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The Mechanics of Night Vision

Everyone's found themselves in the dark, at one time or another. At first you can't see, but gradually the things in the room begin take shape. This is called ''dark adaptation'' and it helps our eyes see in the dark.

In order for night vision and dark adaptation to be successful, many physiological, neurological and biochemical mechanisms have to take place behind the scenes. But how does this work? The human eye has, in addition to other cells, rod cells and cone cells, at the back of the eye; or, to be precise, on the retina. Together they make up the sensory layer that enables the eye to pick up light and color. These cells are spread throughout the entire retina, save for the small area opposite the pupil known as the fovea. This is made up of only cone cells, and its main function involves creating a focused image. What's the difference between these two cell types? In short, details and colors we see are sensed by cone cells, while rod cells let us see black and white, and are light sensitive and detect movement.

This information is significant because, when you're struggling to focus on something in the dark, like a distant star in the night sky, you'll be better off if you view it with the side of your eye. It works by using the light-sensitive rod cells.

In addition to this, the pupils dilate when it's dark. It takes less than a minute for your pupil to fully enlarge; however, it takes about 30 minutes for your eyes to fully adapt and, as you've experienced, during this time, your ability to see despite the darkness will increase remarkably.

Dark adaptation occurs when you walk into a dark theatre from a bright lobby and struggle to find somewhere to sit. But after a few minutes, your eyes get used to the dark and see better. You'll experience the same thing when you're looking at the stars in the sky. At the beginning, you can't see very many. Keep looking; while you dark adapt, millions of stars will gradually appear. It'll always require a few moments until you begin to adapt to regular indoor light. Then if you go back into the brightness, that dark adaptation will be lost in a flash.

This explains one reason behind why many people have difficulty driving their cars at night. When you look directly at the lights of an oncoming car, you are momentarily blinded, until that car is gone and your eyes once again adjust to the night light. To prevent this, try not to look right at headlights, and learn to use your peripheral vision to observe oncoming traffic at night.

There are a number of conditions that can cause inability to see at night. These include not getting enough Vitamin A in your diet, cataracts, glaucoma, or some other visual impediment. Should you begin to detect that you experience trouble in the dark, call to make an appointment with one of our eye care professionals who will be able to get to the root of the problem.


Please be advised that all office visits including exams, frame selections, repairs, pick-ups, and drop-offs are by appointment only. We are required to wear a face mask in our office and ask that you bring yours to your appointment.

We are happy to serve our patients and community and are committed to keeping you as safe as possible.

Thank you.

The Shuswap Optometric Team