Everyone’s found themselves in the dark, at some point in their lives. Your eyes normally require a few minutes to adjust to the dark and then you can see again. We call this ”dark adaptation”.
Night vision requires 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 absorbs photons via two kinds of cells: cones and rods, on the retina at the back of the eye. Together they make up the sensory layer that gives your eye the ability to detect light and color. These cells exist throughout your retina, with the exception of the small area opposite the pupil known as the fovea. This contains 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, and rod cells are sensitive to light and detect movement.
Now that you know some background, let’s relate it to dark adaptation. If you want to see something in the dark, like a small star in the night sky, it’s more efficient to view it with your peripheral vision. That way, you’re avoiding the use of the fovea, which only has cells that are less sensitive to low light.
In addition to this, the pupils, the black circles in the middle of your eyes, dilate in low light. Your pupil dilates to its biggest capacity in less than a minute but it takes about 30-45 minutes for your eyes to achieve full light sensitivity. During this time, your eyes become 10,000 times more sensitive to light.
Here’s an example of dark adaptation: when you go from a very bright area to a darker one for instance, when coming inside after spending time in the sun. It’ll always take a few moments until your eyes fully get used to regular indoor light, but if you walk back out into the brightness, that dark adaptation will vanish in a flash.
This explains one reason behind why many people prefer not to drive at night. If you look directly at the lights of a car heading toward you, you may find yourself momentarily blinded, until you pass them and your eyes once again adjust to the night light. A good way to avoid this is to avoid looking directly at the car’s lights, and learn to use your peripheral vision to observe oncoming traffic at night.
There are a number of things that could be the cause of difficulty seeing in the dark. These include a nutritional deficiency, macular degeneration, cataracts, glaucoma, and others. If you detect issues with night vision, call to make an appointment with one of our eye care professionals who will be able to locate the source of the problem.