June 1, 2023
By Zeeshan Akhtar, BOptom, MPhil, PhD Candidate at Brien Holden Vision Institute
There is a growing body of research investigating risk factors that are influential in the development and progression of myopia in children and adolescents. The factors that have been identified include genetics, engagement in outdoor activities, near work, and the intensity and spectral composition of light. As research evidence in this area continues to evolve, it is vital to understand how the findings can influence the advice given in clinical practice.
Genetic Factors Are Only Part of the Story
Parental myopia has been associated with myopia incidence in children.1 More than 25 genetic myopia loci have been identified so far using genome-wide association studies. However, the results vary across ethnicities.2 It has been reported that there is an interplay of genetic factors with environmental stresses in myopia pathogenesis.3 Therefore, it is evident that genetics alone cannot explain the rapid increase in global myopia onset and prevalence.
Impact of Time Spent Outdoors on Myopia
Environmental factors, including outdoor lighting, have been shown to influence the onset and progression of myopia. Interventional studies provide convincing evidence that spending time outdoors in natural light has a protective effect and can delay the onset of myopia.4,5 However, the exact threshold duration of outdoor light exposure required to prevent myopia is still unknown.
Furthermore, research suggests that outdoor light exposure may also slow down myopia progression in already myopic eyes.6,7,8 A meta-analysis of six interventional studies reported that increased outdoor time exposure could reduce ocular elongation in myopic eyes by 0.15 mm/year compared to control eyes.8 However, due to data scarcity, there is still no strong consensus among researchers as to whether the increased outdoor time is solely preventative or can also help slow down the progression of myopia.
The protective effect of spending time outdoors may be associated with a uniform viewing environment that reduces peripheral defocus and/or exposure to sunlight characteristics such as intensity and spectral composition.9,10 Animal models have provided insights into the effects of different light wavelengths on ocular growth. For example, exposure to ultraviolet (UV) light has been found to induce hyperopia in chickens,11 whereas tree shrews12 and rhesus monkeys12 reared with red light exhibited reduced ocular elongation.
In humans, red-light therapy for controlling myopia has gained increasing attention among researchers and stakeholders. Preliminary studies have shown the potential of red-light therapy in controlling myopia progression.14,15 However, the long-term safety and efficacy of this therapy are yet to be clearly established.
Near Work and Digital Device Use in Myopia
The use of digital devices and prolonged screen time have been extensively studied in relation to myopia onset and progression. Several studies have reported that myopes tend to have greater screen time than emmetropes even before myopia’s onset.16 Additionally, evidence suggests an association between myopia and data usage.17 However, it is important to note that the current body of research does not provide clear evidence of a causal relationship between digital screen time and myopia.18 Further research utilizing objective measures of screen time and its association with myopia is necessary to strengthen the findings and establish a clearer understanding of the relationship.
On the other hand, near work has been consistently shown to be associated with myopia onset and progression. Myopes tend to engage in near work at a shorter distance than non-myopes and spend more time performing near activities.19 Despite the available research in this area, researchers who have undertaken systematic reviews and meta-analyses of available data believe there is still further work to do in this area. Research could be strengthened by more longitudinal studies and better objective verification of near-viewing behavior, including the use of digital devices.20
- Genetic factors have an interaction with environmental factors in myopia development.
- Spending time outdoors has a protective effect on myopia onset and may slow its progression.
- Different wavelengths of light can affect ocular growth differently.
- Red light therapy has the potential to slow myopia progression.
- The impact of digital device uses and near work on myopia onset and progression is yet to be established.
|Zeeshan Akhtar (B.Optom, M.Phil) is a PhD Candidate at Brien Holden Vision Institute supervised by Dr. Arthur Back and Dr. Arthur Ho.|
- Tedja, M. S., Haarman, A. E., Meester-Smoor, M. A., Kaprio, J., Mackey, D. A., Guggenheim, J. A., … & CREAM Consortium. (2019). IMI–myopia genetics report. Investigative ophthalmology & visual science, 60(3), M89-M105.
- Wang, Y. M., Lu, S. Y., Zhang, X. J., Chen, L. J., Pang, C. P., & Yam, J. C. (2022). Myopia genetics and heredity. Children, 9(3), 382.
- Cai, X. B., Shen, S. R., Chen, D. F., Zhang, Q., & Jin, Z. B. (2019). An overview of myopia genetics. Experimental eye research, 188, 107778.
