The Effect of Cataract on Color Vision Measurement with the Low-Vision Cambridge Colour Test

Purpose: To quantify the effect of cataract on colour vision as measured by the low vision Cambridge Colour Test (lvCCT). A secondary aim of our study was to understand whether different types and severities of cataract have different effects on colour vision. Design: Cohort study Subjects: Patients aged 18 - 95 years attending for routine cataract surgery at the Oxford Eye Hospital. Methods: The lvCCT was performed to measure colour sensitivity in both eyes in a cohort of patients undergoing routine cataract surgery both pre-operatively and post-operatively. The crystalline lens was examined and graded according to the Lens Opacities Classification System III (LOCS III) to determine the type and severity of cataract. Measures of repeatability were performed for the data to explore test-retest bias using Bland-Altman analysis. The Wilcoxon signed-rank test was performed to assess the effect of cataract on colour vision by comparing control and surgical test measurements. Three multiple linear regressions were performed to relate cataract grading or severity to colour vision measurements. Main outcome measures: Colour discrimination along each of the protan, deutan, and tritan confusion lines. Results: The Wilcoxon signed-rank test showed a statistically significant difference in both the protan (P=0.024) and tritan (P=0.020) axes upon comparison of control and surgical test measurements. As severity of cataract increased colour vision sensitivity was more greatly affected, and nuclear sclerotic cataract had the most profound effect upon colour vision sensitivity in the lvCCT. The linear regression models though showed these observations did not reach statistical significance. Conclusions: Cataract surgery has a statistically significant effect upon colour vision in both the protan and tritan axes. The effects of specific subtypes of cataract and different severities could not be elucidated due to the high prevalence of patients presenting with mixed cataract. LvCCT colour sensitivity measurements are regularly used as outcome measures in clinical gene therapy trials involving vitreoretinal surgery, and vitrectomy accelerates cataract formation. Therefore, it is important to quantify the effect of cataract upon colour vision measurements so it may be taken into account when used as an outcome measure in clinical trials. We were unable to derive a precise correction factor for cataract on color vision measurements.