RELIABILITY OF LOW-CONTRAST LETTER CHARTS IN VARIOUS VIEWING CONDITIONS

Test-retest data were obtained binocularly, monocularly and monocularl y in the presence of glare from 20 healthy older patients using the Pe lli-Robson and Regan (96% and 11% contrast) charts. Reliability was as sessed by means of two indices: intra-class correlation coefficient an d coefficient of repeatability which determines the 95% confidence lim its for change. Binocular viewing showed the highest intra-class corre lation and the smallest confidence interval with all the charts. Monoc ular viewing in the presence of glare showed the lowest correlation an d the largest confidence interval. Results suggest that when assessing the significance of change, the confidence interval should be determi ned for identical viewing conditions.