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Seeing in the Dark

You wake from a dream in the middle of the night, or you're searching for the light switch or door in the dark. We've all found ourselves in the dark before. Gradually, the things in the room begin take shape. This process, called ''dark adaptation,'' allows people to adjust to the dark.

In order for night vision and dark adaptation to occur, many physiological, neurological and biochemical mechanisms have to take place behind the scenes. So how does this work? The retina is a layer of cells at the back of the eye. The section of the retina behind the pupil which produces the point of focus is called the fovea. The retina comprises cone cells and rod cells, named for their respective shapes. The rods have the capacity to function more efficiently than cone cells in low light conditions but those cells are absent from the fovea. What's the functional difference between rods and cones? In short, cones enable us to perceive color and detail, and rod cells help us visualize black and white, and are light sensitive.

This information is significant because, when you want to see something in the dark, like the dresser in your darkened room, it's much more efficient to try to look at it with your peripheral vision. If, on the other hand, you focus on the object itself, you'll use the fovea, which is made up of cone cells that are less responsive in low light conditions.

The pupils also dilate in the dark. It takes less than a minute for your pupil to fully enlarge; however, it takes approximately half an hour for the eye to fully adapt and, as you've experienced, during this time, your ability to see in the dark will increase greatly.

Here's an example of dark adaptation: if you leave a bright area and enter a dim one, for example, walking inside after sitting in the sun. While your eyes require a few noticeable moments to begin to see in the darker conditions, you will immediately be able to re-adapt to exposure to bright light, but then the dark adaptation process will have to begin from scratch if you go back into the dark.

This explains why many people don't like to drive when it's dark. When you look right at the ''brights'' of an oncoming car, you are briefly blinded, 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 to observe oncoming traffic at night.

If you're finding it challenging to see when it's dark, book a consultation with your eye care professional who will explore the reasons this might be happening, and rule out other reasons for decreased vision, such as cataracts and macular degeneration.

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