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A Closer Look at Night Vision

We've all been there; you get all ready for bed, and you turn the lights off, but you just can't seem to doze off. You open your eyes and you can't see a thing. After a few moments you are able to distinguish between the objects in the room and the darkness around you. This process, ''dark adaptation,'' allows people to see even when there's very little light.

Many people don't know that night vision is dependent upon the cooperation of physical, neural and biochemical mechanisms. So how does this work? Your eye has, in addition to other cells, two kinds of cells: cones and rods, on the retina at the back of the eye. Together they form the sensory layer. This is the part that gives your eye the ability to detect light and color. Cones and rods are distributed evenly throughout your retina, save for the small area opposite the pupil known as the fovea, where there are only cone cells. The fovea provides detailed sight, such as when reading. What's the difference between these two cell types? In short, details and colors we see are sensed by cone cells, and the rods are sensitive to light.

How does this apply to being able to see in the middle of the night? When attempting to make out an object in the dark, instead of looking directly at it, try to look just beside it. When you do that, you use the part of the eye that has rods, which, as mentioned above, are more responsive to light, even if there isn't much of it.

Furthermore, the pupils, the black circles in the middle of your eyes, dilate when it's dark. It requires fewer than sixty seconds for your pupil to completely dilate but dark adaptation continues to develop for the next half hour and, as everyone has experienced, during this time, your ability to see will increase enormously.

Dark adaptation occurs when you walk into a dark movie theatre from a well-lit area and have a hard time finding a seat. After a while, you adapt to the situation and see better. You'll experience a very similar feeling when you're looking at the stars in the sky. Initially, you can't see very many. If you keep looking, your eyes will dark adapt and millions of stars will gradually appear. It'll always require a few moments for your eyes to adjust to regular indoor light. Then if you go back into the brightness, those changes will vanish in a moment.

This is actually why many people have trouble driving at night. When you look right at the ''brights'' of a car heading toward you, you may find yourself momentarily unable to see, until you pass them and your eyes once again adjust to the night light. A helpful way to prevent this sort of temporary blindness is to avoid looking right at headlights, and instead, use your peripheral vision to observe oncoming traffic at night.

There are numerous things that could be the cause of decreased night vision. Here are some possibilities: not getting enough Vitamin A in your diet, macular degeneration, cataracts, glaucoma, and others. Should you begin to detect that you experience difficulty seeing in the dark, schedule an appointment with one of our eye doctors who will be able to locate the source of the problem.