Dear Doctor: About a year ago, when I turned 44, I started using reading glasses that I purchased at the drugstore. They seemed to work just fine. Now I need a stronger pair, and I wonder whether using them has weakened my eyes.

Dear Reader: We're happy to reassure you that using over-the-counter readers -- or any kind of corrective lenses, for that matter -- will not weaken or damage your eyesight. However, the fact that you find you need to move to a higher level of magnification does indicate that your vision is changing. And considering that many adults begin to experience changes to their ability to see clearly at close range after age 40, it's not all that surprising.

This change in close focus is known as presbyopia, which occurs when the lens within your eye gradually becomes less flexible. This is believed to be the result of age-related changes to the proteins within the natural lens in the eye, and to the tissues of the surrounding muscles that cause the lens to focus. The loss in flexibility to the natural lens results in blurred vision when doing close-focus activities such as reading.

While you could certainly opt to buy a new pair of drugstore reading glasses with a higher level of magnification, we recommend that you use this shift in vision as an opportunity to visit an eye care professional.

One-size-fits-all reading glasses are certainly affordable, and a quick trip to the store is more convenient than a medical appointment. But chances are the generic readers will not correct your eyesight to the highest level of accuracy. That's because, for most of us, the prescription in each eye is at least slightly different. Many individuals also have a small amount of astigmatism correction in their prescriptions as well. Wearing the wrong glasses can lead to headache and fatigue as your eyes strain to achieve optimal focus.

A comprehensive eye exam not only yields a corrective prescription tailored to your specific needs, it also includes several other tests to detect vision problems, assess eye health and screen for eye disease. For example, your eye care professional will use special drops to dilate your pupil and examine the important tissues at the back of the eye, including the retina, the macula and the optic nerve. A test of the pressure within the eye, known as tonometry, screens for glaucoma.

If you already wear glasses to correct farsightedness, you have the option of blending the two prescriptions in a pair of bifocals, trifocals or progressive lenses. A pair of multi-vision glasses for life on the go, and a pair of reading glasses for sustained close work, will give you the best of both worlds. If you prefer contact lenses, multifocal contacts correct near, intermediate and far vision.

Age-related changes to vision, once begun, will continue. However, these changes can occur so gradually that they may be difficult to notice. That's why it's important to schedule regular eye exams and safeguard your vision.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I'm leery of sleep drugs, so I've been taking Benadryl to help me sleep. Now I read that it should be taken only for a limited time. What's the story on this drug?

Dear Reader: Diphenhydramine HCL, or Benadryl, is a sedating antihistamine. The medication has been used since 1946 for allergies, but because it is sedating, or sleep-inducing, people have also used it to help them sleep. Unlike the allergy medications Claritin, Zyrtec or Allegra, this medication blocks histamine receptors in the brain. Histamine is necessary to promote wakefulness, motivation and goal-directed behaviors; when the receptors for histamine are blocked, drowsiness occurs. Many companies have marketed diphenhydramine and doxylamine (another sedating antihistamine) for insomnia under different brand names.

Researchers have conducted many studies of diphenhydramine for insomnia, but most have been small. One of the larger studies looked at individuals with an average age of 44 years who had mild insomnia. In this study, people either took diphenhydramine or a placebo. The diphenhydramine group switched to a placebo after two weeks. The participants kept diaries of how long it took them to fall asleep, their total sleep time and the number of times they awoke.

Researchers found no difference between the drug group and the placebo group in the time needed to fall asleep. However, sleep quality improved significantly among those taking the drug. Total sleep time also improved with diphenhydramine, but only by 29 minutes. The authors did not find significant adverse effects and did not find rebound insomnia when the participants stopped diphenhydramine. The authors concluded that, for the short term, the drug does have benefit in treating insomnia.

As for the merits or risks of taking the drug for more than two weeks, there are no good long-term trials of diphenhydramine, and prolonged use raises the potential for problems. Further, two weeks of using sedating antihistamines can create some degree of tolerance to their sleep-inducing effects, so their effectiveness may wane.

In its guidelines for sleep medications, the Journal of Clinical Sleep Medicine does not recommend the use of antihistamines for chronic insomnia. Sedating antihistamines can lead to dry mouth, constipation, retention of urine in the bladder, blurred vision and a drop of blood pressure upon standing.

Further, diphenhydramine's half-life, the time it takes for the drug to lose half of its activity, is 9 hours in adults, but 13.5 hours in elderly individuals. That means the drug is still having effects long after one awakes. Sedating antihistamines also can cause grogginess, confusion and memory loss. This is especially concerning in the elderly.

I would re-evaluate whether diphenhydramine is really helping you sleep. You should also consider whether the medication is causing any side effects. Other medications can be used as sleep aids, but the best move, especially for the long term, is to improve your sleep hygiene, such as using the bed for sleep and not for watching television.

If you have trouble doing this on your own, a professional who specializes in sleep therapy might be able to help. Though sleep therapy is a relatively new field, it has shown significant benefits.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Do I really need to take a multivitamin? My sisters are convinced that you can't get all the nutrients that you need without one, but it seems to me that as long you're eating right, you're covered.

Dear Reader: Multivitamins are the most widely used supplements in the United States. It is estimated that between one-third and one-half of all Americans take a multivitamin each day. As a result, your question is one that comes up often in our practices. And while we can't offer specific advice, we can share and explain the information we give to our patients.

The short answer is that for most patients, we believe that if you're eating a balanced diet, one that includes whole grains, a variety of vegetables and fruits, adequate lean protein and dairy products, there is no need for a multivitamin. However, when a patient's diet isn't ideal, then a multivitamin can offer insurance for the deficient vitamins and/or minerals.

Of course, there are exceptions. Pregnant women and women who are trying to become pregnant need at least 400 micrograms of folate per day, a B vitamin that helps to prevent neural tube defects. For these women, a prenatal vitamin or a daily folic acid supplement is recommended. Nursing women have unique nutritional needs that may call for supplementation. Some elderly adults whose appetites have diminished and who therefore don't eat a balanced diet may benefit from adding a multivitamin.

Someone on a restricted diet, such as a vegan, typically needs a B12 supplement. A strict vegetarian may require additional zinc, iron or calcium. And for individuals with chronic conditions such as iron deficiency anemia, B12 deficiency or malabsorption, or a history of gastric bypass surgery, then supplemental vitamins and minerals are necessary to maintaining good health.

So what are vitamins, exactly? They're nutrients that we need in small quantities to maintain various metabolic functions that, when taken in total, add up to good health. Vitamins help the body to produce energy, ward off cell damage, facilitate in the absorption and utilization of minerals, and play varying roles in the regulation of cell and tissue growth.

Vitamins must be taken in food because the body either doesn't produce them in adequate quantities, or doesn't produce them at all. Vitamin D is a bit of an outlier. It's an essential nutrient that does not naturally appear in food in adequate quantities, but is produced when our skin is exposed to the ultraviolet B rays in sunlight. It is also available in fortified foods like milk, fish and mushrooms.

Take an honest look at your diet. If you find some nutritional holes, our advice is to adjust and improve your eating habits. If you do decide to make a multivitamin part of your daily regimen, keep in mind that it cannot take the place of a balanced and healthy diet. Not only do fruits, vegetables, whole grains and leafy greens contain vitamins, they also provide fiber, which is important to good health. Whole foods also contain trace nutrients and other useful compounds that no pill or supplement can re-create.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)