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In the Middle of the Night: Seeing in the Dark

It's happened to all of us: there's a blackout and you've got to find a flashlight or the fuse box. At first you can't see, but gradually the things in the room begin become visible. This process, called ''dark adaptation,'' causes people to adjust to the dark.

In order for night vision and dark adaptation to happen, several physiological, neurological and biochemical mechanisms must take place behind the scenes. So how does it really work? Let's examine the eye and its complex anatomy. Every eye features two kinds of cells: cones and rods, which are found on the retina at the back of the eye. Together they make up the sensory layer. This is the part that gives your eye the ability to detect light and color. Cones and rods are found throughout your retina, with the exception of the small area called the fovea, where there are only cone cells. The fovea is necessary for detailed vision, for example when reading. You may have learned 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 attempting to make out an object in the dark, like a distant star in the night sky, it's more efficient to try to look at it through your peripheral vision. It works by taking advantage of the light-sensitive rod cells.

In addition to this, the pupils, the black circles in the middle of your eyes, dilate in low light. The pupil reaches its maximum size within 60 seconds; however, dark adaptation continues to develop over approximately 30 minutes.

Here's an example of dark adaptation: when you walk into a darkened cinema from a well-lit lobby and struggle to find somewhere to sit. After a while, you get used 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. As you keep gazing, your eyes will dark adapt and millions of stars will gradually appear. It takes a few noticeable moments until you begin to get used to normal indoor light. If you go back outside, those changes will be lost in a flash.

This is one reason behind why a lot people have difficulty driving at night. When you look directly at the lights of an oncoming car in traffic, you are momentarily blinded, until that car passes and your eyes readjust to the night light. To prevent this, don't look right at the car's lights, and instead, use your peripheral vision in those situations.

There are several conditions that may cause difficulty seeing in the dark. Here are some possibilities: a nutritional deficiency, macular degeneration, cataracts, glaucoma, and others. If you suspect that you experience difficulty seeing in the dark, schedule an appointment with one of our eye doctors who will be able to locate the root of the problem.

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