Everyone's found themselves in a dark room, at some point in their lives. Your eyes normally require a few minutes to adjust to the dark and then the your surroundings come back into view. This process, ''dark adaptation,'' allows us to see even when it's really dark.
A person with a healthy set of eyes probably takes night vision - and the biochemical, physical and neural mechanisms - for granted. Let's have a closer look at how all this operates. 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 comprises cone cells and rod cells, named for their respective shapes. The rod cells are able to function even in low light conditions but they are not found in the fovea. You might already know that 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 and detect movement.
How does this apply to seeing in the dark? When you want to see something in the dark, like the dresser in your darkened room, instead of looking directly at it, try to look just beside 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 method by which your eye responds to darkness is by your pupils dilating. It requires approximately one minute for your pupil to fully enlarge but it takes about half an hour for you to achieve full light sensitivity and, as you've experienced, during this time, your ability to see in the dark will increase remarkably.
Dark adaptation occurs when you enter a dark cinema from a bright lobby and struggle to find somewhere to sit. After a while, you get used to the dark and see better. This same thing occurs when you're looking at stars at night. Initially, you probably won't be able to actually see that many. As you keep staring, your eyes will dark adapt and millions of stars will gradually appear. It'll always require a few moments until your eyes fully adjust to normal indoor light. If you walk back out outside, those changes will vanish in a moment.
This is one reason behind why so many people don't like to drive at night. When you look directly at the ''brights'' of an approaching car, you may find yourself briefly unable to see, until that car passes and you once again adjust to the night light. To prevent this, don't look right at headlights, and instead, try to allow your peripheral vision to guide you.
There are numerous conditions that can cause difficulty seeing in the dark. These include a nutritional deficiency, macular degeneration, cataracts, glaucoma, and others. Should you begin to suspect that you experience problems with dark adapting, book an appointment with one of our eye doctors who will be able to shed some light on why this is happening.