Saturday, February 23, 2008

Today's Rotary Meeting Was Good For The Eyes!

Eye Charts were everywhere in sight as the MV Rotary celebrated Hermann Snellen's birthday. Hermann, was a Dutch ophthalmologist who was born February 19, 1834 and is the inventor of the Snellen Eye Chart.

JAD Duggan, Club Advisor, and MV Rotary's resident eye Doctor, demonstrated several charts and explained explained to members how the charts work.

The traditional Snellen chart is printed with eleven lines of block letters. The first line consists of one very large letter, which may be one of several letters, for example E, H, N, or A. Subsequent rows have increasing numbers of letters that decrease in size. A patient taking the test covers one eye and reads aloud the letters of each row, beginning at the top. The smallest row that can be read accurately indicates the patient's visual acuity in that eye.

JAD showed the group that if you can read the bottom row, you have 20/10 vision. He said that Ted Williams, baseball player for the Red Sox, had 20/10 vision.

The symbols on a chart are formally known as "optotypes." In the case of the traditional Snellen chart, the optotypes have the appearance of block letters, and are intended to be seen and read as letters. They are not, however, letters from any ordinary typographer's font. They have a particular, simple geometry in which:

  • the thickness of the lines equals the thickness of the white spaces between lines and the thickness of the gap in the letter "C"
  • the height and width of the optotype (letter) is five times the thickness of the line.

Only the ten letters C, D, E, F, L, N, O, P, T, Z are used in the traditional Snellen chart.

Jad brought with him several charts including one that he uses for children. The kids chart showed symbols rather than letters. He even has cards with an E on it so that parents an take them home and have their children practice with it. Sort of like studying for your Eye Tests.

The presentation had one member exclaim:

"Today's meeting was brought to us by the letter E."

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