IT HAS been evident for many years in my practice in Honolulu that in order to properly test the vision of Japanese who are not familar with English characters a new type of test chart similar to that currently used (Snellen) would be necessary.
Maintaining the requirements of Snellen type, i.e., that it subtend an angle of 5 minutes of arc, presented a considerable problem, owing to the variations in the thickness of Japanese characters, particularly those of the Hiragana and Kanji varieties. These characters of the Katakana division (elementary), however, lent themselves better, to this use, and by modifying these characters slightly, so as to not lose their identity, it has been possible to make them conform to an angle of 5 minutes of arc uniformly. The result is the slide illustrated.
Characters varying from 20/400 to 20/15 are now available in step-down sizes, and a minimum of repetition
CORBOY PM. A JAPANESE PROJECTOCHART SLIDE. AMA Arch Ophthalmol. 1956;56(2):298. doi:10.1001/archopht.1956.00930040306014