Why do eye charts always start with "E"?

[MHasegawa]

What's wrong with "K" or "F"??

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[DeltaPin]

So no matter how bad your eyesight, you can always get one line right.

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[TooCute]

I seem to recall that it's because it's on of the hardest letters to idenify, because th three parallel lines have a tendency to get mushed together and hard to distinguish from yes an F or whatever when you can't see very well. So if you can't read the E, you're REALLY screwed.

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[jeffdwright2001]

They don't. Although the one you are probably used to seeing is the Snellen Chart (named for creator Herman Snellen) typically does begin with the letter "E". However, many of the Snellen Charts may start with the letter "A".

There are several other variations of the chart and new charts that work to improve on aspects of the chart that are somewhat flawed in design when it comes to diagnosing someone's "true" vision. The Bailey-Lovie chart is a new design that is starting to become more prevalent among opthamologists.

There is also a variation of the Snellen Chart for those who cannot read. It's made up entirely of the letter "E" facing in different directions (vertically and horizontally) and the person is to tell the doctor which direction the "E" is pointing.

Too Cute is on the right track with the idea of certain letters being more difficult to identify. Snellen used "square" letters which tends to limit the available letters in the alphabet which are available.

I'm not a math kind of guy, but it does have something to do with how the eye responds to the thickness of the letter in proportion to size of the letter and the "distance" from the arc of the eye. So instead of having someone move back and re-reading the line, he adjusted the size and position of the letter to simulate a distance change.

I think the above is basically correct and apologize if there are any errors.

[jeffdwright2001]

forgot to give the name of the Chart with the different facing "E"s.

It's called appropriately enough the "Tumbling E" chart.

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[MHasegawa]

Good enough answer for me, Jeff, danke.

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[Mike Teacher]

Oh yeah the Tumbling E's. I think thats used to test for astigmatism; "do all of the E's look the same, or something."

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[jeffdwright2001]

Oh yeah the Tumbling E's. I think thats used to test for astigmatism; "do all of the E's look the same, or something."
It's actually used to test for the same areas as the Snellen Chart. It's just typically given to those who can't read (especially children).

It's set up the same way and measure far point acuity. A child may not be able to tell you what different letters they are reading, but they CAN tell you which way the leggs are pointing.

[SatCam]

I remember in pre-school we had to identify the direction of the E with our pointer finger, middle finger, and ring finger.

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[Melrapuo]

This Snellen chart starts with an F

http://www.homevisiontherapy.com/snellen.gif

Just google it.

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