Myopia and its vision-threatening complications present a global public health challenge (1-3). The most important and consistently established modifiable environmental risk factor for myopia development is insufficient outdoor time (4, 5). In some regions, this evidence has already been translated into public health initiatives and clinical recommendations, with increased outdoor time promoted for both primary prevention and myopia control. Understanding how light influences ocular growth has become one of the most active areas of myopia research. Alongside the well-established benefits of outdoor exposure, several novel light-based interventions are now entering clinical practice or clinical trials.
The benefits of outdoor light
A consistent finding in myopia research is that children who spend more time outdoors are less likely to develop myopia (6-8). The evidence is strongest for delaying or preventing myopia onset, while the effect on slowing myopia progression appears modest (7, 8). Clinically, this means encouraging outdoor time early, ideally before myopia develops, rather than only after diagnosis.
Outdoor environments differ from indoor environments in several ways (9):
Substantially higher light intensity
Broader spectral composition
Greater visual complexity, including richer contrast, longer viewing distances, and variable luminance
Bright light may protect against myopia through multiple mechanisms, including retinal dopamine signalling and circadian regulation, both of which are increasingly recognized as relevant to axial eye growth (10). Emerging research also suggests that biologically effective light, quantified using melanopic equivalent daylight illuminance (mEDI), may provide a more physiologically meaningful measure of ocular and circadian light exposure than conventional photopic illuminance, although its role in myopia development and progression remains under investigation (11). Exposure above approximately 1,000 lux has been proposed as a biologically meaningful threshold for protection against myopia (12). This level is readily achieved outdoors, even in shade or cloudy conditions, but is usually well above typical indoor lighting levels of 100–500 lux.
Timing of light exposure
There is growing interest in whether the timing of light exposure matters for myopia. Observational studies have linked nighttime light exposure with myopia (13). Myopic children have also been reported to spend less time in very dim light (<1 lux) and bright outdoor light (>1,000 lux), and more time in dim-to-moderate light (1–30 lux), particularly in the evening (14). Although these findings do not prove causality, they are consistent with broader evidence that regular exposure to bright days and dark nights supports general health (15).
Emerging light-based interventions
Brighter indoor environments are a promising light-based approach. High-illuminance, broad-spectrum classroom lighting has been associated with reduced myopia incidence and slower progression (16). Daylight-enhancing classroom designs, such as transparent walls to increase indoor light levels, have also been explored, although studies have not been designed to assess myopia outcomes (17). However, even very bright classrooms rarely reproduce the intensity, spectral composition, or dynamic visual environment of outdoor settings. These strategies may thus support daytime light exposure, but they cannot replace outdoor time and must be weighed against glare, discomfort, heat load, cost, energy use, and feasibility.
Repeated low-level red-light therapy (RLRL) is a widely discussed device-based treatment. Although devices vary, treatment typically involves brief repeated exposure to red light. Recent meta-analyses of randomized controlled trials reported substantial reductions in axial elongation and refractive progression (18, 19). However, safety concerns remain. In clinical trials, RLRL has generally been well tolerated, with transient afterimages lasting several minutes being the most commonly reported visual symptom (20). Although uncommon, retinal structural changes have also been reported in treated children, including foveal outer retinal changes, reduced cone density, small cystoid abnormalities, and hypoautofluorescent plaques with ellipsoid zone disruption (21-23). Although these findings resolved after treatment cessation, they underscore the need for careful device regulation and longer-term safety follow-up. Overall, RLRL is a promising intervention, but it should be used cautiously, with careful patient selection and monitoring.
Wavelength-specific therapies remain at an early stage of clinical development. A key challenge is distinguishing true wavelength-specific effects from those attributable to increased overall retinal illumination. Among the emerging approaches, a recent smartphone-based selective blue-light stimulation system showed similar six-month efficacy outcomes to DIMS spectacles and was reported to be safe and well-tolerated (24). Violet-light-transmitting spectacle lenses have been studied for longer, but clinical trials have shown only modest effects on axial elongation (25). Other wavelength-specific therapies, including indigo-light systems, are also under investigation and may provide further insight into the role of spectral composition in ocular growth (26). However, larger independent clinical trials with longer follow-up are needed before any of these approaches can be recommended for routine clinical practice.
