For vision testing at 3 meters (10 ft.) Acuity range 30M to 1.5M (20/200, 6/60 to 20/10, 6/3 equiv.
Only standardized format accepted in studies sponsored by the National Eye Institute
Lines are of equal difficulty
Letter size is only variable
Measures 62 X 65 cm (24.5 X 25.5 in.)
Eye chart fits the ETDRS Illuminator Cabinet CAT. NO. 2425
Can be wall-mounted
Logarithmic notations
ETDRS acuity charts use 5 equally difficult optotypes per line. Other charts may use different amounts of optotypes per line which make measuring acuity levels more difficult and unreliable. Also, ETDRS eye tests use a geometric progression from line to line to eliminate problems with loss and gain and make the test more constant. Equal difficulty in optotypes and lines coupled with geometric progression create a highly calibrated eye test usable in clinical trials, low vision evaluations, and various studies where repeatable visual acuity measurements are not only important, but are required.
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