January 5, 2026
By Kevin Chan, OD, MS, FAAO, IACMM
Photo Credit: Getty Images
Animal models have shown that visual inputs like light and optical defocus influence eye growth. It has also been well established that eye length, also known as axial length, naturally displays diurnal variations, typically peaking at midday and reaching its lowest point at midnight. Meanwhile, research has also found that both the timing and type of defocus, as well as light wavelength, impact these fluctuations. In particular, stronger inhibitory effects on axial elongation occurred when myopic defocus signals are coupled with blue light exposure.
Arguably, however, it also appeared to contradict with the current research and assumption that red light therapy halts myopia progression. In a clinical perspective, should repeated low-level red light (RLRL) therapy be used for patients with myopia progression? If so, under what wavelengths and for how long and how often? As you can see, ocular responses induced by wavelength-specific stimulus by red, blue, or violet light wavelengths remain controversial and inconclusive.
Study Objectives
Currently, no study has yet examined how the time of day interacts with different light wavelengths to affect ocular responses to defocus, which directly aids our understanding in refractive development and myopia progression. The study by Liu et al. explored the intricacies and examines how these variables influence ocular responses to defocus. Ultimately, the study aims to identify the most effective light exposure and timing strategies to optimize treatment outcomes.
Research Design
- Twenty healthy myopic adults (mean age ± SD: 25.9 ± 3.9 years)
- Refractive error by spherical equivalent: −4.12D ± 1.00D
- Duration and frequencies: One-hour visit; eight visits; alternating between morning (9:00–11:00 h) and afternoon (15:00–17:00 h) in eight non-consecutive days
- Measured variables:
- Extended-depth-of-focus (+2.25D myopic defocus) contact lens
- Single-vision contact lens (control)
- Light filters (blue-pass, red-pass and neutral density filters)
- Ocular measurements (before and after variable exposure):
- Axial length (AL)
- Choroidal thickness (CT)
- Melatonin level
Research Results
Axial elongation was shown to occur in the morning under all stimulated circumstances except with blue-pass filters. On the other hand, red-pass filters were found to elicit axial elongation in the afternoon only. Axial length changes in both time of day and the type of filters used were found to be statistically significant. Overall, the groups with blue-pass filters and optical defocus displayed the most potent protective effect against axial elongation (p = 0.04). Melatonin concentrations were found to be unaffected in absence of blue light exposure. In addition, choroidal thickness changes remained unchanged under all conditions.
Study Strengths and Limitations
The greatest strength of the study is the robust and rigorous study design for all the measured variables. It significantly helps minimize the impact of “noises” or confounding factors. Nevertheless, the study also underlies a few major limitations, including, yet not limited to:
- Subjects were not masked in each experimental condition.
- Short, acute duration of observation (one-hour exposure only), which may not be significant enough to draw generalization among different conditions for patients of all ages.
- Lacks longitudinal data to support if any cumulative effects of wavelength-specific light stimulus exist or sustain for months or years.
- Controlled light-induced experimental conditions may not necessarily reflect the real-world lighting environments among all different practical settings (e.g. windowed or windowless classrooms; type of light sources used –LED, incandescent; fluorescent; duration of exposure by natural light vs. digital device, etc.)
Clinical Significance and Implications
This study demonstrates the intricate relationships between the time-of-day and light wavelength exposure on axial length and melatonin level changes. Notably, the greatest inhibitory, thus the most protective response against axial elongation appeared to occur under blue-pass filters, in tandem with myopic defocus stimulus.
This study provides valuable insight into the dynamic nature of ocular physiology in response to environmental cues. In particular, the study showed that morning and afternoon exposure to the same combination of contact lenses and light wavelengths, surprisingly, resulted in opposite effects on axial length. This underscores the importance of treatment timing.
More importantly, the future direction likely lies in the integrated understanding of how to consider and incorporate light-based strategies with existing clinical interventions for myopia management to best optimize the clinical benefits for patients in real-world settings.
Abstract
Influence of Time-of-Day and Light Wavelengths on Ocular Responses to Defocus
Xiao Nicole Liu, Thomas John Naduvilath, Padmaja R. Sankaridurg
Purpose
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.
Methods
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).
Results
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.
Conclusions
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.
DOI: 10.1111/opo.70021
