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Seeing in the Dark

Some nights, you lie in your bed, all ready to dream the night away with the lights off, but you can't fall asleep. You open your eyes and you can't see anything. A number of minutes pass before you begin to recognize familiar things in your surroundings. This process, called ''dark adaptation,'' allows us to see even when there's almost no light.

Many people don't know that night vision relies on the cooperation of physical, neural and biochemical mechanisms. So how do our eyes operate in low light? Firstly, let's examine the eye and its anatomy. The retina is a layer of cells at the back of the eye. The section of the retina directly behind the pupil which produces the point of focus is called the fovea. The retina is made up of rod-shaped and cone-shaped cells. The rods have the capacity to function better than cone cells in low light conditions but those cells are not found in the fovea. You may have heard that the details and colors we see are sensed by the cones, and the rods let us see black and white, and are light sensitive.

So, if you want to see something in the dark, it's more efficient to focus on something off to the side of it. It works by taking advantage of the light-sensitive rod cells.

Another way your eye responds to darkness is by your pupils dilating. It requires approximately one minute for your pupil to completely dilate; however, your eyes will get better at seeing in the dark over a 30 minute time frame and, as everyone has experienced, during this time, your ability to see despite the darkness will increase enormously.

Dark adaptation occurs when you go from a very light-filled place to a dim one for instance, walking inside after spending time in the sun. It'll always take a few moments until your eyes fully adjust to normal indoor light. If you go back into the brightness, those changes will vanish in the blink of an eye.

This is why a lot people don't like to drive at night. When you look at the headlights of opposing traffic, you may find yourself briefly blinded, until that car is gone and your eyes readjust to the night light. To prevent this, try not to look right at the car's lights, and learn to use peripheral vision in those situations.

If you're having trouble seeing when it's dark, schedule an appointment with our doctors who will explore the reasons this might be happening, and rule out other reasons for worsened vision, such as cataracts and macular degeneration.