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.