint? — B.H., Idaho

A: Really and truly, there is no best tint. Different tints help with different things. There are some tints that help shooters, some that help golfers, some that help tennis players, some that help computer users, etc. But each person is different. Go to a good optical shop and talk to a trained optician who can help you figure out what would be best for you. Also, ask about photochromic lenses. These light-sensitive lenses darken automatically in response to sunlight and are available in a variety of colors. — Dr. Dubow

Q: I have recently purchased new glasses. My lenses are "mid" index, and for the first time I got the anti-reflective coating. This is my second week wearing them, and in bright light, if I'm not looking directly through the center, I see a thin halo-type effect of blue and yellow on either sides of objects — even on my computer screen. Is this normal, or are the lenses defective? — L.G., Canada

A: In my experience, anti-reflective (AR) coatings do not cause this to occur. You may see a shimmery colored coating when looking at the fronts of the lenses, but not usually while wearing them and looking from the back. The index may be causing this phenomenon — I'm not sure. It's possible it's just normal distortions caused by looking off-center. — Dr. Dubow

I recommend you go back to where you got your glasses and let them figure this one out! — Dr. Dubow

Q: Please explain all the numbers and terms on my eyeglass prescription. Thank you. — B.J., Texas

A: An eyeglass prescription is written in a standardized format with standardized notation so it can be interpreted worldwide. Let's look at one and break it down:

-2.00 -1.00 x 180. The first number (-2.00) tells us the spherical refractive error (farsightedness or nearsightedness). In this case, because there is a minus sign in front of the 2.00, this patient is nearsighted. A plus sign would indicate farsightedness.

The second number (-1.00) is the astigmatism. If there is no astigmatism, we generally write the letters DS or SPH after the first number to let the optician know that we didn't just forget to write in the astigmatism.

The final number (180) is the direction of the astigmatism. Astigmatism, an oval-shaped eye, can be measured in any direction around the clock. We use the numbers from 1 to 180 to indicate the orientation of the oval shape.

There may be additional numbers in a glasses prescription. For instance, if the basic prescription is followed by a small number with a superscript (1^) it indicates prism correction. There may be more than one set of prism numbers for each eye.

If you are over age 40 and have presbyopia, there may be numbers on your prescription that describe the added magnifying power prescribed for progressive lenses or bifocals so you can see clearly up close. These "add powers" usually go from +0.75 to +3.00, depending on your age and visual needs.

Finally, your eye doctor may indicate that anti-reflective (AR) coating should be applied to the lenses. This microscopic coating eliminates distracting reflections for the clearest, most comfortable vision possible.

By the way, the letters OD and OS on your eyeglass prescription indicate which eye each string of numbers is for. OD stands for right eye and OS for left eye, while OU means both eyes. — Dr. Dubow

Q: What is the best possible type of eyewear to wear while driving at night to eliminate glare from other vehicles' headlights? — R.B., New Jersey

A: Easy! Get lenses with anti-reflective coating. This coating reduces glare by 90 percent or more and works great. I never get glasses without it! — Dr. Dubow

Q: Can you tell me what the difference is between anti-reflective lenses and polarized lenses? No one seems to want to, or perhaps they're just not able to answer this question for me. — D.L., New York

A: Anti-reflective lenses simply cut out most of the reflections caused by light bouncing between the two lens surfaces and interfering with good, comfortable vision.

Polarized lenses cut out light from one whole meridian, typically the horizontal one. This minimizes the glare from light that bounces off water, the hood of your car, or a shiny road surface.

Polarization is useful for fishermen or people that do a lot of driving, though many outdoors people prefer polarized sunglasses.

Polarization is usually applied only to sun lenses, whereas anti-reflective coatings can be used on both indoor and outdoor glasses with success. — Dr. Dubow

Q: I recently went to my local optometrist for new frames and lenses. By the time I left his office I had "the best" progressive lenses, titanium frames, scratch coat, AR coating and a bill for over 420 bucks.

Three weeks later I brought the pair of glasses back to the OD due to scratches on the lenses and was told he would split the cost with me for replacement lenses.

