You wake from a dream in the middle of the night, or maybe you’re looking for a light switch or door handle or phone in a dark room. We’ve all found ourselves in the dark before. You need several moments to get used to the dark and then you are able to see better. This process, ”dark adaptation,” allows our vision to see even when there’s very little light.
In order for night vision and dark adaptation to be successful, many physiological, neurological and biochemical mechanisms have to take place behind the scenes. Let’s have a look at how all this operates. Your eye features 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 enables the eye to see colors and light. The rod and cone cells exist throughout your entire retina, except for in the small area called the fovea. The fovea has only cone cells, and its main function involves focusing on detail. What’s the functional difference between these two cell types? Basically, cones contribute to color vision, while rod cells are sensitive to light and detect movement.
So, if struggling to view something in the dark, like a dim star in the night sky, it’s better to focus on something off to the side of it. By looking to the side, you take advantage of the rods, which work better in the dark.
Another process your eye undergoes is pupil dilation. The pupil dilates to its largest diameter in about a minute; however, it takes approximately 30-45 minutes for your eyes to fully adapt. During this time, your eyes become 10,000 times more sensitive to light.
Here’s an example of dark adaptation: when you enter a darkened theatre from a well-lit lobby and have a hard time locating somewhere to sit. But after a few minutes, your eyes get used to the situation and see better. You’ll experience a very similar phenomenon when you’re looking at the stars in the sky. At the beginning, you won’t see many. Keep looking; as your eyes continue to dark adapt, millions of stars will gradually appear. Even though you need a few noticeable moments to get used to the darker conditions, you will immediately be able to re-adapt to exposure to bright light, but if you go back into the darker setting, your eyes will need time to re-adjust again.
This is why many people don’t like to drive at night. When you look right at the ”brights” of an oncoming vehicle, you are momentarily blinded, until that car is gone and your eyes readjust to the night light. To prevent this, try not to look directly at the car’s lights, and instead, try to allow peripheral vision to guide you.
There are numerous conditions that could be the cause of decreased night vision. Here are some possibilities: diet-related vitamin deficiencies, macular degeneration, cataracts, glaucoma, and others. If you notice problems with night vision, call to make an appointment with one of our eye doctors who will be able to shed some light on why this is happening.