Sometimes you get ready for bed and turn off the light, but you just can't seem to doze off. You open your eyes and you can't see anything. At first you can't see, but gradually the things in the room begin become visible. This is called ''dark adaptation'' and it's what lets our eyes get used to the dark.
Many people don't know that night vision is dependent upon the cooperation of physical, neural and biochemical mechanisms. How does it actually work? Firstly, let's examine some eye anatomy. The retina is a layer of cells at the back of the eye. The portion of the retina directly across from the pupil which produces the point of focus is called the fovea. The retina is made up of cone cells and rod cells, named for their respective shapes. The rods have the capacity to function even in low light conditions. Those cells are not found in the fovea. What's the functional difference between these two cell types? Basically, details and colors we see are detected by the cones, while the rods let us see black and white, and are light sensitive.
Now that you know some background, let's relate it to dark adaptation. If you want to see something in the dark, instead of looking right at it, try to look just beside it. It works by implementing the light-sensitive rod cells.
Another mechanism your eye employs in low light is pupil dilation. It takes fewer than sixty seconds for the pupil to completely dilate but it takes approximately 30 minutes for your vision to fully adapt and, as everyone has experienced, during this time, your ability to see despite the darkness will increase enormously.
Dark adaptation occurs when you first enter a dark theatre from a well-lit lobby and have a hard time finding somewhere to sit. After a while, your eyes adapt to the dark and before you know it, you can see. This same thing occurs when you're looking at stars at night. Initially, you probably won't be able to actually see that many. If you keep looking, your eyes will dark adapt and the stars will become easier to see. It'll always take a few moments until you begin to adapt to normal indoor light. If you walk back out outside, those changes will vanish in a flash.
This is one reason behind why a lot people don't like to drive when it's dark. When you look at the headlights of an approaching car, you are momentarily blinded, until that car passes and you readjust to the night light. To prevent this, don't look right at the car's lights, and learn to try to allow peripheral vision to guide you.
There are a number of conditions that may cause inability to see at night, including: diet-related vitamin deficiencies, macular degeneration, cataracts, glaucoma, and others. If you detect problems with night vision, book an appointment with one of our eye care professionals who will be able to get to the source of the problem.