A Closer Look at Night Vision

Something wakes you up in the middle of the night, or maybe you're searching for a light switch or door handle or phone in a room with the lights off. It's happened to all of us. It takes a couple of minutes for your vision to return. This process is known as ''dark adaptation'' and it's what makes our eyes get used to the dark.

Many people don't know that night vision relies on several physical, neural and biochemical mechanisms. How does it actually happen? Firstly, let's examine the eye and its anatomy. Your eye has, in addition to other cells, 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 form the sensory layer that helps the eye detect light and color. The rod and cone cells are spread throughout the entire retina, except for in the small area known as the fovea, where there are only cone cells. This section is the part used for detailed sight, such as when reading. As you may know, the cones contribute to color vision, and the rods are sensitive to light.

How does this apply to dark adaptation? When you want to see something in the dark, instead of looking directly at it, try to use your peripheral vision. By looking to the side, you take advantage of the rods, which work better in the dark.

Another way your eye responds to the dark is by your pupils dilating. It takes less than a minute for your pupil to fully enlarge but dark adaptation will continue to develop for the next half hour. During this time, your eyes become 10,000 times more sensitive to light.

Dark adaptation occurs if you go from a very bright place to a dim one for example, when you go inside after spending time in the sun. While it takes a few noticeable moments to begin to see in the darker conditions, you will immediately be able to re-adapt upon returning to bright light, but if you return to the darker setting, your eyes will need time to adjust again.

This is actually one reason behind why a lot people have trouble driving their cars at night. When you look directly at the lights of a car heading toward you, you are momentarily blinded, until that car passes and your eyes readjust to the night light. To prevent this, try not to look right at the car's lights, and learn to try to allow peripheral vision to guide you.

There are numerous things that may cause inability to see at night, including: a nutritional deficiency, cataracts, glaucoma, or some other visual impediment. If you notice difficulty with night vision, call to make an appointment with one of our eye doctors who will be able to shed some light on why this is happening.