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The Mechanics of Night Vision

Let’s say your house loses power and suddenly, you need to hunt around for a flashlight or the fuse box. Gradually, the things in the room begin take shape. We call this ”dark adaptation”.

In order for night vision and dark adaptation to be successful, many physiological, neurological and biochemical mechanisms must take place behind the scenes. So how does this work? Every eye contains photoreceptors that can be classified as rod cells and cone cells, on the retina at the back of the eye. Together they form the sensory layer that helps the eye pick up colors and light. These cells are distributed evenly throughout the retina, save for the small area called the fovea, where there are only cone cells. That part is primarily responsible for detailed vision, such as when reading. You may have learned that the cones enable us to perceive color and detail, and rod cells let us see black and white, and are light sensitive and detect movement.

So, if you’re struggling to view something in the dark, like a small star in the night sky, you’ll be better off if you look at the area next to it. It works by utilizing the light-sensitive rod cells.

Another part of the process is pupil dilation. Your pupil grows to it its largest diameter within 60 seconds but dark adaptation continues to improve your eyesight for the next half hour and, as everyone has experienced, during this time, your ability to see will increase greatly.

Here’s an example of dark adaptation: when you first enter a darkened theatre from a well-lit area and have trouble finding somewhere to sit. But after a couple of minutes, you get used to the dark and before you know it, you can see. This same thing occurs when you’re looking at the stars in the sky. Initially, you won’t see many. If you keep looking, your eyes will dark adapt and millions of stars will become easier to see. It takes a few noticeable moments for your eyes to get used to regular indoor light. If you walk back out into the brightness, those changes will vanish in a flash.

This is actually why so many people have difficulty driving their cars at night. If you look at the ”brights” of opposing traffic, you are briefly unable to see, until you pass them and you readjust to the night light. A helpful way to avoid this is to avoid looking directly at the car’s lights, and instead, use peripheral vision in those situations.

If you’re finding it challenging to see when it’s dark, schedule an appointment with our doctors who will be able to look into why this is happening, and eliminate other reasons for decreased vision, such as macular degeneration or cataracts.

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