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Night Vision: How Does it Work?

It's happened to all of us: your house loses power 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 the your surroundings come back into view. This process, ''dark adaptation,'' causes our vision to see even when there's very little light.

A person with a healthy set of eyes probably takes night vision - and the biochemical, physical and neural mechanisms - for granted. Let's have a closer look at how all this operates. The retina is a layer of cells at the back of the eye. The area of the retina directly across from the pupil which produces sharp focused vision is called the fovea. The retina is made up of cone cells and rod cells, named for their respective shapes. The rod cells have the capacity to function even in low light conditions but those cells are absent from the fovea. You may have learned that the cones contribute to color vision, and rod cells let us see black and white, and are light sensitive and detect movement.

Let's put this all together. Imagine you want to see something in the dark, like the dresser in your darkened room, instead of looking directly at it, try to use your peripheral vision. 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.

Furthermore, the pupils dilate in response to darkness. It takes fewer than sixty seconds for the pupil to completely enlarge; however, it takes about half an hour for you to fully adapt. During this time, your eyes become 10,000 times more sensitive to light.

You'll experience dark adaptation when you go from a very light-filled place to a dim one for instance, when coming inside after sitting in the sun. Even though it takes 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 one reason behind why so many people don't like to drive at night. When you look at the lights of opposing traffic, you may find yourself momentarily unable to see, until that car is gone and your eyes readjust to the night light. To prevent this, try not to look directly at headlights, and learn to use peripheral vision to observe oncoming traffic at night.

There are numerous things that could be the cause of decreased night vision. These include diet-related vitamin deficiencies, macular degeneration, cataracts, glaucoma, and others. Should you begin to suspect that you have problems with seeing at night, schedule an appointment with one of our eye care professionals who will be able to shed some light on why this is happening.