Sometimes you go to bed and turn off the light, but you just can't seem to doze off. You open your eyes and you can't see a thing. Your eyes normally require a few minutes to adjust to the dark and then the your surroundings come back into view. This is called ''dark adaptation''.
In order for night vision and dark adaptation to occur, several physiological, neurological and biochemical mechanisms must take place behind the scenes. So how does this work? The retina is a layer of cells at the back of the eye. The portion of the retina behind the pupil that is responsible for the point of focus is called the fovea. The retina comprises rod-shaped and cone-shaped cells. The rod cells are able to function even in low light conditions but those cells are not found in the fovea. What's the difference between rods and cones? Basically, details and colors we see are sensed by the cones, and the rods are sensitive to light.
Now that you know some background, let's relate it to dark adaptation. If you want to see something in the dark, like the edge of the last stair in a dark basement, instead of focusing right on it, try to look just beside it. When you do that, you use the part of the eye that has rods, which, as mentioned above, are more responsive to light, even if there isn't much of it.
Another way your eye responds to the dark is by your pupils dilating. It requires less than a minute for the pupil to completely dilate but your eyes will get better at seeing in the dark over a half hour period.
Here's an example of dark adaptation: if you leave a bright area and enter a dim one, for example, when coming inside after spending time in the sun. It takes a few noticeable moments until you begin to get used to normal indoor light. If you go back outside, those changes will vanish in a moment.
This is actually one reason behind why so many people prefer not to drive when it's dark. If you look right at the headlights of an oncoming car in traffic, you may find yourself momentarily unable to see, until that car passes and you readjust to the night light. A helpful way to avoid this is to avoid looking directly at the car's lights, and instead, use your peripheral vision to observe oncoming traffic at night.
There are several conditions that could contribute to decreased night vision, including: diet-related vitamin deficiencies, cataracts, glaucoma, or some other visual impediment. If you suspect difficulty with night vision, call to make an appointment with one of our eye doctors who will be able to identify and rectify it.