Chromatic-filter light therapy versus part-time occlusion for unilateral amblyopia: a quasi-experimental longitudinal study.

Purpose

To compare wavelength-specific chromatic-filter light therapy using amber-red, yellow, or orange filters with conventional patching for unilateral amblyopia and to evaluate longitudinal changes in best-corrected visual acuity (BCVA), contrast sensitivity, and stereopsis.

Methods

This assessor-masked, quasi-experimental study included 88 participants aged 5-15 years with unilateral anisometropic or strabismic amblyopia after refractive adaptation. Forty-six participants received chromatic light therapy and 42 received part-time patching. The chromatic group included amber-red (n = 16), yellow (n = 15), and orange (n = 15) subgroups. Outcomes were assessed at 4 weeks, 3 months, 5 months, 7 months, and 2 months after treatment cessation. Baseline-adjusted linear mixed-effects models were fitted using restricted maximum likelihood and an autoregressive AR(1) covariance structure. Fixed effects included follow-up visit, treatment group, the visit-by-treatment interaction, and the corresponding baseline outcome.

Results

BCVA improved over time in both groups. Adjusted BCVA changed from 0.458 to 0.261 logMAR with patching and from 0.446 to 0.246 logMAR with chromatic filters between 4 weeks and 7 months; the treatment-by-time interaction was not significant (p = .585). Treatment-by-time interactions were significant for contrast sensitivity and log10 stereopsis (both p < .001). From 3 months onward, the chromatic-filter group had higher adjusted contrast-sensitivity scores and lower, therefore better, stereopsis thresholds than the patching group. Within the chromatic-filter group, no filter-by-time interaction was detected for BCVA (p = .152), contrast sensitivity (p = .312), or stereopsis (p = .089). Most gains were maintained after treatment cessation.

Conclusion

All chromatic filters improved visual function, with benefits generally maintained after cessation. Yellow demonstrated an advantage over Orange for BCVA. Compared with patching, chromatic light therapy produced comparable BCVA improvement and superior contrast-sensitivity and stereopsis outcomes, supporting its potential as a non-invasive and patient-friendly treatment option for amblyopia.