Imagine your house loses power and you need to locate a flashlight or the fuse box. At first you can't see, but gradually the things in the room begin take shape. This process, called ''dark adaptation,'' causes our vision to see even when it's really dark.
A person with a healthy set of eyes probably takes night vision – and the role of the biochemical, physical and neural mechanisms – for granted. 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 opposite the pupil which produces sharp focused vision is called the fovea. The retina is made up of rod-shaped and cone-shaped cells. The rod cells are able to function even in low light conditions. Those cells are not found in the fovea. What's the difference between rods and cones? Basically, cones help us perceive color and detail, and the rods help us visualize black and white, and are light sensitive.
Let's put this all together. Imagine you want to see something in the dark, like a small star in a dark sky, instead of looking directly at 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 low light. It requires approximately one minute for the pupil to fully enlarge; however, it takes about 30 minutes for you to fully adapt and, as everyone has experienced, during this time, your ability to see in the dark will increase remarkably.
Dark adaptation occurs if you go from a very light-filled place to a darker area for instance, when you go inside after sitting in the sun. While it takes several moments to get used to 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 don't like to drive at night. If you look directly at the headlights of an approaching vehicle, you may find yourself momentarily blinded, until you pass them and your eyes readjust to the night light. A good way to avoid this is to avoid looking right at headlights, and learn to try to allow your peripheral vision to guide you.
There are a number of things that could, hypothetically lead to trouble seeing at night. Here are some possibilities: not getting enough Vitamin A in your diet, cataracts, glaucoma, or some other visual obstruction. Should you begin to suspect difficulty with night vision, book an appointment with one of our eye doctors who will be able to locate the root of the problem.