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A Closer Look at Night Vision

Imagine there's a blackout and suddenly, you need to find a flashlight or the fuse box. Your eyes normally require a few minutes to adjust to the dark and then you can see again. This remarkable process is ''dark adaptation''.

In order for night vision and dark adaptation to be successful, several physiological, neurological and biochemical mechanisms must take place behind the scenes. Let's have a closer look at how your eye actually operates in these conditions. Every eye absorbs photons via two kinds of cells: cones and rods, at the back of the eye; or, to be precise, on the retina. Together they make up the sensory layer that helps the eye pick up colors and light. These cells are found throughout your retina, except for in the small area opposite the pupil known as the fovea, where there are only cone cells. This section provides detailed sight, such as when reading. As you may know, the details and colors we see are sensed by cone cells, while the rods allow us to see black and white, and are light sensitive and detect movement.

This information is significant because, when you want to see something in the dark, like the edge of the last stair in a dark basement, it's more efficient to look at something right next to it. By looking to the side, you use the rods, which work better in the dark.

In addition to this, the pupils, the black circles in the middle of your eyes, dilate in the dark. It takes fewer than sixty seconds for your pupil to completely enlarge but dark adaptation continues to develop over approximately 30 minutes and, as you've experienced, during this time, your ability to see will increase greatly.

Here's an example of dark adaptation: when you first enter a dark cinema from a bright lobby and have a hard time finding a seat. But soon enough, you adapt to the situation and see better. This same thing occurs when you're looking at the stars in the sky. At first you probably won't be able to actually see that many. Keep looking; while you dark adapt, millions of stars will become easier to see. Despite the fact that you need several moments to adapt to the darker conditions, you'll always be able to re-adapt upon re-exposure to bright light, but then the dark adaptation process will have to begin from scratch if you go back into the dark.

This is why a lot people prefer not to drive when it's dark. If you look at the headlights of an approaching car, you may find yourself momentarily unable to see, until that car is gone and your eyes once again adjust to the night light. To prevent this, try not to look right at the car's lights, and learn to try to allow your peripheral vision to guide you.

There are several conditions that could potentially cause difficulty seeing at night, including: a nutritional deficiency, cataracts, glaucoma, or some other visual obstruction. Should you begin to detect problems with night vision, schedule an appointment with one of our eye care professionals who will be able to locate the source of the problem.