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Seeing in the Dark

It happens to the best of us; you get prepared for bed, and you turn the lights off, but you can't fall asleep. You open your eyes and all you see is black. You notice that it's difficult to see anything for a couple of moments before the room becomes visible again. This process, ''dark adaptation,'' allows our eyes to see even when it's really dark.

Many people don't know that night vision relies on the cooperation of physical, neural and biochemical mechanisms. So how does this work? Every 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 that helps the eye detect light and color. Cones and rods are distributed evenly throughout your retina, except for in the small area opposite the pupil known as the fovea, where there are only cone cells. The fovea provides detailed vision, such as when reading. You might already be aware that the details and colors we see are detected by cone cells, while the rods are sensitive to light and detect movement.

How does this apply to being able to see in the middle of the night? When struggling to view something in the dark, like the dresser in your darkened room, you'll be better off if you focus on something off to the side of it. Since there no rods in the fovea, you'll see better if you avoid using it when it's dim.

Another way your eye responds to darkness is by your pupils dilating. Your pupil reaches its maximum size in about a minute; however, your eyes will get better at seeing in the dark over a half hour period and, as everyone has experienced, during this time, your ability to see in the dark will increase remarkably.

Here's an example of dark adaptation: when you enter a darkened movie theatre from a well-lit lobby and have a hard time finding somewhere to sit. After a while, your eyes adapt to the situation and before you know it, you can see. You'll experience the same thing when you're looking at the stars in the sky. At the beginning, you won't see many. As you keep gazing, your eyes will dark adapt and millions of stars will gradually appear. It takes a few noticeable moments until your eyes fully get used to normal indoor light. Then if you go back outside, those changes will be lost in the blink of an eye.

This is one reason behind why many people have difficulty driving their cars at night. When you look right at the ''brights'' of an oncoming car in traffic, you may find yourself briefly blinded, until that car passes and your eyes once again adjust to the night light. A helpful way to avoid this is to avoid looking right at the car's lights, and learn to try to allow your peripheral vision to guide you.

If you're finding it challenging to see at night or in the dark, call us to schedule a consultation with our doctors who will be able to shed some light on why this is happening, and rule out other and perhaps more serious reasons for worsening vision, like macular degeneration or cataracts.

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