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Night Vision

owlImagine your house loses power and suddenly, you need to find a flashlight or the fuse box. After a few moments you begin to recognize familiar things in your surroundings. This process, “dark adaptation,” allows our vision to adjust to the dark.

Many people don’t know that night vision relies on several physical, neural and biochemical mechanisms. So how does this work? The retina is a layer of cells at the back of the eye. The portion of the retina directly behind the pupil that is responsible for sharp focused vision is called the fovea. The retina is made up of cone cells and rod cells, named for their respective shapes. The rods are able to function more efficiently than cone cells in low light conditions but they are absent from the fovea. What’s the functional difference between rods and cones? In short, cones contribute to color vision, while the rods are sensitive to light.

Let’s put this all together. Imagine you’re struggling to view something in the dark, instead of focusing right on it, try to use your peripheral vision. By looking to the side, you take advantage of the rods, which work better in the dark.

The pupils also dilate in response to darkness. It takes fewer than sixty seconds for the pupil to completely dilate but your eyes will keep getting used to the dark over a 30 minute period. During this time, sensitivity to light increases by a factor of 10,000 or more.

Dark adaptation occurs when you leave a bright area and enter a dim one, for example, walking inside after sitting in the sun. While you need several moments to adapt to the darker conditions, you’ll quickly be able to re-adapt to exposure to bright light, but if you return to the darker setting, your eyes will need time to adjust again.

This is why many people don’t like to drive at night. If you look right at the lights of a car heading toward you, you may find yourself momentarily unable to see, until that car passes and you once again adjust to the night light. To prevent this, try not to look right at the car’s lights, and instead, use your peripheral vision to observe oncoming traffic at night.

If you’re beginning to find it harder 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 and perhaps more severe reasons for worsening vision, like cataracts and macular degeneration.

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