WHETHER DUE TO demanding academic requirements, excessive digital device use, or even quarantining, many children in industrialized nations today spend most of their time indoors. What does this reduced exposure to natural outdoor lighting mean for myopia?

OUTDOOR TIME

Many researchers have attempted to quantify the effects of time spent outdoors on myopia, with meta-analysis of relevant studies generating a broad consensus that there is reduced incidence of myopia in children who spend more time outdoors (Wu et al, 2018; Xiong et al, 2017). Children who spend less than 13 hours per week outdoors are at the greatest risk for developing myopia (Xiong et al, 2017). While the relationship between outdoor time and the rate of myopia progression is less clear, myopia progression has been shown to be slower during summer months, when children often spend more time outdoors (Fulk et al, 2002).

LIGHTING CHARACTERISTICS

Possible explanations for the beneficial effects of increased outdoor time include the differences in brightness and spectral distribution of light encountered in outdoor versus indoor environments. On average, outdoor lighting is 10 to 1,000 times brighter and significantly broader spectrum than indoor environments, which are often illuminated with LED, fluorescent, or incandescent sources (Dharani et al, 2012).

Higher-intensity light (whether sunlight or artificial light) has been shown to counteract induced myopia in animal models, from chicks to Rhesus monkeys (Ashby and Schaeffel, 2010; Karouta and Ashby, 2014; Smith et al, 2012; Wang et al, 2015). The relationship between the spectral composition of light and myopia is more complicated and may involve the effects of longitudinal chromatic aberration or direct induction of biological pathways that influence eye growth (Zhang and Zhu, 2022). While monochromatic blue light has been shown to inhibit myopia in chicks and guinea pigs, contrasting results have been observed in tree shrews and monkeys (Rucker and Wallman, 2008; Liu et al, 2011; Gawne et al, 2017; Smith et al, 2015).

TREATMENT IMPLICATIONS

Perhaps the simplest conclusion to be drawn from the existing literature on the role of lighting on myopia is that clinicians should be encouraging all young patients to spend as much time as possible outdoors, with a target minimum of 13 hours per week. As knowledge of the effects of light on myopia continues to grow, clinicians may ultimately find that optimizing the brightness and/or spectral distribution of retinal illuminance may be as important as peripheral hyperopia in combatting myopic eye growth.

Novel treatments that seek to slow myopia progression via modified retinal illumination, including repeated low-level red light (RLRL), violet light-emitting spectacles, and active illumination spectacles, are the subject of ongoing research. RLRL treatment involves exposure to several minutes of bright 650nm light twice per day and has been shown to significantly slow myopia progression over a period of up to two years (Xiong et al, 2022).

Violet light-emitting spectacles incorporate lenses that transmit wavelengths from 360nm to 400nm, which are blocked by standard ophthalmic lenses. In a recent study, a modest treatment effect was observed in a subgroup analysis of 8- to 10-year-olds using the technology (Torii et al, 2022).

Active illumination spectacles are electronic glasses that incorporate modified retinal illumination in addition to peripheral defocus. Results of a pilot study were presented at the 2022 International Myopia Conference and demonstrated a robust treatment effect in 11 children who wore an active illumination device for 90 minutes, five days per week (Kubota, 2022). CLS

References

1. Wu PC, Chen CT, Lin KK, et al. Myopia Prevention and Outdoor Light Intensity in a School-Based Cluster Randomized Trial. Ophthalmology. 2018 Aug;125:1239-1250.
2. Xiong S, Sankaridurg P, Naduvilath T, et al. Time spent in outdoor activities in relation to myopia prevention and control: a meta-analysis and systematic review. Acta Ophthalmol. 2017 Sep;95:551-566.
3. Fulk GW, Cyert LA, Parker DA. Seasonal variation in myopia progression and ocular elongation. Optom Vis Sci. 2002 Jan;79:46-51.
4. Dharani R, Lee CF, Theng ZX, et al. Comparison of measurements of time outdoors and light levels as risk factors for myopia in young Singapore children. Eye (Lond). 2012 Jul;26:911-918.
5. Ashby RS, Schaeffel F. The Effect of Bright Light on Lens Compensation in Chicks. Invest Ophthalmol Vis Sci. 2010 Oct;51:5247-5253.
6. Karouta C, Ashby RS. Correlation Between Light Levels and the Development of Deprivation Myopia. Invest Ophthalmol Vis Sci. 2014 Dec;56:299-309.
7. Smith EL 3rd, Hung LF, Huang J. Protective Effects of High Ambient Lighting on the Development of Form-Deprivation Myopia in Rhesus Monkeys. Invest Ophthalmol Vis Sci. 2012 Jan;53:421-428.
8. Wang Y, Ding H, Stell WK, et al. Exposure to Sunlight Reduces the Risk of Myopia in Rhesus Monkeys. PLoS ONE. 2015 Jun 1;10:e0127863.
9. Zhang P, Zhu H. Light Signaling and Myopia Development: A Review. Ophthalmol Ther. 2022 Jun;11:939-957.
10. Rucker FJ, Wallman J. Cone signals for spectacle-lens compensation: differential responses to short and long wavelengths. Vision Res. 2008 Sep;48:1980-1991.
11. Liu R, Qian YF, He JC, et al. Effects of different monochromatic lights on refractive development and eye growth in guinea pigs. Exp Eye Res. 2011 Jun;92:447-553.
12. Gawne TJ, Siegwart JT Jr, Ward AH, Norton TT. The wavelength composition and temporal modulation of ambient lighting strongly affect refractive development in young tree shrews. Exp Eye Res. 2017 Feb;155:75-84.
13. Smith EL 3rd, Hung LF, Arumugam B, Holden BA, Neitz M, Neitz J. Effects of long-wavelength lighting on refractive development in infant rhesus monkeys. Invest Ophthalmol Vis Sci. 2015 Oct;56:6490-6500.
14. Xiong R, Zhu, Z, Jiang Y, et al. Sustained and rebound effect of repeated low-level red-light therapy on myopia control: A 2-year post-trial follow-up study. Clin Exp Ophthalmol. 2022 Dec;50:1013-1024.
15. Torii H, Mori K, Okano T, et al. Short-Term Exposure to Violet Light Emitted from Eyeglass Frames in Myopic Children: A Randomized Pilot Clinical Trial. J Clin Med. 2022 Oct;11:6000.
16. Kubota R, Joshi N, Samandarova I, et al. Biometric changes associated with active stimulation of the peripheral retina with myopically defocused images in humans. Abstract from International Myopia Conference; 2022 Sep 4-7; Rotterdam, Netherlands.