The Kay Letter Test is a linear letter acuity test comprising six of the Sloan letters used in the ETDRS study and regarded as the International Standard. These six letters were chosen as being most suitable for testing younger children. The test displays five letters per acuity size (size 1.0 has 4 letters), as recommended by international standards, with optimal crowing between optotypes and the crowding bars. It contains comprehensive LogMAR sizing at three metres from sizes 1.00 to -0.20, plus near testing with LogMAR letters and high frequency words.