Something wakes you up in the middle of the night, or perhaps you're trying to find the light switch or door in a room with the lights off. It's happened to all of us. You notice that it is difficult to see anything for several moments before your eyes adjust. This process, ''dark adaptation,'' allows our eyes to adjust to the dark.
Many people don't know that night vision is dependent upon several physical, neural and biochemical mechanisms. Let's have a closer look at how this works. The human eye contains photoreceptors that can be classified as two kinds of cells: cones and rods, at the back of the eye; or, to be precise, on the retina. Together they make up the sensory layer that helps the eye see colors and light. Cones and rods are found throughout the entire retina, with the exception of the small area opposite the pupil known as the fovea, where there are only cone cells. The fovea provides detailed vision, such as when reading. What's the functional difference between these two cell types? Basically, details and colors we see are detected by the cones, and the rods are sensitive to light and detect movement.
How does this apply to being able to see in the middle of the night? When you're attempting to make out an object in the dark, like a dim star in a dark sky, you'll be better off if you focus on 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.
The pupils also dilate in response to darkness. It takes fewer than sixty seconds for the pupil to completely enlarge; however, your eyes will get better at seeing in the dark over a 30 minute period and, as you've experienced, during this time, your ability to see will increase greatly.
You'll experience dark adaptation when you leave a bright area and enter a dim one, for instance, when coming inside after sitting in the sun. It'll always take a few moments until you begin to get used to normal indoor light, but if you walk back out into the brightness, that dark adaptation will disappear in a flash.
This explains why so many people don't like to drive at night. If you look directly at the lights of opposing traffic, you are momentarily blinded, until that car passes and your eyes readjust to the night light. A helpful way to avoid this is to avoid looking right at headlights, and instead, use peripheral vision to observe oncoming traffic at night.
If you're struggling to see at night or in the dark, call us to schedule a consultation with our doctors who will see if your prescription needs updating, and eliminate other reasons for worsened vision, such as macular degeneration or cataracts.