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Night Vision

You wake from a dream in the middle of the night, or you’re looking for the light switch or door in the dark. It’s happened to all of us. You need several moments to get used to the dark and then you are able to see better. We call this ”dark adaptation”.

In order for night vision and dark adaptation to work, many physiological, neurological and biochemical mechanisms must take place behind the scenes. So how does this work? The human eye uses rod cells and cone cells, which are found on the retina at the back of the eye. Together they form the sensory layer. This is the part that gives your eye the ability to pick up light and color. The rod and cone cells exist throughout your retina, save for the small area opposite the pupil known as the fovea. The fovea has only cone cells, and its main function involves creating a focused image. You may have heard that the details and colors we see are sensed by cone cells, and rod cells help us visualize black and white, and are light sensitive and detect movement.

So, if struggling to view something in the dark, you’ll be better off if you look at something right next to it. That way, you’re avoiding the use of the fovea, which only has cells that are less sensitive to low light.

Your pupils also dilate in response to darkness. It takes less than a minute for your pupil to completely enlarge; however, your eyes will keep adapting over a 30 minute time frame and, as you’ve experienced, during this time, your ability to see in the low light setting will increase greatly.

Here’s an example of dark adaptation: when you first enter a dark cinema from a well-lit lobby and have a hard time locating somewhere to sit. But soon enough, your eyes adapt to the situation and see better. You’ll experience a very similar feeling when you’re looking at the stars in the sky. Initially, you can’t see very many. Keep looking; while you dark adapt, millions of stars will gradually appear. It takes a few noticeable moments until your eyes fully adjust to normal indoor light. Then if you walk back out into the brightness, those changes will be lost in a flash.

This explains one reason behind why so many people don’t like to drive at night. If you look directly at the lights of opposing traffic, you are briefly unable to see, until that car is gone and you once again adjust to the night light. To prevent this, try not to look right at headlights, and instead, try to allow peripheral vision to guide you.

There are numerous things that could, hypothetically lead to trouble seeing at night. These include a nutritional deficiency, cataracts, glaucoma, or some other visual impediment. If you notice that you experience difficulty seeing in the dark, schedule an appointment with one of our eye doctors who will be able to identify and rectify it.