- Sherwin, J. C., Reacher, M. H., Keogh, R. H., Khawaja, A. P., Mackey, D. A., & Foster, P. J. (2012). The association between time spent outdoors and myopia in children and adolescents: a systematic review and meta-analysis. Ophthalmology, 119(10), 2141-2151.
- Xiong, S., Sankaridurg, P., Naduvilath, T., Zang, J., Zou, H., Zhu, J., … & Xu, X. (2017). Time spent in outdoor activities in relation to myopia prevention and control: a meta‐analysis and systematic review. Acta ophthalmologica, 95(6), 551-566.
- Wu, P. C., Tsai, C. L., Wu, H. L., Yang, Y. H., & Kuo, H. K. (2013). Outdoor activity during class recess reduces myopia onset and progression in school children. Ophthalmology, 120(5), 1080-1085.
- Jin, J. X., Hua, W. J., Jiang, X., Wu, X. Y., Yang, J. W., Gao, G. P., … & Tao, F. B. (2015). Effect of outdoor activity on myopia onset and progression in school-aged children in northeast China: The Sujiatun Eye Care Study. BMC ophthalmology, 15, 1-11.
- Ho, C. L., Wu, W. F., & Liou, Y. M. (2019). Dose–response relationship of outdoor exposure and myopia indicators: a systematic review and meta-analysis of various research methods. International journal of environmental research and public health, 16(14), 2595.
- Muralidharan, A. R., Lança, C., Biswas, S., Barathi, V. A., Wan Yu Shermaine, L., Seang-Mei, S., … & Najjar, R. P. (2021). Light and myopia: from epidemiological studies to neurobiological mechanisms. Therapeutic advances in ophthalmology, 13, 25158414211059246.
- Jonas, J. B., Ang, M., Cho, P., Guggenheim, J. A., He, M. G., Jong, M., … & Wolffsohn, J. S. (2021). IMI prevention of myopia and its progression. Investigative ophthalmology & visual science, 62(5), 6-6.
- Rucker, F. J., & Wallman, J. (2009). Chick eyes compensate for chromatic simulations of hyperopic and myopic defocus: evidence that the eye uses longitudinal chromatic aberration to guide eye growth. Vision research, 49(14), 1775-1783.
- Gawne, T. J., Siegwart Jr, J. T., Ward, A. H., & Norton, T. T. (2017). The wavelength composition and temporal modulation of ambient lighting strongly affect refractive development in young tree shrews. Experimental eye research, 155, 75-84.
- Smith, E. L., Hung, L. F., Arumugam, B., Holden, B. A., Neitz, M., & Neitz, J. (2015). Effects of long-wavelength lighting on refractive development in infant rhesus monkeys. Investigative ophthalmology & visual science, 56(11), 6490-6500.
- Jiang, Y., Zhu, Z., Tan, X., Kong, X., Zhong, H., Zhang, J., … & He, M. (2022). Effect of repeated low-level red-light therapy for myopia control in children: a multicenter randomized controlled trial. Ophthalmology, 129(5), 509-519.
- Dong, J., Zhu, Z., Xu, H., & He, M. (2023). Myopia control effect of repeated low-level red-light therapy in Chinese children: a randomized, double-blind, controlled clinical trial. Ophthalmology, 130(2), 198-204.
- Lanca, C., & Saw, S. M. (2020). The association between digital screen time and myopia: A systematic review. Ophthalmic and Physiological Optics, 40(2), 216-229.
- McCrann, S., Loughman, J., Butler, J. S., Paudel, N., & Flitcroft, D. I. (2021). Smartphone use as a possible risk factor for myopia. Clinical and Experimental Optometry, 104(1), 35-41.
- Foreman, J., Salim, A. T., Praveen, A., Fonseka, D., Ting, D. S. W., He, M. G., … & Dirani, M. (2021). Association between digital smart device use and myopia: a systematic review and meta-analysis. The Lancet Digital Health, 3(12), e806-e818.
- Wen, L., Cao, Y., Cheng, Q., Li, X., Pan, L., Li, L., … & Yang, Z. (2020). Objectively measured near work, outdoor exposure and myopia in children. British Journal of Ophthalmology, 104(11), 1542-1547.
- Gajjar, S., & Ostrin, L. A. (2022). A systematic review of near work and myopia: measurement, relationships, mechanisms and clinical corollaries. Acta Ophthalmologica, 100(4), 376-387.