By P. Kay Nottingham Chaplin, Ed.D. Director – Vision and Eye Health Initiatives – School Health Corporation and The Good-Lite Company
Standardized eye charts help to ensure the visual acuity task is equal on any line of a chart. Though one of the earliest attempts at eye chart standardization occurred in 1835 or 1836 (no, this is not a typo), did you know many front line screeners today use eye charts that are not standardized?
A Brief History
Heinrich Küchler, a physician from Darmstadt, Germany, is credited with creating the first symbol eye chart in 1835 or 1836 (Runge, 2000). In a creative effort, Küchler cut small figures from calendars, think almanacs, and glued the figures to paper in decreasing size. Figures included people, cannons, guns, birds, farm equipment, camels, and frogs.
However, he recognized two possible problems with his symbol eye chart. First, his figures lacked consistency in size. Küchler also noted that the frogs, camels, and other figures in his eye chart lacked uniformity in optotype legibility or discriminability. What does this mean? When optotypes lack legibility consistency, some optotypes are easier to distinguish (or even guess), at different points of an eye chart, even on the same line.
To review equal optotype legibility as one of six components of a standardized eye chart, refer to "Selecting an Eye Chart - Sloan Letters of Snellen?">>
Apparently not one to give up pursuing his standardization goal, Küchler, 7 or so years later, published an eye chart using letters arranged in a graduated series. The eye chart consisted of 12 lines with larger letters on the top line. Lines decreased in size to the bottom line. Though the concept remains with us in 2011, Küchler’s chart was not widely used and accepted. It was published only once in 1843.
Incredibly, 175 years later, some eye charts are still not standardized!
Non-Standardized vs. Standardized If you look closely at the optotypes on the Kindergarten Eye Chart (a.k.a. Sailboat chart) you will notice that the optotypes are inconsistent in size. Look specifically at the hand and star on the 20/30 line. This is an example of a current non-standardized eye chart.
Two choices for screening the vision of all ages using standardized eye charts include: Sloan Letters (pictured left) for older children and 10-line LEA Symbols (pictured right) eye chart for younger children who do not yet know their letters.
Have you recently switched from a non-standardized eye chart to a standardized eye chart? We would love to hear from you, either in the comments below or offline via e-mail to Dr. Kay at email@example.com When you respond, please tell us the following:
- Non-standardized chart used
- Standardized chart now using
- Good referrals vs. bad referrals with the non-standardized chart
- Good referrals vs. bad referrals with the standardized chart
REFERENCES: Eye Chart Photo courtesy of Colenbrander (2008) Colenbrander, A. (2008).
The historical evolution of visual acuity measurement. Visual Impairment Research, 10, 57-66.
Runge, P. E. (2000). Eduard Jaeger’s test-types (Schrift-Scalen) and the historical development of vision tests. Transactions of the American Ophthalmological Society, 98, 375-438.