Everyone's found themselves in the dark, at some point in their lives. After a while you begin to recognize familiar things in your surroundings. This is called ''dark adaptation''.
In order for night vision and dark adaptation to occur, several physiological, neurological and biochemical mechanisms have to take place behind the scenes. So how do our eyes actually function in low light? Let's examine some eye anatomy. The retina is a layer of cells at the back of the eye. The section of the retina opposite the pupil which produces the point of focus is called the fovea. The retina comprises cone cells and rod cells, named for their respective shapes. The rods have the capacity to function better than cone cells in low light conditions. They are not found in the fovea. As you may know, the cones help us see color and detail, and rod cells let us see black and white, and are light sensitive.
Considering these facts, if looking at an object in the dark, like the edge of the last stair in a dark basement, you'll be better off if you look at the area right next to it. 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. It requires approximately one minute for your pupil to completely dilate; however, dark adaptation will continue to increase for the next half hour.
Dark adaptation occurs when you first enter a darkened theatre from a bright lobby and have a hard time locating somewhere to sit. But after a couple of minutes, you adapt to the dark and see better. This same thing occurs when you're looking at stars at night. At the beginning, you can't see very many. If you keep staring, your eyes will dark adapt and millions of stars will gradually appear. Even though your eyes require several moments to begin to see in the darker conditions, you'll always be able to re-adapt to exposure to bright light, but if you return to the darker setting, your eyes will need time to adjust again.
This is one reason behind why so many people have trouble driving their cars at night. When you look directly at the ''brights'' of a car heading toward you, you are briefly blinded, until you pass them and your eyes once again adjust to the night light. To prevent this, try not to look directly at headlights, and learn to use your peripheral vision in those situations.
There are a number of conditions that could potentially lead to trouble seeing at night. Here are some possibilities: not getting enough Vitamin A in your diet, macular degeneration, cataracts, glaucoma, and others. Should you begin to detect issues with night vision, schedule an appointment with one of our eye care professionals who will be able to identify and rectify it.