The reliability of the Pelli‐Robson contrast sensitivity chart

Normative contrast sensitivity (CS) data were obtained using the commercially available Pelli‐Robson chart from the dominant eye of 30 young (mean (±SD) age 22.5 ± 4.3 years) and 42 older (mean (±SD) age 70.2 ± 6.7 years) subjects with normal healthy eyes. The majority of young subjects were found to have a CS of 1.80 log units or above. The majority of the older subjects were found to have a CS of 1.65 log units or above. CS results were obtained using both sides (A and B) of the Pelli‐Robson chart from 30 (15 young and 15 older) of these subjects. These measurements were repeated under identical conditions, 2 weeks later. There was no significant difference between the results from sides A and B of the chart. The CS scores were shown to be repeatable to within ±0.15 log units or ±1 step. Therefore a significant change in CS score is +2 steps or 0.30 log units. Slight improvements in reliability could be obtained by more careful permutation of letters on each step and a smaller step size. The restriction against these changes is the ensuing increased chart size.