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Night Vision

Some nights, you lie in bed with the lights off, but you just can't seem to doze off. You open your eyes and all you see is black. You need several moments to get used to the dark and then objects in the room begin to re-appear. This process is known as ''dark adaptation'' and it's what makes our eyes see in the dark.

In order for night vision and dark adaptation to work, many physiological, neurological and biochemical mechanisms must take place behind the scenes. So how does this work? The retina is a layer of cells at the back of the eye. The section of the retina across from the pupil that is responsible for the point of focus is called the fovea. The retina comprises cone cells and rod cells, named for their respective shapes. The rods are able to function more efficiently than cone cells in low light conditions but those cells are absent from the fovea. What's the difference between these two cell types? In short, details and colors we see are detected by the cones, while rod cells are sensitive to light and detect movement.

This information is significant because, when looking at an object in the dark, like the dresser in your darkened room, instead of looking directly at it, try to use your peripheral vision. By looking to the side, you take advantage of the rods, which work better in the dark.

Another method by which your eye responds to the dark is by your pupils dilating. It requires less than a minute for your pupil to fully enlarge but dark adaptation continues to develop over roughly a 30 minute time period. During this time, light sensitivity increases by a factor of 10,000 or more.

Here's an example of dark adaptation: when you exit a bright area and enter a dim one, for example, when coming inside after being out in the sun. It takes a few noticeable moments until your eyes fully get used to regular indoor light, but if you walk back out outside, those changes will disappear in the blink of an eye.

This explains one reason behind why a lot people have difficulty driving at night. If you look right at the headlights of opposing traffic, you are momentarily blinded, until that car is gone and you readjust to the night light. To prevent this, try not to look right at headlights, and instead, use peripheral vision to observe oncoming traffic at night.

There are several conditions that could contribute to difficulty seeing in the dark. These include not getting enough Vitamin A in your diet, cataracts, glaucoma, or some other visual interference. If you detect that you have trouble in the dark, schedule an appointment with one of our eye care professionals who will be able to identify and rectify it.