You wake suddenly, in the middle of the night, or you’re searching for a light switch or door handle or phone in the dark. It’s happened to all of us. Gradually, the things in the room begin take shape. This process, called ”dark adaptation,” causes people to see even when it’s really dark.
In order for night vision and dark adaptation to occur, several physiological, neurological and biochemical mechanisms must take place behind the scenes. Let’s talk about how this works. 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 sharp focused vision is called the fovea. The retina comprises rod-shaped and cone-shaped cells. The rod cells are able to function better than cone cells 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, and rod cells allow us to see black and white, and are light sensitive and detect movement.
Now that you know some background, let’s relate it to dark adaptation. If you want to see something in the dark, like the dresser in a darkened room, it’s much better to view it through the side of your eye. When you do that, you use the part of the eye that has rods, which, as mentioned above, are more responsive to light, even if there isn’t much of it.
In addition to this, the pupils, the black circles in the middle of your eyes, dilate in low light. It requires fewer than sixty seconds for the pupil to fully dilate; however, it takes about 30-45 minutes for you to achieve full light sensitivity and, as you’ve experienced, during this time, your ability to see despite the darkness will increase greatly.
Here’s an example of dark adaptation: when you enter a dark movie theatre from a well-lit area and struggle to find a seat. After a while, your eyes adapt to the situation and before you know it, you can see. You’ll experience the same thing when you’re looking at stars at night. At the beginning, you can’t see very many. If you keep gazing, your eyes will dark adapt and the stars will become visible. Despite the fact that you need several moments to get used to the dark, you’ll quickly be able to re-adapt upon your return to bright light, and this resets any dark adaptation that had developed where it was darker.
This explains why many people don’t like to drive at night. When you look at the headlights of an oncoming car in traffic, you are briefly unable to see, until that car is gone and you readjust to the night light. To prevent this, try not to look directly at the car’s lights, and instead, use your peripheral vision to observe oncoming traffic at night.
If you’re struggling to see at night or in the dark, book a consultation with our doctors who will make sure your prescription is up to date, and eliminate other reasons for worsened vision, such as cataracts and macular degeneration.