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A Closer Look at Night Vision

Something wakes you up in the middle of the night, or you're looking for the light switch or door in a dark room. We've all found ourselves in the dark before. Your eyes normally require a few minutes to adjust to the dark and then you can see again. This process, ''dark adaptation,'' causes people to see even when there's almost no light.

Many people don't know that night vision is dependent upon several physical, neural and biochemical mechanisms. How do our eyes actually function in the dark? Let's examine some eye anatomy. The retina is a layer of cells at the back of the eye. The portion of the retina directly across from 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 rod cells are able to function more efficiently than cone cells in low light conditions. They are not found in the fovea. As you may know, the details and colors we see are detected by the cones, and the rods let us see black and white, and are light sensitive.

Now that you know some background, let's relate it to dark adaptation. If you're looking at an object in the dark, like the edge of the last stair in a dark basement, instead of looking right at it, try to use your peripheral vision. Since there no rods in the fovea, you'll see better if you avoid using it when it's dim.

In addition to this, the pupils dilate in the dark. The pupil dilates to its maximum size in less than a minute; however, dark adaptation keeps enhacing your vision for the next half hour and, as everyone has experienced, during this time, your ability to see despite the darkness will increase enormously.

You'll experience dark adaptation when you walk into a dark movie theatre from a well-lit area and have a hard time finding somewhere to sit. But after a few minutes, your eyes adapt to the dark and see better. You'll experience a very similar phenomenon when you're looking at stars at night. At first you can't see very many. Keep looking; while you dark adapt, the stars will gradually appear. Even though it takes a few noticeable moments to get used to the darker conditions, you'll quickly be able to re-adapt upon your return to bright light, but then the dark adaptation process will have to begin from scratch if you go back into the dark.

This is actually why so many people have difficulty driving their cars at night. If you look directly at the ''brights'' of an oncoming car in traffic, you may find yourself momentarily blinded, until that car passes and your eyes readjust to the night light. To prevent this, don't look right at headlights, and instead, try to allow your peripheral vision to guide you.

If you're beginning to find it increasingly difficult to see at night or in the dark, book an appointment with your eye care professional who will check that your prescription is up to date, and eliminate other and perhaps more serious reasons for poor night vision, like cataracts and macular degeneration.

Welcome to Texas State Optical Northline

Welcome to Texas State Optical Northline

Welcome to TSO Northline

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