Let's say your house loses power and you need to locate a flashlight or the fuse box. A number of minutes pass before you begin to recognize familiar things in your surroundings. This is called "dark adaptation" and it makes our eyes adjust to low light settings.
Many people don't know that night vision is dependent upon the cooperation of physical, neural and biochemical mechanisms. Let's have a closer look at how this works. The retina is a layer of cells at the back of the eye. The portion of the retina across from the pupil that is responsible for the point of focus is called the fovea. The retina comprises cone cells and rod cells, named for their respective shapes. The rods are able to function even in low light conditions but they are absent from the fovea. What's the functional difference between rods and cones? In short, details and colors we see are detected by the cones, and the rods allow us to see black and white, and are light sensitive.
Considering these facts, if you're trying to get a glimpse of an object in the dark, like the dresser in your darkened room, it's more efficient to look at something off to the side of it. By looking to the side, you take advantage of the rods, which work better in the dark.
In addition to this, the pupils, the black circles in the middle of your eyes, dilate in response to darkness. It requires less than a minute for your pupil to completely enlarge but it takes approximately 30-45 minutes for your vision to fully adapt. During this time, your eyes become 10,000 times more sensitive to light.
Dark adaptation occurs when you walk into a dark cinema from a well-lit lobby and struggle to find somewhere to sit. But after a few minutes, your eyes adapt to the dark and before you know it, you can see. You'll experience the same thing when you're looking at stars at night. At first you probably won't be able to actually see that many. Keep looking; as your eyes continue to dark adapt, millions of stars will become brighter. It'll always require a few moments until your eyes fully adapt to normal indoor light. Then if you go back outside, those changes will be lost in the blink of an eye.
This is actually why many people don't like to drive at night. When you look right at the lights of an oncoming car, you may find yourself briefly unable to see, until that car passes and your eyes once again adjust to the night light. To prevent this, don't look right at the car's lights, and learn to try to allow your peripheral vision to guide you.
There are numerous conditions that could, hypothetically cause difficulty seeing at night, including: diet-related vitamin deficiencies, macular degeneration
, glaucoma, and others. Should you begin to notice that you have difficulty seeing in the dark, call to make an appointment with one of our eye doctors who will be able to shed some light on the issue.