Limitations of the current evidence
Several limitations should temper the interpretation of the current evidence. Many intervention studies, particularly those investigating RLRL and some school-based approaches, have been conducted in East Asian populations, and their findings may not generalize directly to other populations or clinical settings.
Studies also vary in how light exposure is measured, ranging from questionnaires to wearable sensors, making direct comparison difficult. In addition, long-term safety data for newer device-based light therapies remain limited, and several spectral approaches still lack large, independent randomized clinical trials.
These limitations do not weaken the recommendation for outdoor time, but they support caution when adopting newer light-based therapies into routine clinical care.
Practical clinical recommendations
In summary, the strongest evidence and most practical recommendation is to increase time spent outdoors. A pragmatic clinical target is approximately two hours of outdoor time overall per day (12). This should be framed as a routine behavior, and families should be reassured that the goal is simply to spend time outside in daylight, not to seek direct sun exposure. Sun and UV protection, including hats, sunglasses, and sunscreen, should be recommended, particularly in high-UV conditions.
Clinicians should be clear about the aim of the recommendation. For a young child who is not yet myopic, outdoor time is a primary prevention strategy. For a child who is already myopic, outdoor time remains advisable for general health, and may provide some support for slowing myopia progression, but should not be presented as a substitute for established myopia-control interventions.
Families should be encouraged to build outdoor exposure into their daily routines through school breaks, active travel, outdoor play, and weekend activities. This advice is especially relevant for younger children, siblings of myopic children, and children with other risk factors. It aligns with broader child health goals, including physical activity, sleep, mood, and general well-being. Clinicians can reinforce these messages during routine consultations, helping families translate the evidence into sustainable everyday behaviors.
Public health implementation
Outdoor time should not depend solely on individual families, and public health strategies are needed, including awareness campaigns and changes to educational settings that promote regular daylight exposure. Small but meaningful measures, such as outdoor breaks, walking or cycling to school, shaded playgrounds, and outdoor lessons, are important. Several Asian countries, including Taiwan, Singapore, and China, have already successfully implemented national myopia management programs that incorporate elements of these strategies.
Conclusion
Light therapies are part of myopia prevention and myopia control, but not all light-based approaches are at the same stage of evidence. Increased outdoor time remains the strongest, safest, and most practical recommendation, particularly for preventing myopia onset. A practical clinical target is around two hours of outdoor time per day. Brighter indoor environments may provide additional support. RLRL shows promise for myopia control, but safety, device standards, and generalizability require continued scrutiny. As the evidence evolves, clinicians should continue to prioritize interventions supported by robust clinical trials while remaining appropriately cautious about newer technologies whose long-term safety has yet to be established.
References
- BA Holden et al., “Global Prevalence of Myopia and High Myopia and Temporal Trends From 2000 Through 2050,” Ophthalmology, 123, 1036 (2016).
- AEG Haarman et al., “The Complications of Myopia: A Review and Meta-Analysis,” Invest Ophthalmol Vis Sci, 61, 49 (2020).
- JWL Tideman et al., “Association of Axial Length With Risk of Uncorrectable Visual Impairment for Europeans With Myopia,” JAMA Ophthalmol, 134, 1355 (2016).
- KA Rose et al., “Outdoor Activity Reduces the Prevalence of Myopia in Children,” Ophthalmology, 115, 1279 (2008).
- IG Morgan et al., “IMI Risk Factors for Myopia,” Invest Ophthalmol Vis Sci, 62, 3 (2021).
- S Xiong et al., “Time Spent in Outdoor Activities in Relation to Myopia Prevention and Control: A Meta-Analysis and Systematic Review,” Acta Ophthalmol, 95, 551 (2017).
