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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. At first you can't see, but gradually the things in the room begin become visible. We call this ''dark adaptation'' and it's what helps our eyes get used to the dark.

In order for night vision and dark adaptation to occur, several physiological, neurological and biochemical mechanisms have to take place behind the scenes. Let's talk about how your eye actually operates in these conditions. The retina is a layer of cells at the back of the eye. The portion of the retina opposite the pupil which produces the point of focus is called the fovea. The retina comprises rod-shaped and cone-shaped cells. The rods are able to function more efficiently than cone cells in low light conditions but those cells are not found in the fovea. What's the difference between rods and cones? Basically, cones enable us to perceive color and detail, while the rods allow us to see black and white, and are light sensitive.

So, if trying to get a glimpse of an object in the dark, like the edge of the last stair in a dark basement, instead of focusing right on it, try to look just beside it. It works by taking advantage of the light-sensitive rod cells.

Furthermore, the pupils, the black circles in the middle of your eyes, dilate when it's dark. It takes fewer than sixty seconds for your pupil to completely enlarge; however, it takes approximately 30 minutes for you to fully adapt and, as everyone has experienced, during this time, your ability to see will increase greatly.

Here's an example of dark adaptation: when you enter a dark cinema from a well-lit lobby and struggle to find somewhere to sit. But soon enough, your eyes adapt to the situation and before you know it, you can see. This same thing occurs when you're looking at the stars in the sky. Initially, you won't see many. Keep looking; as your eyes continue to dark adapt, millions of stars will become brighter. It takes a few noticeable moments for your eyes to adjust to normal indoor light. Then if you walk back out into the brightness, those changes will be lost in a moment.

This is actually why many people have trouble driving at night. If you look at the headlights of opposing traffic, you may find yourself momentarily blinded, until that car passes and you once again adjust to the night light. To prevent this, don't look right at the car's lights, and instead, try to allow your peripheral vision to guide you.

There are numerous conditions that could potentially cause trouble seeing at night. These include diet-related vitamin deficiencies, macular degeneration, cataracts, glaucoma, and others. If you detect that you have problems with night vision, call to make an appointment with one of our eye care professionals who will be able to shed some light on why this is happening.