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A Closer Look at Night Vision

You wake suddenly, in the middle of the night, or maybe you're looking for the light switch or door in a dark room. It's happened to all of us. It takes a few minutes for your vision to return. This process, called ''dark adaptation,'' allows our vision to adjust to the 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, rod cells and cone cells, which are found on the retina at the back of the eye. Together they make up the sensory layer. This is the part that enables the eye to pick up colors and light. Cones and rods are distributed evenly throughout the retina, except for in the small area opposite the pupil known as the fovea. This contains only cone cells, and its main function involves creating a focused image. You may have heard that the cones contribute to color vision, while rod cells let us see black and white, and are light sensitive.

Now that you know some background, let's relate it to dark adaptation. If you want to see something in the dark, instead of focusing right on 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.

Your pupils also dilate in low light. The pupil grows to it its biggest capacity in less than a minute but it takes about 30-45 minutes for the eye to fully adapt and, as everyone has experienced, during this time, your ability to see in the low light setting will increase greatly.

Here's an example of dark adaptation: when you walk into a darkened cinema from a well-lit lobby and have a hard time finding somewhere to sit. After a while, you get used to the situation and before you know it, you can see. You'll experience the same thing when you're looking at stars at night. At first you probably won't be able to actually see that many. If you keep staring, your eyes will dark adapt and the stars will gradually appear. While it takes several moments to adapt to the darker conditions, you'll quickly be able to re-adapt upon re-exposure to bright light, but if you return to the darker setting, your eyes will need time to re-adjust again.

This explains one reason behind why so many people have trouble driving their cars at night. When you look right at the headlights of a car heading toward you, you may find yourself momentarily unable to see, until that car is gone and you once again adjust to the night light. To prevent this, don't look right at headlights, and instead, use peripheral vision in those situations.

If you're having trouble seeing when it's dark, book a consultation with our doctors who will make sure your prescription is up to date, and eliminate other and perhaps more severe causes for worsening vision, like cataracts and macular degeneration.

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