It's happened to all of us: there's a blackout and you need to locate a flashlight or the fuse box. You notice that it's difficult to see for a couple of moments before the room becomes visible again. This process is known as ''dark adaptation''.
Night vision requires a number of biochemical, physical and neural mechanisms - for granted. How do our eyes operate in low light? Let's begin by having a closer look at some eye anatomy. 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 form the sensory layer that helps the eye pick up colors and light. The rod and cone cells are spread throughout your retina, except for in the small area known as the fovea, where there are only cone cells. This section is necessary for detailed vision, for example when reading. As you may know, the cones enable us to perceive color and detail, while 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, you'll be better off if you try to look at it with your peripheral vision. It works by taking advantage of the light-sensitive rod cells.
Another method by which your eye responds to the dark is by your pupils dilating. The pupil dilates to its biggest capacity within a minute; however, dark adaptation will continue to develop for the next half hour.
Here's an example of dark adaptation: when you first enter a dark cinema from a bright lobby and have a hard time locating a seat. After a while, your eyes get used to the dark and before you know it, you can see. This same thing occurs when you're looking at stars at night. At first you probably won't be able to actually see that many. Keep looking; as your eyes continue to dark adapt, millions of stars will become easier to see. Even though it takes several moments to adapt to the darker conditions, you'll quickly be able to re-adapt upon your return to bright light, but then the dark adaptation process will have to begin from scratch if you go back into the dark.
This explains one reason behind why so many people don't like to drive when it's dark. When you look at the lights of an approaching vehicle, you may find yourself momentarily unable to see, until that car is gone and you once again adjust to the night light. A helpful way to prevent this sort of temporary blindness is to avoid looking right at the car's lights, and learn to try to allow peripheral vision to guide you.
There are several things that could be the cause of difficulty seeing in the dark. Here are some possibilities: a nutritional deficiency, macular degeneration, cataracts, glaucoma, and others. If you notice that you experience trouble in the dark, schedule an appointment with one of our eye care professionals who will be able to get to the source of the problem.