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 dark room. It's happened to all of us. You notice that it's difficult to see for a few moments and then the room becomes visible again. We call this ''dark adaptation''.
A person with a healthy set of eyes probably takes night vision - and the role of the biochemical, physical and neural mechanisms - for granted. Let's have a look at how all this operates. Every eye has, in addition to other cells, two kinds of cells: cones and rods, at the back of the eye; or, to be precise, on the retina. Together they form the sensory layer. This is the part that enables the eye to pick up colors and light. Cones and rods are spread throughout the entire retina, save for the small area called the fovea. This has only cone cells, and its primary function involves creating a focused image. As you may know, the details and colors we see are sensed by the cones, while rod cells help us visualize black and white, and are light sensitive and detect movement.
Now that you know some background, let's relate it to dark adaptation. If looking at an object in the dark, instead of focusing right on 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 requires fewer than sixty seconds for the pupil to completely dilate but it takes approximately 30-45 minutes for you to achieve full light sensitivity.
You'll experience dark adaptation when you walk into a dark cinema from a bright area and have a hard time finding a seat. But soon enough, your eyes get used to the situation and see better. You'll experience the same thing when you're looking at the stars in the sky. At the beginning, you won't see many. Keep looking; as your eyes continue to dark adapt, millions of stars will become easier to see. It'll always take a few moments for your eyes to adapt to regular indoor light. If you go back into the brightness, those changes will be lost in the blink of an eye.
This explains why a lot people have difficulty driving at night. If you look right at the ''brights'' of an approaching vehicle, you are momentarily blinded, until you pass them and you readjust to the night light. To prevent this, try not to look right at headlights, and instead, use your peripheral vision to observe oncoming traffic at night.
There are several things that could contribute to difficulty seeing in the dark. These include not getting enough Vitamin A in your diet, macular degeneration, cataracts, glaucoma, and others. Should you begin to suspect that you experience problems with seeing at night, book an appointment with one of our eye care professionals who will be able to get to the source of the problem.