Sometimes you get ready for bed and turn off the light, but you can't sleep. You open your eyes and find yourself enveloped in darkness. It takes a couple of minutes for your vision to return. We call this ''dark adaptation'' and it's what lets our eyes adjust to low light settings.
Many people don't know that night vision relies on several physical, neural and biochemical mechanisms. So how does it actually happen? Let's examine the eye and its complex anatomy. The retina is a layer of cells at the back of the eye. The area of the retina opposite the pupil which produces the point of focus is called the fovea. The retina comprises cone cells and rod cells, named for their respective shapes. The rod cells have the capacity to function more efficiently than cone cells in low light conditions. They are absent from the fovea. What's the difference between these two cell types? In short, cones help us see color and detail, while rod cells are sensitive to light and detect movement.
How does this apply to seeing in the dark? When you want to see something in the dark, like the edge of the last stair in a dark basement, it's more efficient to try to look at it with the side of your eye. 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.
Your pupils also dilate in response to darkness. The pupil reaches its biggest capacity in about a minute; however, your eyes will get better at seeing in the dark over a 30 minute time frame and, as you've experienced, during this time, your ability to see in the dark will increase remarkably.
Here's an example of dark adaptation: if you go from a very light-filled area to a dim one for instance, walking inside after being out in the sun. It takes a few noticeable moments until your eyes fully get used to regular indoor light. If you go back into the brightness, that dark adaptation will vanish in a moment.
This is actually why a lot people don't like to drive at night. If you look directly at the headlights of an oncoming car in traffic, you may find yourself briefly blinded, until that car passes and you once again adjust to the night light. A helpful way to prevent this sort of temporary blindness is to avoid looking directly at headlights, and learn to try to allow your peripheral vision to guide you.
There are a number of things that could be the cause of inability to see at night. These include a nutritional deficiency, macular degeneration, cataracts, glaucoma, and others. Should you begin to suspect issues with night vision, schedule an appointment with one of our eye care professionals who will be able to get to the root of the problem.