You're all ready for a good night's sleep, so you flick the light switch, but you just can't seem to doze off. You open your eyes and you can't see a thing. It takes a few minutes for your vision to return. This process, ''dark adaptation,'' causes our vision to see even when there's almost no light.
In order for night vision and dark adaptation to happen, several physiological, neurological and biochemical mechanisms have to take place behind the scenes. Let's have a closer look at how all this operates. Every eye features two kinds of cells: cones and rods, on the retina at the back of the eye. Together they form the sensory layer that helps the eye see light and color. The rod and cone cells exist throughout the retina, save for the small area opposite the pupil known as the fovea. The fovea is made up of only cone cells, and its primary function involves focusing on detail. As you may know, the cones help us perceive color and detail, while the rods are sensitive to light.
This information is significant because, when trying to find something in the dark, instead of focusing right on it, try to look just beside it. By looking to the side, you take advantage of the rods, which work better in the dark.
In addition to this, the pupils dilate in the dark. Your pupil grows to it its largest diameter in less than a minute but it takes approximately half an hour for the eye to fully adapt. During this time, sensitivity to light increases by a factor of 10,000 or more.
You'll experience dark adaptation when you walk into a darkened theatre from a well-lit lobby and struggle to find somewhere to sit. But soon enough, your eyes get used to the situation and before you know it, you can see. This same thing occurs when you're looking at the stars in the sky. Initially, you can't see very many. Keep looking; as you dark adapt, the stars will become brighter. Despite the fact that you need a few noticeable moments to begin to see in the dark, you'll always be able to re-adapt to exposure to bright light, but if you go back into the darker setting, your eyes will need time to adjust again.
This is actually why many people have difficulty driving at night. When you look directly at the headlights of an oncoming car in traffic, you are briefly unable to see, until you pass them and you readjust to the night light. A good way to avoid this is to avoid looking directly at headlights, and instead, use your peripheral vision to observe oncoming traffic at night.
There are a number of things that can cause decreased night vision, including: not getting enough Vitamin A in your diet, macular degeneration, cataracts, glaucoma, and others. Should you begin to suspect issues with night vision, call to make an appointment with one of our eye care professionals who will be able to locate the root of the problem.