December 1, 2022
By Nicole Liu, MOptom, PhD Candidate, Brien Holden Vision Institute
Seasonal variations in myopia progression have been frequently reported across regions, age, and ethnic groups, consistently revealing greater growth during winter months compared to summer. Although there is still a debate on whether findings from those studies support protective effects of outdoor light exposure on myopia progression, it is well accepted that those seasonal differences can be attributed to varied individual light exposure patterns affected by seasonal daylight changes and therefore altered lifestyles or behaviors.1-5
Remarkably, in addition to light intensity and the number of hours of daylight, the spectral composition of light varies considerably between seasons. For instance, during the summer, a significantly greater portion of blue light was detected in evening hours compared to the winter.6 Blue light is of particular interest to recent myopia research due to a unique spectral sensitivity toward blue light (~484 nm) of the intrinsically photosensitive retinal ganglion cells (ipRGCs). These ipRGCs serve as a crucial messenger for regulating our circadian rhythms via direct communication with the “master clock,” a pacemaker in the hypothalamus called the suprachiasmatic nucleus (SCN).7 Meanwhile, the latest findings from animal models of myopia and genome wide association studies suggest the involvement of the circadian clock in myopia.8,9 Therefore, it would be exciting to investigate if seasonal changes observed in the blue component of daylight contributed to differences in myopia progression between seasons and whether circadian rhythm plays a role in the process.
To conclude, in reviewing the work by Gwiazda et al.,2 and considering the most recent findings on associations of the circadian clock with myopia, new research ideas have provoked alternative explanations of why there is a relatively slow myopia growth rate during summertime.
Seasonal Variations in the Progression of Myopia in Children Enrolled in the Correction of Myopia Evaluation Trial
Jane Gwiazda, Li Deng, Ruth Manny, and Thomas T. Norton for the COMET Study Group
Purpose: To investigate monthly and seasonal variations in the progression of myopia in children enrolled in the Correction of Myopia Evaluation Trial (COMET).
Methods: An ethnically diverse cohort of 469 myopic 6- to <12-year-old children was randomized to single vision or progressive addition lenses and followed for 3 years with 98.5% retention. Progression of myopia was measured semiannually by noncycloplegic autorefraction (Nidek ARK 700A) and annually by cycloplegic autorefraction, with the former measurements used in these analyses. The semiannual progression rate was calculated as (change in spherical equivalent refraction between two consecutive semiannual visits/number of days between the two visits) times 182.5. Months were categorized as the midpoint between two visit dates. Seasons were classified as winter (October through March) or summer (April through September). The seasonal difference was tested using a linear mixed model adjusting for demographic variables (age, sex, ethnicity), baseline refraction, and treatment group.
Results: Data from 358 children (mean [± SD] age = 9.84 ± 1.27 years; mean myopia = -2.54 ± 0.84 diopters [D]) met the criteria for these analyses. Myopia progression varied systematically by month; it was slower in April through September than in the other months. Mean progression in winter was -0.35 ± 0.34 D and in summer was -0.14 ± 0.32 D, a statistically significant difference (0.21 D, P < 0.0001). The same seasonal pattern was found by age, sex, ethnicity (except in the small sample of Asians), lens type, and clinical center.
Conclusions: The slower progression of myopia found in summer is likely related to children’s spending more time outdoors and fewer hours in school. The data have clinical implications regarding the time of year and the frequency with which myopic children have eye examinations and the need for precise timing of visits in clinical trials testing new myopia treatments. (ClinicalTrials.gov number, NCT00000113.).
Gwiazda, J., Deng, L., Manny, R., & Norton, T. T. (2014). Seasonal variations in the progression of myopia in children enrolled in the correction of myopia evaluation trial. Investigative Ophthalmology & Visual Science, 55(2), 752-758.
|Xiao (Nicole) Liu is a current PhD candidate at UNSW School of Optometry and Vision Science and Brien Holden Vision Institute, under the supervision of Professor Padmaja Sankaridurg and Associate Professor Thomas John Naduvilath. Dr. Liu received her Bachelor of Clinical Medicine (Optometry and Ophthalmology) from Tianjin Medical University in China before obtaining her Master of Optometry degree in 2012 at UNSW. After working as a clinical research optometrist for a few years, she decided to pursue a PhD degree in optometry. She has been awarded the inaugural Dr. David Wilson Memorial Scholarship for her PhD. She was also awarded the ARVO Travel Grant and the ISCLR Student Abstract Grant in 2022 for her research on myopia and circadian rhythm.|
- Donovan, L., et al., Myopia progression in Chinese children is slower in summer than in winter. Optometry and vision science : official publication of the American Academy of Optometry, 2012. 89(8): p. 1196-1202.
- Gwiazda, J., et al., Seasonal variations in the progression of myopia in children enrolled in the correction of myopia evaluation trial. Invest Ophthalmol Vis Sci, 2014. 55(2): p. 752-8.
- Ulaganathan, S., et al., Influence of seasons upon personal light exposure and longitudinal axial length changes in young adults. Acta Ophthalmol, 2018.
- Cui, D., K. Trier, and S. Munk Ribel-Madsen, Effect of day length on eye growth, myopia progression, and change of corneal power in myopic children. Ophthalmology, 2013. 120(5): p. 1074-9.
- Morgan, I.G., et al., IMI Risk Factors for Myopia. Invest Ophthalmol Vis Sci, 2021. 62(5): p. 3.
- Thorne, H.C., et al., Daily and seasonal variation in the spectral composition of light exposure in humans. Chronobiol Int, 2009. 26(5): p. 854-66.
- Berson, D.M., Strange vision: ganglion cells as circadian photoreceptors. Trends Neurosci, 2003. 26(6): p. 314-20.
- Stone, R.A., et al., Altered ocular parameters from circadian clock gene disruptions. PLOS ONE, 2019. 14(6): p. e0217111.
- Hysi, P.G., et al., Meta-analysis of 542,934 subjects of European ancestry identifies new genes and mechanisms predisposing to refractive error and myopia. Nat Genet, 2020. 52(4): p. 401-407.