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Night Vision: How Does it Work?

You wake suddenly, in the middle of the night, or you're searching for a light switch or door handle or phone in a dark room. It's happened to all of us. Your eyes normally require a few minutes to adjust to the dark and then the your surroundings come back into view. This process, called ''dark adaptation,'' allows us to see even when there's very little light.

In order for night vision and dark adaptation to happen, many physiological, neurological and biochemical mechanisms have to take place behind the scenes. But how does this work? The human eye takes in various forms of light using two kinds of cells: cones and rods, which are found at the back of the eye; or, to be precise, on the retina. Together they make up the sensory layer. This is the part that gives your eye the ability to pick up colors and light. Cones and rods are spread throughout the entire retina, with the exception of the small area opposite the pupil known as the fovea. The fovea is made up of only cone cells, and its main function involves focusing. As you may know, the cones enable us to perceive color and detail, while rod cells are sensitive to light.

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 small star in a dark sky, instead of looking directly at it, try to use your peripheral vision. That way, you're avoiding the use of the fovea, which only has cells that are less sensitive to low light.

Another mechanism your eye uses in low light is pupil dilation. It takes fewer than sixty seconds for your pupil to completely enlarge; however, it takes about 30-45 minutes for your eyes to achieve full light sensitivity.

You'll experience dark adaptation if you leave a bright area and enter a dim one, for example, when you go inside after being out in the sun. It'll always take a few moments for your eyes to adjust to regular indoor light. Then if you walk back out outside, those changes will disappear in a moment.

This is actually why a lot people have difficulty driving at night. When you look directly at the lights of a car heading toward you, you are momentarily unable to see, until that car is gone and your eyes readjust to the night light. A good way to avoid this is to avoid looking right at the car's lights, and instead, 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 our doctors who will be able to shed some light on why this is happening, and eliminate other reasons for decreased vision, such as macular degeneration or cataracts.

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