The LEA Symbols optotypes were originally designed by Lea Hyvärinen, MD in 1976 and calibrated against the Snellen E, the international reference optotype of those days. Designing these four optotypes required much more work than one would imagine. The LEA apple and house were carefully developed and tested to insure they are equally legible with the square and the circle. Further refinement and testing of the LEA Symbols  was performed in 1988 against the another emerging standard, the Landolt C, to insure corresponding acuity measurement. LEA Symbols have shown a high sensitivity for amblyopia without some of the shortcomings of the Landolt C optotype.

LEA Numbers Tests were developed for international studies in occupational health and school health services. Letters like the Sloan letters are used in the Western world and in the old colonies of western empires but not in a large part of the rest of the world whereas numbers are the same almost world over. The four numbers 5,6,8 and 9 were chosen because they could be designed to blur equally. Numerous hours were spent refining the details of each number. This makes the threshold value much narrower than in older tests where such easy numbers as 2, 4 and 7 are used. In clinical use of visual acuity tests letters and numbers are generally used instead of the reference optotype Landolt C or “Ring” although there are countries were Landolt C is used even in pediatric testing. Letter and number optotypes require recognition of the form.

The round numbers 5,6,8 and 9 are more difficult to recognize than it is to detect where the space is in the Landolt C. Calibration of the size of the number optotypes was done by Juvi Mustonen, O.D. and Risto Näsänen Ph.D. at the Vision Laboratory of the Department of Physiology, Helsinki University, Finland.

LEA Symbols and LEA Numbers were developed by and are the copyrighted property of Lea Hyvarinen, MD