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Eye Health Center

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Understanding Vision Problems -- the Basics

Color Blindness

Color blindness is most commonly a disorder of the retina's light-sensitive photoreceptor cells, which respond to different colored light rays. There are two kinds of photoreceptors:

  • Cones work best in bright light
  • Rods work best in dim light

Each photoreceptor produces pigments that respond to specific colors of light.

Color vision is affected if those pigments are absent or defective or if they respond to the wrong wavelengths.

You have probably seen how paint colors are mixed at the hardware store. Color vision works much the same way because visible light is a mixture of different light rays (wavelengths). Color perception problems occur more often in men, afflicting 8% of the male population. Females tend to be the "carrier" of the trait. It is extremely rare for someone to be totally color-blind, that is, able to see only shades of gray.

Night Blindness

Night blindness -- difficulty seeing in dim light -- occurs when rod photoreceptor cells begin to deteriorate. Rods work best in low light. There are many different forms of night blindness, but it may be linked to these conditions:



Eyestrain can occur simply from overusing your eyes for long periods of time. Eyestrain is discomfort that can also be due to an uncorrected refractive problem. This common vision problem may occur while you are performing distant visual activities like driving or watching a movie or during close-up tasks like reading and computer use.

Familiar symptoms of eyestrain include:

Eyestrain quickly goes away if the eyes are given a chance to rest or the refractive problem is resolved. Prolonged focusing can lead to eyestrain, such as working at the computer for hours. Children have a far more flexible focusing capacity. How often do you ever hear a child complain of eyestrain while playing video games?

If you wear prescription glasses, recurring eyestrain may be an indication that you need updated glasses or a new prescription. Eye exercises or resting the eyes every hour helps relieve eyestrain, especially when working with computers.

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