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Potomac, MD Eye Exams: Exploring the Vision Chart


Have you ever asked yourself why 20/20 is the standard for ''perfect'' eyesight and what it really represents? 20/20 vision is a term to describe normal visual acuity or clarity of vision. That is to say that an individual with such visual acuity can see an object clearly at a distance of 20 feet which is deemed the norm to see at that distance.

For those who don't have 20/20 vision, the number is assigned according to the first point at which they are able to see clearly, compared to what is normally expected. For instance, 20/100 acuity indicates that you have to be as close as 20 feet to see clearly what a person with normal eyesight can see at 100 feet away.

A person whose eyesight is 20/200 or worse is considered legally blind however, they can often see normally through prescription glasses or contacts or by undergoing LASIK if they are eligible.

Most optometrists utilize a version of the Snellen eye chart, which was invented by Hermann Snellen, a Dutch eye doctor in the mid-1800's, to conduct a vision screening. While there are now many variations, the chart generally shows 11 rows with uppercase letters which get progressively smaller as one looks toward the bottom. The chart begins with the capital letter - ''E'' with letters being added gradually as you look down the chart. During the vision screening, the eye doctor will look for the line with the smallest lettering you can see clearly. Your score is determined since each row is assigned a rating, with the 20/20 row typically being assigned forth from the bottom. In cases in which the patient can't read, such as small children or handicapped individuals, the ''Tumbling E'' chart is employed. Similar to the traditional Snellen chart, this variation portrays only the uppercase letter E in different spatial orientations. The eye doctor tells the patient to show the direction the ''fingers'' of the E are pointing.. Both charts needs to be placed 20 feet away from where the patient is viewing it.

Although 20/20 vision does show that an individual's sight for distances is average, this test on its own does not imply that the individual has flawless eyesight. There are many other essential elements to make perfect vision such as peripheral sight, depth perception, color vision, near vision and focusing and eye coordination to name a few.

While an eye exam using a Snellen chart can establish if you need eyeglasses to correct for distance vision it will not give the eye doctor a comprehensive picture of the complete status of your eyes and vision. You should still schedule an annual comprehensive eye exam to screen for potential diseases. Call us today to book a Potomac, MD eye test.


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