Optonet Vision Unit Documentation
Please note that this User Guide is being currently updated; new sections will be added shortly.
Two versions of British letter charts are included. The first is the classic (1968) standard set which uses the following 10 letters: D, H, N, U, V, F, R, P, E, Z, drawn on a 5×4 matrix, (ratio of height:width is 5:4). The second is a revised standard (2003) in which letters are drawn on a 5×5 matrix (equal height:width) similar to the Snellen “E”. The revised set uses the same letter set plus two additional letters: the “C” and “K” (12 letters in total). All these letters are also considered of similar difficulty9 by British standards.