Sometimes you go to bed and turn off the light, but you just can’t seem to doze off. You open your eyes and you can’t see anything. You notice that it is almost impossible to see anything for a few moments before your eyes adjust. This is called ”dark adaptation” and it helps our eyes see in the dark.
Many people don’t know that night vision relies on several physical, neural and biochemical mechanisms. So how does it actually work? Firstly, let’s examine some eye anatomy. The retina is a layer of cells at the back of the eye. The portion of the retina behind the pupil which produces sharp focused vision is called the fovea. The retina comprises cone cells and rod cells, named for their respective shapes. The rod cells are able to function even in low light conditions but those cells are not found in the fovea. As you may know, the cones help us perceive color and detail, and rod cells are sensitive to light.
Let’s put this all together. Imagine you’re trying to get a glimpse of an object in the dark, like a small star in a dark sky, instead of focusing right on it, try to use your peripheral vision. That way, you’re avoiding the use of the fovea, which only has cells that are less sensitive to low light.
Also, the pupils, the black circles in the middle of your eyes, dilate in the dark. It requires approximately one minute for the pupil to fully enlarge; however, your eyes will keep adapting over a 30 minute period.
You’ll experience dark adaptation if you exit a bright area and enter a dim one, for instance, walking inside after spending time in the sun. It takes a few noticeable moments until your eyes fully get used to regular indoor light. If you go back outside, those changes will disappear in a moment.
This explains one reason behind why so many people don’t like to drive when it’s dark. If you look directly at the lights of an approaching vehicle, you may find yourself briefly blinded, until you pass them and your eyes readjust to the night light. To prevent this, don’t look right at the car’s lights, and learn to use your peripheral vision in those situations.
There are numerous conditions that could potentially lead to difficulty with night vision. Here are some possibilities: a nutritional deficiency, cataracts, glaucoma, or some other visual impediment. If you notice problems with night vision, call to make an appointment with one of our eye doctors who will be able to identify and rectify it.