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charts  B – Letter Chart Measurements  A variety of factors need
to be considered for accurate measurement of letter chart
acuity.  This outline discusses the most important ones.
Frequently Asked Questions:  What is the preferred chart layout?
What should the viewing distance be? What should the
illumination be? What symbols should be used? What display
method should be used?  Snellen Chart  Snellen’s chart (1862)
ETDRS chart (1982) What is the preferred chart layout?  Beyond
the step sizes discussed earlier, another factor that affects
the measurement accuracy of letter charts is the number of
letters on each line.  Traditional charts have a rectangular
format.  This allows many small letters, but only one or two big
letters on a line.  In 1976 Bailey and Lovie (then in Melbourne)
proposed a new layout, combining the logarithmic progression
with 5 letters on every line and spacing equal to the letter
size.  Their design produced a much wider cha