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Night Vision

You wake suddenly, in the middle of the night, or perhaps you're trying to find the light switch or door in a room with the lights off. These sorts of things happen to us all the time. It takes a few minutes for your eyes to adjust to the dark. We call this ''dark adaptation''.

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 this works. Your eye takes in various forms of light using rod cells and cone cells, on the retina at the back of the eye. Together they make up the sensory layer that gives your eye the ability to see colors and light. The rod and cone cells are found throughout the entire retina, with the exception of the small area opposite the pupil known as the fovea. It has only cone cells, and its primary function involves creating a focused image. You may have heard that the details and colors we see are sensed by the cones, while the rods allow us to see black and white, and are light sensitive.

How does this apply to seeing in the dark? When you're trying to find something in the dark, like the edge of the last stair in a dark basement, instead of looking directly at 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.

Another process your eye undergoes is pupil dilation. It takes less than a minute for the pupil to completely dilate but your eyes will keep adapting over a 30 minute time frame.

Here's an example of dark adaptation: when you first enter a dark cinema from a bright lobby and have a hard time finding somewhere to sit. After a while, your eyes adapt to the dark and see better. This same thing occurs when you're looking at stars at night. At the beginning, you probably won't be able to actually see that many. If you keep looking, your eyes will dark adapt and millions of stars will become brighter. It'll always require a few moments until you begin to adjust to regular indoor light. If you go back into the brightness, those changes will vanish in the blink of an eye.

This is actually one reason behind why many people prefer not to drive when it's dark. If you look at the headlights of an oncoming car in traffic, you may find yourself briefly blinded, until that car is gone and your eyes once again adjust to the night light. To prevent this, try not to look directly at headlights, and learn to try to allow your peripheral vision to guide you.

If you're having trouble seeing when it's dark, schedule a consultation with our doctors who will be able to look into why this is occurring, and rule out other and perhaps more serious reasons for poor night vision, like cataracts and macular degeneration.

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