Something wakes you up in the middle of the night, or perhaps you're searching for a light switch or door handle or phone in a dark room. It's happened to all of us. A number of minutes pass before you begin to recognize familiar things in your surroundings. This process, ''dark adaptation,'' causes us to adjust to the dark.
In order for night vision and dark adaptation to occur, many physiological, neurological and biochemical mechanisms have to take place behind the scenes. Let's have a closer look at how your eye actually operates in these conditions. The retina is a layer of cells at the back of the eye. The area of the retina directly behind the pupil that is responsible for the point of focus is called the fovea. The retina is made up of rod-shaped and cone-shaped cells. The rods are able to function even in low light conditions. They are absent from the fovea. As you may know, the cones contribute to color vision, and the rods help us visualize black and white, and are light sensitive and detect movement.
Considering these facts, if you want to see something in the dark, you'll be better off if you focus on the area off to the side of it. If, on the other hand, you focus on the object itself, you'll use the fovea, which is made up of cone cells that are less responsive in low light conditions.
Another part of the process is pupil dilation. It requires fewer than sixty seconds for the pupil to completely enlarge but it takes about 30-45 minutes for your eyes to achieve full light sensitivity and, as everyone has experienced, during this time, your ability to see despite the darkness will increase enormously.
Dark adaptation occurs when you go from a very bright place to a darker area for example, when coming inside after spending time in the sun. Even though your eyes require several moments to begin to see in the dark, you'll quickly be able to re-adapt upon your return 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 prefer not to drive at night. If you look at the ''brights'' of an oncoming vehicle, you are momentarily blinded, until you pass them and you readjust to the night light. To prevent this, try not to look directly at the car's lights, and learn to try to allow peripheral vision to guide you.
There are several things that could potentially cause difficulty seeing at night, including: diet-related vitamin deficiencies, cataracts, glaucoma, or some other visual obstruction. Should you begin to suspect that you have trouble in the dark, call to make an appointment with one of our eye doctors who will be able to shed some light on the issue.