Reduced eye optical quality contributes to worse chromatic thresholds in aging

Abstract

Purpose: Aging causes substantial changes in the intraocular lens, which leads to a reduction in chromatic perception. We aimed to measure the ocular light dispersion component in relation to the reduction in color vision by aging.

Methods: Intraocular straylight was quantified psychophysically by C-Quant for light dispersion [Log(s)], reliability of the results (ESD), and psychometric sampling quality (Q). The Cambridge Color Test Trivector protocol measured the chromaticity thresholds for protan, deutan, and tritan color confusion axis in CIE 1976 u' v' units. We tested 224 subjects aged 24-68 years (106 men) with normal best-corrected visual acuity and without clinical evidence of cataracts.

Results: A significant positive correlation was found between ocular dispersion of light and chromaticity thresholds for protan (r = 0.42; p < 0.001), deutan (r = 0.49; p < 0.001) and tritan (r = 0.51; p < 0.0001) color confusion axes with a moderate effect size (η² = 0.39). However, a weak contribution of the logarithm of the straylight in predicting the chromaticity threshold for protan (b = 0.15; p = 0.025), deutan (b = 0.27; p = 0.001) and tritan (b = 0.21; p = 0.001) color confusion axes was verified in the regression coefficients. The other two measurement quality parameters estimated in the C-Quant were not correlated with chromaticity thresholds, suggesting that there are no problems with the quality of the measurement performed.

Conclusion: An increase in ocular light dispersion that occurs physiologically with aging negatively impacts the chromaticity threshold in a similar manner across all three color confusion axes. The weak regression effects suggest that neural rather than optical processes were more related to the reduction in chromaticity in aging.

Keywords: aging; chromaticity threshold; ocular optical quality; ocular straylight; psychophysical.

FIGURE 1

Presentation of the main results for the retinal straylight parameters and for the chromaticity discrimination thresholds for the protan, deutan and tritan color confusion axes in the CCT Trivector protocol. Statistical differences between age groups are marked (*). The Log(s) is the logarithm of the light dispersion; Q is the factor regarding the quality of the straylight curve; estimated standard deviation (ESD) is the expected standard deviation, which measures the reliability of the straylight.

FIGURE 2

Bag plot showing the correlation between the amount of the straylight and the chromaticity thresholds measured in CIE u’ v’ units. Bag plots are the bivariate extension of the univariate box plot that contains 50% of the points similar to the 50% central region of the box-plot and a fence corresponding to an augmented central region by a factor of 1.5 (75% of data). Correlations measured were low-to-moderate for protan (r = 0.42; p < 0.001), deutan (r = 0.49; p < 0.001) and tritan (r = 0.51; p < 0.001) color confusion axes.