Vision is a complex process, and many people don t realize that it involves both your eyes and your brain. Eyesight is a big part of how well you see, but having clear vision requires some additional skills. . If you don t have an eye doctor, check out our vision care site for a complete listing of vision careresources and the eye doctors in your area.

Visual acuity is defined as the sharpness of your vision or how clearly you see things. During an eye exam, your vision is tested for both distance and near visual acuity. Distance visual acuity is tested at a distance of 20 feet. Near visual acuity is normally tested at the average reading distance, which is 16 inches.

Both tests are done using a set of lines of letters in incrementally smaller sizes to evaluate a person s eyesight. This form of testing began in the early 1800s and is called the Snellen fraction. This name comes from the Dutch Ophthalmologist Hermann Snellen who developed the letter chart we use today. Many people may recognize the term "Snellen fraction," but many more are familiar with the term  20/20. 

When you hear your doctor say that your vision is  twenty-twenty,  you associate that with perfect eyesight even though you probably don t have a solid understanding as to what this figure really means. The top number in the Snellen fraction is always 20 and refers to the visual acuity testing distance, which is 20 feet. The bottom number of the fraction describes the distance from which a person can recognize the smallest letters on the chart in relation to the average person. For example, if your doctor says that you have 20/40 vision, this means that a person with normal eyesight can read from a distance of 40 feet the smallest line of letters that you can read at 20 feet. In other words, this means that your vision is only half as clear as of the eyesight of a person with 20/20 vision.

How well our eyes work together affects how clear our vision is overall. Having 20/20 vision doesn t always guarantee perfect vision. Reading an eye chart is one specific visual task. Our daily activities, such as reading and working on a computer, require a higher level of performance from our eyes.

Binocular vision refers to our eyes working together as a team. Each eye can have 20/20 vision, but if the eyes aren t properly aligned or working together, they can cause headaches, blurred vision and eyestrain. Binocular vision can cause reading problems for school-aged children and extreme discomfort for adults that leads to health issues and problems completing tasks at school and work. Problems with binocular vision can be treated with vision therapy and special prescription eyewear.

Your eyesight and how well it functions is quite complex. Keeping on top of your vision and eye health is extremely important. When your eyes aren t functioning correctly, it can negatively affect your productivity at work, school and in your daily activities.