THE PURPOSE of this review is to investigate the relative merits of different test objects and procedures used to measure visual acuity, with particular emphasis on their suitability as selection tests for industry, the military services, etc., and as screening tests for the detection of errors of refraction or other visual defects. Adoption of a standard procedure for the measurement of individual differences in acuity which gives valid and precise measures and is at the same time simple and practical requires consideration of the following points: (1) selection of the most suitable type of test object; (2) specification of the range and gradation of the sizes of test object required, and (3) standardization of the brightness of test object and background and of other variable factors in the test procedure.
RELATIVE MERITS OF DIFFERENT TYPES OF TEST OBJECTS
In an excellent review Cowan