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Focusing on Night Vision

It's happened to all of us: there's a blackout and suddenly, you need to hunt around for a flashlight or the fuse box. A number of minutes pass before you can see again. This remarkable process is ''dark adaptation'' and it's what lets our eyes see in low light settings.

A person with a healthy set of eyes probably takes night vision - and the role of the biochemical, physical and neural mechanisms - for granted. Let's have a look at how your eye actually operates in these conditions. Every eye uses rod cells and cone cells, on the retina at the back of the eye. Together they make up the sensory layer that enables the eye to detect colors and light. Cones and rods are distributed evenly throughout your retina, except for in the small area known as the fovea, where there are only cone cells. That part is the part used for detailed vision, for example when reading. You might already be aware that the cones contribute to color vision, while the rods help us visualize black and white, and are light sensitive and detect movement.

Now that you know some background, let's relate it to dark adaptation. If trying to find something in the dark, like a small star in the night sky, instead of looking directly at it, try to look just beside it. 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.

Another process your eye undergoes is pupil dilation. It takes less than a minute for your pupil to completely enlarge but dark adaptation keeps improving your ability to see for the next half hour.

Dark adaptation occurs if you go from a very bright place to a dim one for example, when coming inside after being out in the sun. It'll always require a few moments until you begin to adjust to regular indoor light, but if you go back outside, those changes will disappear in a moment.

This explains why so many people prefer not to drive at night. When you look at the ''brights'' of an oncoming car in traffic, you are momentarily blinded, until that car passes and your eyes readjust to the night light. A helpful way to avoid this is to avoid looking right at the car's lights, and instead, use your peripheral vision to observe oncoming traffic at night.

There are several conditions that could potentially lead to trouble seeing at night, including: diet-related vitamin deficiencies, cataracts, glaucoma, or some other visual obstruction. If you detect that you experience difficulty seeing in the dark, call to make an appointment with one of our eye doctors who will be able to shed some light on the issue.