You wake suddenly, in the middle of the night, or you're trying to find the light switch or door in the dark. It's happened to all of us. It takes a couple of minutes for your vision to return. This process is known as ''dark adaptation'' and it lets our eyes adjust to the dark.
In order for night vision and dark adaptation to happen, many physiological, neurological and biochemical mechanisms must take place behind the scenes. So how does this work? The retina is a layer of cells at the back of the eye. The area of the retina directly opposite 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 even in low light conditions. They are not found in the fovea. What's the functional difference between these two cell types? In short, details and colors we see are sensed by the cones, and the rods let us see black and white, and are light sensitive.
This information is significant because, when trying to see an object in the dark, like the dresser in your darkened room, instead of focusing right on it, try to look just beside it. Since there no rods in the fovea, you'll see better if you avoid using it when it's dim.
The pupils also dilate in low light. It requires fewer than sixty seconds for your pupil to fully enlarge; however, your eyes will continue to adapt over a 30 minute time frame.
You'll experience dark adaptation when you walk into a dark movie theatre from a bright area and have a hard time finding somewhere to sit. But after a few minutes, 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. Initially, you won't see many. As you keep staring, your eyes will dark adapt and the stars will gradually appear. It takes a few noticeable moments for your eyes to adjust to normal indoor light. If you go back into the brightness, those changes will be lost in a moment.
This is actually one reason behind why so many people have difficulty driving their cars at night. If you look at the headlights of opposing traffic, you are briefly unable to see, until that car passes and you readjust to the night light. A helpful way to avoid this is to avoid looking directly at headlights, and instead, use peripheral vision to observe oncoming traffic at night.
There are several things that could potentially cause trouble seeing at night. These include not getting enough Vitamin A in your diet, cataracts, glaucoma, or some other visual interference. Should you begin to suspect difficulty with night vision, call to make an appointment with one of our eye care professionals who will be able to shed some light on why this is happening.