You wake from a dream in the middle of the night, or you're looking for a light switch or door handle or phone in a dark room. It's happened to all of us. A number of minutes pass before you can see again. This process, called ''dark adaptation,'' causes people to adjust to the dark.
In order for night vision and dark adaptation to work, many physiological, neurological and biochemical mechanisms have to take place behind the scenes. So how does it actually happen? Firstly, let's examine the eye and its anatomy. The human eye takes in various forms of light using two kinds of cells: cones and rods, which are found on the retina at the back of the eye. Together they form the sensory layer that gives your eye the ability to pick up light and color. The rod and cone cells are distributed evenly throughout your retina, except for in the small area called the fovea, where there are only cone cells. This section is the part used for detailed vision, for example when reading. What's the functional difference between these two cell types? In short, details and colors we see are detected by cone cells, 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 the edge of the last stair in a dark basement, 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.
The pupils also dilate in response to darkness. Your pupil dilates to its biggest capacity within 60 seconds but it takes approximately 30 minutes for your eyes to achieve full light sensitivity.
You'll experience dark adaptation when you exit a bright area and enter a dim one, for example, when you go inside after being out in the sun. Despite the fact that you need a few noticeable moments to get used to the dark, you will immediately be able to re-adapt to exposure to bright light, but if you return to the darker setting, your eyes will need time to re-adjust again.
This is actually why a lot people prefer not to drive when it's dark. When you look directly at the lights of an oncoming car, you are momentarily blinded, until that car is gone and you readjust to the night light. A helpful way to prevent this sort of temporary blindness is to avoid looking right at headlights, and instead, try to allow your peripheral vision to guide you.
If you're struggling to see at night or in the dark, book a consultation with our doctors who will see if your prescription needs updating, and rule out other reasons for decreased vision, such as cataracts and macular degeneration.