REPEATABILITY OF VISUAL-ACUITY MEASUREMENT

Purpose, This study investigates features of visual acuity chart desig n and acuity testing scoring methods which affect the validity and rep eatability of visual acuity measurements, Methods, Visual acuity was m easured using the Sloan and British Standard letter series, and Landol t rings. Identifiability of the different letters as a function of siz e was estimated, and expressed in the form of frequency-of-seeing curv es. These functions were then used to simulate acuity measurements wit h a variety of chart designs and scoring criteria, Results, Systematic relationships exist between chart design parameters and acuity score, and acuity score repeatability, In particular, an important feature o f a chart, that largely determines the repeatability of visual acuity measurement, is the amount of size change attributed to each letter. T he methods used to score visual acuity performance also affect repeata bility. Conclusions, It is possible to evaluate acuity score validity and repeatability using the statistical principles discussed here.