Everyone has found themselves in a dark room, at one point or another, whether it be during childhood, due to a power outage, or just waking up in the middle of the night. After a few moments you can see again. This process, ''dark adaptation,'' causes our vision to see even when there's very little light.
Many people don't know that night vision is dependent upon the cooperation of physical, neural and biochemical mechanisms. Let's have a look at how this works. The retina is a layer of cells at the back of the eye. The section of the retina directly across from the pupil which produces the point of focus is called the fovea. The retina comprises rod-shaped and cone-shaped cells. The rod cells have the capacity to function more efficiently than cone cells in low light conditions. They are not found in the fovea. What's the difference between rods and cones? In short, details and colors we see are sensed by cone cells, while rod cells let us see black and white, and are light sensitive.
Let's put this all together. Imagine 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 use your peripheral vision. 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.
The pupils also dilate in the dark. The pupil reaches its biggest capacity in about a minute but it takes approximately 30 minutes for your vision to fully adapt.
Dark adaptation occurs when you enter a dark theatre from a bright lobby and have trouble finding a seat. After a while, you adapt to the dark and see better. You'll experience a very similar phenomenon when you're looking at stars at night. At the beginning, you won't see many. As you keep looking, your eyes will dark adapt and the stars will become visible. Even though you need a few noticeable moments to get used to the darker conditions, you'll always be able to re-adapt upon re-exposure to bright light, but then the dark adaptation process will have to begin from scratch if you go back into the dark.
This is actually one reason behind why many people have trouble driving their cars at night. When you look right at the headlights of a car heading toward you, you are briefly unable to see, until that car passes and your eyes once again adjust to the night light. To prevent this, don't look right at the car's lights, and learn to try to allow your peripheral vision to guide you.
There are numerous conditions that could potentially cause trouble with night vision. Here are some possibilities: a nutritional deficiency, macular degeneration, cataracts, glaucoma, and others. Should you begin to suspect that you experience trouble in the dark, book an appointment with one of our eye care professionals who will be able to identify and rectify it.