Test–retest reliability of contrast visual acuities in a clinical population

Background: Previously, contrast visual acuities (VA) have been evaluated as a potential screening, diagnostic and predictive tool in cases where standard visual acuity remains intact. Issues around contrast acuity sometimes make it difficult for clinicians to make appropriate clinical decisions and thus such tests have to be standardised and reliable.Aim: To investigate test–retest reliability of contrast VA in healthy adults in a clinical setting.Methods: Best compensated contrast VA at 100%, 10%, 5% and 2.5% of 155 patients (mean age 39.7 ± 12.2 years) were measured using the computerised Thomson Test Chart 2000 Expert. For all participants and at each contrast level, two measurements per right eye were determined. Test–retest reliability for the four contrast levels were assessed using reliability coefficients and Bland–Altman plots. Participants were also divided into three age groups of young (18–39 years, n = 72), middle-age (40–49 years, n = 45) and elderly (50–67 years, n = 38) and reliability was assessed within and between age and gender groups.Results: For the whole-sample test and retest, measurements within each contrast level were not statistically different (p ≥ 0.05). Thus, test and retest measurements per participant were averaged and whole-sample mean-contrast VA and standard deviations for 100%, 10%, 5% and 2.5% were -0.146 ± 0.060, 0.050 ± 0.071, 0.135 ± 0.079 and 0.405 ± 0.115 logMAR, respectively. Significant differences were found between all pairs of contrast levels compared (p ≤ 0.0125). Mean-contrast VA within each age group were also significantly different across all contrast levels (p < 0.0001). Mean-contrast VA at each contrast level between the age groups indicated that mean-contrast VA were not significantly different between the young and middle-age groups (p > 0.05) but were statistically different between the young and elderly groups (p < 0.01). Only mean-contrast VA 10% was significantly different between the middle-age and elderly groups (p < 0.001). Also, mean-contrast VA for the four contrast levels within gender were significantly different (p ≤ 0.05) but not between genders (p ≥ 0.05).Conclusion: This study found good reliability of test and retest measurements of contrast VA in an adult clinical population.