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Home » What's New » Frederick, MD Eye Exams: Exploring the Eye Chart

Frederick, MD Eye Exams: Exploring the Eye Chart


Have you ever asked yourself what 20/20 vision actually means? 20/20 vision is a phrase to express normal visual acuity or clarity of vision. In other words an individual with such visual acuity can clearly see an object at a distance of 20 feet that most people should be able to see from such a distance.

In cases of individuals that cannot see an object clearly at 20/20, their visual acuity score is designated based on where they begin to see clearly compared to what is normally expected. As an example, 20/100 vision indicates that at a distance of 20 feet you can only see an object that a person with normal vision can see from 100 feet distance.

You can also have vision that is above 20/20. For example a person with 20/10 eyesight can see clearly at 20 feet what the average person can only see at 10 feet distance. Certain animals have more acute vision in comparison to the human species. For example, hawks have been known to have 20/2 vision, enabling them to locate prey from great heights.

Most eye care professionals employ some version of the Snellen eye chart, developed by Dutch eye doctor, Herman Snellen in the mid-1800's, to conduct an eye screening. While there are many versions, the chart typically shows 11 lines with uppercase letters which get smaller in size as one looks downward. The top of the chart usually shows one capital letter - ''E'' and gradually includes more letters on the lines as they get smaller. During the eye exam, the optometrist will determine which is the line with the smallest lettering you can make out. Every line is assigned a distance, with the 20/20 row usually being ascribed the eighth row. In instances where the patient can't read, such as young children or disabled persons, the ''Tumbling E'' chart is employed. At the same scale as the standard Snellen chart, the ''Tumbling E'' shows only the uppercase letter E in different directions. The eye doctor tells the patient to show which rotational direction the ''fingers'' of the E are pointing.. Both charts needs to be placed 20 feet away from the patient's eyes.

Although 20/20 vision does show that an individual is able to see as expected from a distance this measure on its own does not imply that someone has flawless eyesight. ''Perfect'' eyesight involves a number of other necessary abilities such as peripheral vision, depth perception, focus for near vision, color vision and coordination between the eyes to name a few.

It's important to remember that even though an eye exam using a Snellen chart will establish if you need eyeglasses to improve distance vision it will not provide the optometrist a complete picture of the total status of your eyes and vision. Make sure you still schedule an annual comprehensive eye exam to screen for vision-threatening diseases. Call us now to schedule an eye exam in Frederick, MD.