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Seeing in the Dark

owlYou're ready for bed and turn out the lights, but you can't fall asleep so you open your eyes and find yourself surrounded by darkness.  It takes a few minutes for your eyes to adjust to the darkness.  This process known as dark adaptation, allows our eyes to adjust to low light settings and involves a combination of biochemical, physical and neural mechanisms.

So how do your eyes adapt to low light?  Let’s start by exploring some eye anatomy.  The human eye has rod cells and cone cells in the retina at the back of the eye, which form the sensory layer that enable the eye to detect light and color. These cells are distributed evenly throughout the retina except for the small area opposite the pupil known as the fovea, where there are only cone cells.  You may have heard that the “cones perceive color” and detail, while the rods help us see “black and white” (and detect movement). This is significant because there are no rods, which are more sensitive to low light, in the fovea, which is used for detailed vision such as reading. So when you are trying to see something in low light, like a dim star in the sky, don't look directly at it. By using your peripheral vision, looking just to the side of the star, you are using more rod cells, which work much better in low light situations.

Dark adaptation also occurs when you go from a very bright area to a dim area, for example walking inside after sitting in the sun.  It takes a few noticeable moments for our eyes to adjust to regular indoor light, but if you walk back out into the brightness, that dark adaptation will be lost in a flash.  If you find it increasingly difficult to see at night or in the dark, schedule an appointment with our doctors who will make sure your prescription is up to date and rule out other reasons for decreased vision such as cataracts and macular degeneration.


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