When darkness falls: How to improve your night vision - FOX 21/27 WFXR Roanoke/WWCW Lynchburg News, Weather

By Barbara Kunz, Ph. D.
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Why is it that cats, bats and owls can see so well in the dark - but we can't find our way to the bathroom at night without tripping over the dog? We don't have the same anatomical advantages that some of our nonhuman counterparts do, so we need to rely on nightlights, flashlights and street lights to compensate for our poor night vision.

Seeing light and colors

Our eyes can see a wide range of light. Bright sunlight is about one billion times brighter than the dimmest light in which we can still see. From bright daylight to the dim light of a half-moon, we can see colors and make out fine details.

But when the night sky is overcast or there is less than a half-moon, we no longer see colors and can make out only shades of gray.

All light reaching the eye is focused onto the retina. The retina contains two types of light-sensing cells - rods and cones. The center of the retina has only cones. When light reaches the cones, it is turned into "color" signals. These signals are then sent to the brain. Away from the center of the retina, there are both cones and rods. Rods cannot see colors, but are much more sensitive to light.

Seeing in the dark

Rods and cones need to be recharged after being exposed to light. Until then, a new light signal cannot be sent to the brain. Cones recover quickly. Rods take much longer. This may take minutes, hours or even days.

When you enter a dark area from a well-lit one (such as driving through a tunnel or going into the house after being in the sun), your eyes need to adapt to the low level of light.

Looking at red light doesn't affect night vision, though, because rods are not sensitive to it. If you spend a lot of time driving at night and are looking for a new car, you may want to consider buying one with red dashboard lights.

Improving night vision

The longer the rods have been exposed to light and the brighter it is, the longer it takes to get your maximum night vision. If you know you will have to drive at night, stay inside if possible or wear sunglasses during the day.

Besides avoiding sunlight, there are other ways to improve your night vision. If you are driving, don't look directly at oncoming headlights.

Another tip: When trying to see an object in the dark, don't look directly at it. There are no rods in the center of your retina, so look sideways at the object. The image will become clearer if you use the rods on the border of your retina. This is not easy for most people, so you'll need to practice.

SOURCES:

• National Eye Institute. Night vision. Accessed: 06/24/2010

• American Optometric Association. The eye and night vision. Accessed: 06/23/2010

View the original article on myOptumHealth.com