You wake suddenly, in the middle of the night, or maybe you’re trying to find the light switch or door in the dark. These sorts of things happen to us all the time. You notice that it’s almost impossible to see for a couple of moments and then the room becomes visible again. This process, “dark adaptation,” causes our eyes to see even when it’s really dark.
Night vision involves a number of biochemical, physical and neural mechanisms – for granted. Let’s have a closer look at how your eye actually operates in these conditions. The human eye takes in various forms of light using rod cells and cone cells, 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 helps the eye detect colors and light. Cones and rods are found throughout the entire retina, with the exception of the small area known as the fovea. It is made up of only cone cells, and its main function involves focusing. You may have learned that the cones contribute to color vision, while rod cells help us visualize black and white, and are light sensitive and detect movement.
Considering these facts, if you want to see something in the dark, like the dresser in a darkened room, it’s better to focus on the area next to it. If, on the other hand, you focus on the object itself, you’ll use the fovea, which is made up of cone cells that are less responsive in low light conditions.
Another process your eye undergoes is pupil dilation. The pupil reaches its largest diameter in about a minute but dark adaptation keeps improving your ability to see for the next half hour. During this time, your eyes become 10,000 times more sensitive to light.
You’ll experience dark adaptation when you exit a bright area and enter a dim one, for example, when coming inside after being out in the sun. While it takes a few noticeable moments to get used to the darker conditions, you’ll always be able to re-adapt to exposure to bright light, but then the dark adaptation process will have to begin from scratch if you go back into the dark.
This explains why many people don’t like to drive at night. When you look directly at the headlights of opposing traffic, you may find yourself briefly unable to see, until you pass them and your eyes once again adjust to the night light. A helpful way to avoid this is to avoid looking directly at headlights, and learn to use peripheral vision in those situations.
If you’re having trouble seeing when it’s dark, book an appointment with our doctors who will confirm that your prescription is up to date, and eliminate other reasons for decreased vision, such as macular degeneration or cataracts.
Originally posted 2017-05-03 09:29:25.