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Our Amazing Ability to See in the Dark

Everyone has found themselves in a dark room, at one point or another, whether it be during childhood, due to a power outage, or just waking up in the middle of the night. After a while you are able to distinguish between the objects in the room and the darkness around you. We call this ”dark adaptation”.

In order for night vision and dark adaptation to occur, many physiological, neurological and biochemical mechanisms must take place behind the scenes. Let’s have a closer look at how all this operates. Your eye uses 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 enables the eye to pick up light and color. The rod and cone cells are distributed evenly throughout the retina, except for in the small area opposite the pupil known as the fovea, where there are only cone cells. That part is necessary for detailed sight, such as when reading. You might already be aware that the details and colors we see are detected by the cones, while rod cells allow us to see black and white, and are light sensitive.

Now that you know some background, let’s relate it to dark adaptation. If you’re looking at an object in the dark, like a faint star in a dark sky, instead of focusing right on it, try to look just beside it. That way, you’re avoiding the use of the fovea, which only has cells that are less sensitive to low light.

Your pupils also dilate in response to darkness. It takes approximately one minute for the pupil to completely enlarge but it takes about 30-45 minutes for your eyes to achieve full light sensitivity. During this time, your eyes become 10,000 times more sensitive to light.

Here’s an example of dark adaptation: when you enter a darkened theatre from a bright lobby and have a hard time locating a seat. But soon enough, your eyes adapt to the dark and see better. This same thing occurs when you’re looking at the stars in the sky. At the beginning, you probably won’t be able to actually see that many. If you keep gazing, your eyes will dark adapt and the stars will gradually appear. It’ll always take a few moments until you begin to get used to regular indoor light. Then if you walk back out outside, that dark adaptation will disappear in a moment.

This is actually one reason behind why so many people have trouble driving their cars at night. If you look right at the headlights of an approaching vehicle, you are momentarily unable to see, until you pass them and you once again adjust to the night light. A helpful way to avoid this is to avoid looking directly at headlights, and learn to try to allow peripheral vision to guide you.

If you’re struggling to see when it’s dark, call us to schedule an appointment with your eye care professional who will see if your prescription needs updating, and eliminate other and perhaps more serious reasons for poor night vision, like macular degeneration or cataracts.

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