Everyone's found themselves in a dark room, at one time or another. You notice that it is almost impossible to see for several moments before your eyes adjust. We call this ''dark adaptation'' and it's what lets our eyes see in the dark.
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 does this work? The retina is a layer of cells at the back of the eye. The section of the retina directly opposite the pupil which produces the point of focus is called the fovea. The retina comprises rod-shaped and cone-shaped cells. The rod cells are able to function more efficiently than cone cells in low light conditions. Those cells are not found in the fovea. As you may know, the details and colors we see are sensed by the cones, and the rods allow us to see black and white, and are light sensitive.
This information is significant because, when you're trying to find something in the dark, like the dresser in your darkened room, it's much more efficient to 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.
The pupils also dilate in response to darkness. Your pupil reaches its largest diameter in less than a minute; however, dark adaptation keeps enhacing your vision over approximately 30 minutes and, as everyone has experienced, during this time, your ability to see in the low light setting will increase enormously.
Here's an example of dark adaptation: when you enter a dark movie theatre from a well-lit lobby and struggle to find a seat. But soon enough, your eyes get used to the dark and see better. You'll experience the same thing when you're looking at the stars in the sky. At the beginning, you can't see very many. Keep looking; as your eyes continue to dark adapt, millions of stars will gradually appear. Despite the fact that your eyes require several moments to begin to see in the darker conditions, you'll quickly be able to re-adapt to exposure to bright light, and this resets any dark adaptation that had developed where it was darker.
This is actually why so many people prefer not to drive at night. If you look at the headlights of opposing traffic, you may find yourself briefly blinded, until that car is gone and you once again adjust to the night light. To prevent this, try not to look directly at headlights, and learn to use peripheral vision in those situations.
There are numerous conditions that could, hypothetically lead to difficulty seeing at night. Here are some possibilities: not getting enough Vitamin A in your diet, cataracts, glaucoma, or some other visual interference. If you detect issues with night vision, schedule an appointment with one of our eye care professionals who will be able to get to the root of the problem.