Something wakes you up in the middle of the night, or maybe you’re searching for a light switch or door handle or phone in the dark. It’s happened to all of us. At first you can’t see, but gradually the things in the room begin take shape. This process, called ”dark adaptation,” allows people to see even when there’s almost no light.
In order for night vision and dark adaptation to happen, many physiological, neurological and biochemical mechanisms must take place behind the scenes. So how do our eyes actually function in the dark? Let’s begin by having a closer look at some eye anatomy. Your eye features rod cells and cone cells, which are found on the retina at the back of the eye. Together they make up the sensory layer. This is the part that enables the eye to detect colors and light. These cells exist throughout the entire retina, with the exception of the small area opposite the pupil known as the fovea. It has only cone cells, and its primary function involves focusing on detail. What’s the difference between rods and cones? Basically, details and colors we see are sensed by the cones, and rod cells are sensitive to light and detect movement.
How does this apply to dark adaptation? When you want to see something in the dark, like the dresser in a darkened room, it’s better to look at the area off to the side of it. You want to maximize the use of the rod cells in low light, and avoid relying on your cone-rich fovea, even though it seems counter-intuitive to look away from the object you want to see.
Another process your eye undergoes is pupil dilation. It takes less than a minute for your pupil to fully enlarge but it takes approximately 30 minutes for you to achieve full light sensitivity. During this time, it is estimated that your ability to see can increase by a factor of 10,000 or more.
You’ll experience dark adaptation if you exit a bright area and enter a dim one, for instance, when coming inside after sitting in the sun. It’ll always require a few moments until you begin to adapt to normal indoor light. Then if you walk back out into the brightness, that dark adaptation will be lost in the blink of an eye.
This explains one reason behind why a lot people don’t like to drive at night. If you look right at the ”brights” of an approaching car, you are momentarily blinded, until that car is gone and you readjust to the night light. To prevent this, try not to look right at the car’s lights, and learn to try to allow peripheral vision to guide you.
If you’re finding it challenging to see when it’s dark, schedule a consultation with our doctors who will be able to shed some light on why this is occurring, and eliminate other reasons for worsened vision, such as macular degeneration or cataracts.