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The AVTS Vision Test: A Replacement For The 150 Year-Old Eye Chart
Combining modern testing methods and technology we can get a more accurate assessment of vision
We’ve been using the same eye chart for 150 years to test our vision. The chart was designed by Hermann Snellen, a Dutch Ophthalmologist in 1862, and is commonly known as the “Snellen chart”. Recently, a new test has been developed which more accurately reflects the visual needs in day to day life. The AVTS test leverages modern statistical methods as well as technology to create a vision test for this century.
The Snellen eye chart
The printed Snellen chart consists of lines of block letters, arranged in progressively smaller sizes. The Snellen chart is typically hung on a wall, with the patient reading the letters from a distance of 20 feet. The lines on a Snellen chart usually contains letters of different sizes, ranging from the largest at the top to the smallest at the bottom.
All of the characters on the chart are capital letters, written in a block font, in a 5:1 ratio. The ratio is important as it limits, in some cases, which letters can be shown on the chart.
The Snellen chart was designed to test the clarity and sharpness of the subject’s vision. The subject is asked to cover one eye and read aloud the characters from the chart, beginning with the largest letters at the top. As the subject reads each line, their visual acuity is determined by their ability to identify the letters correctly as well as the smallest line they can successfully read. Visual acuity measurements taken using the Snellen chart are usually expressed in the form of a fraction. The fraction consists of the distance of the chart from the subject as the numerator and the size of the letters in the smallest row they can read successfully as the denominator.
For more than a century the Snellen chart has been a valuable tool in determining the clarity of a person’s vision. Unfortunately, as we will see below, there are several problems with the Snellen chart, all of which can be remedied with modern…