The influence of color filters and induced defocus on contrast sensitivity function

PURPOSE: To evaluate the influence of color filters and induced defocus, both separately and combined, on the contrast sensitivity function (CSF) in emmetropic and myopic eyes. METHODS: This prospective study included 19 emmetropic and 11 myopic eyes of participants, aged 20-35 years. After cycloplegia, the CSF was evaluated using the Optec Functional Vision Analyzer (FVA). Each assessment was performed while wearing the best correction, as well as six levels of defocus between ±1.5 D. This series was repeated with a superimposed green, red, or blue color filter, applied in random order. RESULTS: The CSF values decreased with increasing spatial frequency for all colors and defocus levels. Defocus of either sign significantly decreased the CSF in both emmetropes and myopes, but myopes experienced a greater CSF reduction than emmetropes. This is also seen for the color filters. Wearing the green filter, or no filter, produced the highest CSF values, while the blue yielded the lowest values (e.g., the CS at 18 cpd in emmetropes was 1.11 ± 0.18 and 0.73 ± 0.16, for the green and blue filters, respectively). However, in myopes, no significant differences in CSF were observed between the various color filters. Using linear mixed-effects models, a significant interaction between defocus and color filter emerged at 3 and 6 cpd (p < 0.001), indicating that defocus and color filters did not act independently across all spatial frequencies. CONCLUSIONS: Defocus and color filters affected the CSF largely independently at low (1.5 cpd) and high (12-18 cpd) spatial frequencies in emmetropes but interacted significantly at intermediate frequencies (3 and 6 cpd), indicating their combined effects are not uniformly independent. Color filters had no statistically significant impact on the CSF of myopes in this study.