I recently joined Stroud Artists' Books at Stroud Valley Arts, a space for artists to meet up monthly and share their ideas for books and practice.
Each month there is a theme, and the theme for February was the Lens, and I used the format of a maze book.
In my trawl around the net I discovered that the letters used in an eye test are Optotypes (test symbols).
They are not, however, letters from any ordinary typographer's font, they have their own particular, simple geometry in which the thickness of the line equals the thickness of the white spaces between the lines, and the height and the width is five times the thickness of the line . . .
The type in the title is designed to fade away . . . just as our eye sight is prone to do with age!