Is this any way to treat a customer? I did not drop my glasses or take a sledgehammer to them. I thought I paid extra for the scratch coating so I wouldn't have this problem. Is this common practice for an OD today? — K.F., New Jersey

A: Good question! Although I hesitate to speak against a colleague, it is my view that new and exciting technology should not take the place of customer service.

A lot depends on how you define "recently." If you bought your glasses within the past three to six months, it is my opinion that your doctor should have used the warranty given to him or her by the laboratory that supplied the lenses.

If your problem happened a year ago, then the offer to split the cost is probably fair depending on what caused the scratches. Circular scratches usually indicate that the patient used the wrong cleaning cloth or forgot to rinse dirt particles off the lenses before rubbing.

Most importantly, if you are unhappy be sure to tell the doctor. Most private practitioners are very tuned in to their patients' complete satisfaction. And remember, it is best to use an appropriate cleaning solution and cleaning cloth on your high-tech lenses. You can also clean your lenses with warm water and a mild detergent and dry them with a clean cotton dish towel. — Dr. Dubow

Q: What is "prescribed prism?" Why is it necessary, and how does it help me see? — J.C., Colorado

A: Prism is usually prescribed in lenses to help you use your eyes together. Some people's eyes have a tendency to try and pull apart when they are in use — some go up and down, and some go in, and some go out. These are called muscle imbalances, or "fixation disparities," in our lingo.

Prism can help ease the symptoms of these imbalances by making the brain think the eyes are working together. I have worn prism in my glasses since about age 5, and I prescribe prism for many of my patients, with very positive results. In my opinion, you have a great eye care practitioner! — Dr. Dubow

Q: I have a "prism" in my glasses, which is to help with the fact that I don't do the "lining up the horizontal/vertical bars" portion of the eye exam correctly. I would like to have my eyes fixed, but my doctor says that LASIK can't fix this condition and I'd have to wear glasses when I do computer work anyway.

Is this true? I am in computer sales, so I use one ALL day long. Any ideas? Thanks! — J.P., Kansas

A: Take a look at my explanation of prism above. I have found that some of my patients who require prism can get along just fine after refractive surgery, while others require glasses for some tasks.

I can't agree or disagree with your doctor without having examined you myself.


But before you jump on a plane to Minnesota, remember that you will have to wear glasses again anyway as you age — unless you have a monovision correction.

I suggest you get a second opinion on your prism and have a frank discussion about the pros and cons of refractive surgery with a practitioner you trust. — Dr. Dubow

[See also: free eye exams and eyeglasses for qualifying individuals]

Q: I have double vision and would like to know how prism in glasses helps to cure this. Also, is there any way I can wear contacts to correct this? — Tina, Florida

A: A prism bends light. Prism in glasses can kind of fool your eyes into thinking they are working together without strain. Prism can also help with double vision by aligning the two images into one.

I prescribe a lot of prism for my patients, with excellent results.

Some patients who require prism can wear contact lenses, and some can't. It depends on the kind and the amount of the prism.

In fact, some kinds of prism are corrected better by contact lenses than by glasses! See your eye care practitioner for more details. — Dr. Dubow

Q: What are prisms? How do they work? — B.M., Arizona

A: Prisms bend light and separate white light into its component colors. In vision correction, we like the light bending and don't want the color separation aspects of prism.

How do prisms work? It's complicated, but if you think of a prism as being a triangle pointing upwards, light goes in one side, bends down toward the base, and comes out the other side going in a different direction. Of course, in glasses and contact lenses this is much more sophisticated and doesn't really look like a triangle... but the effect is the same.

Prisms are used in lenses to help keep the eyes working together and aligned. They can make the difference between glasses that are OK and glasses that are wonderful. — Dr. Dubow

Please note: If you have an urgent question about your eye health, contact your eye care practitioner immediately. This page is designed to provide general information about vision, vision care and vision correction. It is not intended to provide medical advice. If you suspect that you have a vision problem or a condition that requires attention, consult with an eye care professional for advice on the treatment of your own specific condition and for your own particular needs. For more information, read our Terms of Use.

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