Influence of time-of-day and light wavelengths on ocular responses to defocus

This study explored potential effects of time of day and light filters on the ocular response to 1-h myopic defocus and associated changes in melatonin.

Twenty healthy myopic adults (mean age ± SD: 25.9 ± 3.9 years; spherical equivalent: -4.12 ± 1.00 D) participated in this study. Eight 1-h visits, alternating between morning (9:00-11:00 h) and afternoon (15:00-17:00 h) were randomly scheduled on eight non-consecutive days. Ocular measurements (axial length and choroidal thickness) of the right eye were taken at both the beginning and the end of each visit, following saliva sample collection for melatonin assessment. Two contact lenses were compared: single vision (control) and extended-depth-of-focus (+2.25 D myopic defocus), in combination with three sets of light filters (blue-pass, red-pass and neutral density filters).

Axial length elongated in the morning under three of the four conditions, with blue-pass filters being the exception; no significant changes were detected in the afternoon except for the elongation with red-pass filters. Both time of day and filters demonstrated significant effects on 1-h axial length change (both p < 0.001; interaction of filter and timing, p < 0.001). The combination of blue-pass filters and defocus showed an overall significant protective effect against axial elongation (p = 0.04). Melatonin concentration was influenced by time (p = 0.01), with concentration levels decreasing in the morning with neutral density and blue-pass filters but remaining unchanged in the absence of blue light (with red-pass filters). Choroidal thickness changes were not significant across all conditions.

This study demonstrates the impact of time-of-day and wavelength-specific light exposure on axial length changes and melatonin levels. The protective effect of blue-pass filters combined with myopic defocus highlights the potential of spectral light manipulation for myopia control. Further research is needed to investigate long-term effects and validate these findings in real-world settings.