- K Cao et al., “Significance of Outdoor Time for Myopia Prevention: A Systematic Review and Meta-Analysis Based on Randomized Controlled Trials,” Ophthalmic Res, 63, 97 (2020).
- D Li et al., “Is Spending More Time Outdoors Able to Prevent and Control Myopia in Children and Adolescents? A Meta-Analysis,” Ophthalmic Res, 67, 393 (2024).
- G Lingham et al., “How Does Spending Time Outdoors Protect Against Myopia? A Review,” Br J Ophthalmol, 104, 593 (2020).
- X Zhou et al., “Dopamine Signaling and Myopia Development: What Are the Key Challenges,” Prog Retin Eye Res, 61, 60 (2017). DOI: 10.1016/j.preteyeres.2017.06.003.
- LJM Schlangen, LLA Price, “The Lighting Environment, Its Metrology, and Non-Visual Responses,” Front Neurol, 12 (2021).
- PC Wu et al., “Increased Time Outdoors Is Followed by Reversal of the Long-Term Trend to Reduced Visual Acuity in Taiwan Primary School Students,” Ophthalmology, 127, 1462 (2020).
- GE Quinn et al., “Myopia and Ambient Lighting at Night,” Nature, 399, 113 (1999).
- EG Landis et al., “Dim Light Exposure and Myopia in Children,” Invest Ophthalmol Vis Sci, 59, 4804 (2018).
- DP Windred et al., “Brighter Nights and Darker Days Predict Higher Mortality Risk: A Prospective Analysis of Personal Light Exposure in >88,000 Individuals,” Proc Natl Acad Sci U S A, 121, e2405924121 (2024).
- HM Cai et al., “Effect of Artificial Natural Light on the Development of Myopia Among Primary School-Age Children in China: A Three-Year Longitudinal Study,” Int J Ophthalmol, 17, 924 (2024).
- Z Zhou et al., “Pilot Study of a Novel Classroom Designed to Prevent Myopia by Increasing Children’s Exposure to Outdoor Light,” PLoS One, 12, e0181772 (2017).
- MA Youssef et al., “Efficacy of Repeated Low-Level Red Light (RLRL) Therapy on Myopia Outcomes in Children: A Systematic Review and Meta-Analysis,” BMC Ophthalmol, 24, 78 (2024).
- D Liu et al., “Efficacy of Repeated Low-Level Red-Light Therapy for Myopia Management in Children and Adolescents: A Systematic Review and Meta-Analysis,” BMC Ophthalmol, 26, 139 (2026).
- Y Chen et al., “Safety of Repeated Low-Level Red-Light Therapy for Myopia: A Systematic Review,” Asia Pac J Ophthalmol, 13, 100124 (2024).
- Z Zhang et al., “Structural OCT Changes Following Repeated Low-Level Red-Light Therapy for Myopia Prevention,” JAMA Ophthalmol, 143, 876 (2025).
- X Liao et al., “Cone Density Changes After Repeated Low-Level Red Light Treatment in Children With Myopia,” JAMA Ophthalmol, 143, 480 (2025).
- H Liu et al., “Retinal Damage After Repeated Low-Level Red-Light Laser Exposure,” JAMA Ophthalmol, 141, 693 (2023).
- J Loughman et al., “MyopiaX-1 Safety and Efficacy of a Novel Approach to Slow Juvenile Myopia Progression: A Multicenter, Randomized, Controlled Trial,” Ophthalmol Sci, 6, 100973 (2026).
- K Mori et al., “Effect of Violet Light-Transmitting Eyeglasses on Axial Elongation in Myopic Children: A Randomized Controlled Trial,” J Clin Med, 10, 5462 (2021).
- R Grytz et al., “The µ-Opic: A Metric for Assessing Violet-Indigo-Blue Light for Myopia Suppression,” Invest Ophthalmol Vis Sci, 66, 949 (2025).
