Aging often brings a reduction in the ability to see well in low light.

Reasons: Night vision has two elements. First, the pupils must dilate to let in as much light as possible. Normally this happens within seconds of entering a darkened environment-but as we age, the muscles that control pupil dilation weaken, slowing down and/or limiting dilation. Second, chemical changes must occur in the light-sensitive photoreceptors (called rods and cones) of the retina at the back of the eyeball. Some of these changes take several minutes and some take longer, so normally full night vision is not achieved for about 20 minutes. Even brief exposure to bright light (such as oncoming headlights) reverses these chemical changes, so the processes must start over. With age, these chemical changes occur more slowly... and some of our photoreceptors may be lost.

While we cannot restore the eyes' full youthful function, we can take steps to preserve and even improve our ability to see in low light. Here's how...

First, see your eye doctor to investigate possible underlying medical problems. Various eye disorders can cause or contribute to reduced night vision, including cataracts (clouding of the eye's lens), retinitis pigmentosa (a disease that damages the retina's rods and cones) and macular degeneration (in which objects in the center of the field of vision cannot be seen). Night vision also can be compromised by liver cirrhosis or the digestive disorder celiac disease, which can lead to deficiencies of eye-protecting nutrients... or diabetes, which can damage eye nerves and blood vessels. Diagnosing any underlying disorder is vital because the sooner it is treated, the better the outcome is likely to be.

Adopt an eye-healthy diet. Eat foods rich in the vision-supporting nutrients below... and ask your doctor whether supplementation is right for you. Especially important...

• Lutein, a yellow pigment and antioxidant found in com, dark green leafy vegetables, egg yolks, kiwi fruit, oranges and yellow squash. Typical supplement dosage: 6 milligrams (mg) daily.

• Vitamin A, found in carrots, Chinese cabbage, dark green leafy vegetables, pumpkin, sweet potatoes and winter squash. Typical supplement dosage: 10,000 international units (HJ) daily.

• Zeaxanthin, a yellow pigment and anti-. oxidant found in com, egg yolks, kiwi fruit, orange peppers and oranges. Typical supplement dosage: 300 micrograms daily.

• Zinc, found in beans, beef, crab, duck, lamb, oat bran, oysters, ricotta cheese, turkey and yogurt. Typical supplement dosage: 20 mg daily.

• Update prescription lenses. Many people just keep wearing the same old glasses even though vision tends to change over time, Dr. Grossman said-so new glasses with the correct prescription often can improve night vision.

• Keep eyeglasses and contacts dean. Smudges bend rays of light and distort what you see.

• Wear sunglasses outdoors on sunny days, especially between noon and 3 pm. This is particularly important for people with light-colored eyes, which are more vulnerable to the sun's damaging ultraviolet rays. Excessive sun exposure is a leading cause of eye disorders (such as cataracts) that can impair eyesight, including night vision. Amber or gray lenses are best for sunglasses, Dr. Grossman said, because they absorb light frequencies most evenly.

• Do not use yellow-tinted lenses at night. These often are marketed as "night driving" glasses, implying that they sharpen contrast and reduce glare in low light. However, Dr. Grossman cautioned that any tint only further impairs night vision.

Safest: If you wear prescription glasses, stick to untinted, clear lenses-but do ask your optometrist about adding an antireflective or antiglare coating.

• Exercise your night vision. This won't speed up the eyes' process of adjusting to the dark, but may encourage a mental focus that helps the brain and eyes work better together-thus improving your ability to perceive objects in a darkened environment.

What to do: For 20 minutes four times per week, go into a familiar room at night and tum off the lights. As your eyes are adjusting, look directly toward a specific object that you know is there... focus on it, trying to make out its shape and details and to distinguish it from surrounding shadows. With practice, your visual perception should improve. For an additional challenge, do the exercise outdoors at night... while looking at unfamiliar objects in a dark room... or while using peripheral vision rather than looking directly at an object.

• When driving at night, avoid looking directly at oncoming headlights. Shifting your gaze slightly to the right of center minimizes the eye changes that would temporarily impair your night vision, yet still allows you to see traffic.

Also: Use the night setting on rearview mirrors to reduce reflected glare.

• Clean car windows and lights. When was the last time you used glass cleaner on the inside of your windshield... or on rear and side windows... or on headlights and taillights? For the clearest possible view and minimal distortion from smudges, keep all windows and lights squeaky clean.

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