Krupa Philip, BOptom, PhD
Brien Holden Vision Institute
Early onset of myopia leads to higher net myopia due to progression being faster at younger ages and more years spent in progression mode.1 The burden is significant with high myopia (greater than -5.00D) increasing the risk of complications such as glaucoma, cataract, retinal breaks and myopic maculopathy.
Therefore, it is important to prevent or delay the onset of myopia.
In considering risk factors for onset, both genetic and environmental factors were found to play a role.
In children, the odds of becoming myopic significantly increase when one or both parents are myopic.2-4 Additionally in those with parental myopia, the odds of myopia are nearly twice that in children with two myopic parents as compared to those with one myopic parent. 5
In children, the odds of becoming myopic significantly increase when one or both parents are myopic.2-4
Additionally in those with parental myopia, the odds of myopia are nearly twice that in children with two myopic parents as compared to those with one myopic parent.5
More near based activities
- Near work: Evidence indicates an association with odds of developing myopia increasing by 2% with every one diopter-hour more of near work per week.6 Near work activities included reading, use of computers and videogames. 6,7
- Early start of education: Early appearance of myopia in children living in Singapore compared to children living in Sydney, was attributed to an earlier start of education in Singapore.2
- Age: Children who were exposed to near work at a younger age (6 years or less) were more likely to develop myopia.8
Increased near work may lead to lag of accommodation or accommodative dysfunction which are considered to play a role in both onset and progression of myopia.
For example, there may be an accommodative lag during near based activities which results in hyperopic defocus, which may then serve as a signal for axial length elongation.
Less time outdoors and more time indoors
Children who spent more time outdoors were less likely to become myopic.9-11 Seasonal variations in ocular growth have been observed in children, with greater myopic shift and axial length elongation observed in winter months.12
The reason for time outdoors being protective for myopia is not entirely clear but increased light level is thought to play a role. For example, faster eye growth was observed in children exposed to light < 3000 lux and/or less than 40 minutes of outdoor activities per day.13
Moreover, exposure to outdoor light (sunlight) during school recess totaling 11.2 hours per week 14or exposure to light under trees or in hallways for 3.3 hours per day<sup>15</sup>was effective in reducing the incidence of myopia.
Dopamine, a hormone/ neurotransmitter released by the retinal amacrine cells when exposed to sunlight or bright light was reduced in animals with excessive ocular growth as a result of visual deprivation with diffusers.16
And when the diffusers were removed, dopamine levels increased and ocular growth reduced.17These observations suggest that increases in dopamine levels might inhibit eye growth.18
Urban versus rural living
Children from urban environments were likely to have twice the odds for myopia compared to those living in rural environments.19
High population density, constricted living space and housing type (living in apartments) were associated with an increased likelihood of myopia.20
Other factors reported to increase the likelihood of myopia were height, body mass index, birth season, intelligence and socioeconomic status.21
Children and young adults who spend greater time on near work, less time outdoors and more time indoors, are exposed to less ambient light in classrooms, have less exposure to sunlight and bright light, have an early start of education and live in urban spaces are at greater risk of becoming myopic.
In addition to these environmental risk factors, parental myopia could also predispose an individual to become myopic.
- Sankaridurg, P.R. and B.A. Holden, Practical applications to modify and control the development of ametropia. Eye (Lond), 2014. 28(2): p. 134-41.
- Rose, K.A., et al., Myopia, lifestyle, and schooling in students of Chinese ethnicity in Singapore and Sydney. Arch Ophthalmol, 2008a. 126(4): p. 527-30.
- You, Q.S., et al., Factors associated with myopia in school children in China: the Beijing childhood eye study. PLoS One, 2012. 7(12): p. e52668.
- Ahn, H., I.S. Lyu, and T.H. Rim, The Influence of Parental Myopia on Children’s Myopia in Different Generations of Parent-Offspring Pairs in South Korea. Semin Ophthalmol, 2018. 33(3): p. 419-428.
- Mutti, D.O., et al., Parental myopia, near work, school achievement, and children’s refractive error. Invest Ophthalmol Vis Sci, 2002. 43(12): p. 3633-40.
- Huang, H.M., D.S. Chang, and P.C. Wu, The Association between Near Work Activities and Myopia in Children-A Systematic Review and Meta-Analysis. PLoS One, 2015. 10(10): p. e0140419.
- Zadnik, K., et al., The effect of parental history of myopia on children’s eye size. JAMA, 1994. 271(17): p. 1323-7.
- Ma, Y., et al., Age-Specific Prevalence of Visual Impairment and Refractive Error in Children Aged 3-10 Years in Shanghai, China. Invest Ophthalmol Vis Sci, 2016. 57(14): p. 6188-6196.
- French, A.N., et al., Time outdoors and the prevention of myopia. Exp Eye Res, 2013. 114: p. 58-68.
- He, M., et al., Effect of Time Spent Outdoors at School on the Development of Myopia Among Children in China: A Randomized Clinical Trial. JAMA, 2015. 314(11): p. 1142-8.
- Ip, J.M., et al., Myopia and the urban environment: findings in a sample of 12-year-old Australian school children. Invest Ophthalmol Vis Sci, 2008. 49(9): p. 3858-63.
- Donovan, L., et al., Myopia progression in Chinese children is slower in summer than in winter. Optom Vis Sci, 2012. 89(8): p. 1196-202.
- Read, S.A., M.J. Collins, and S.J. Vincent, Light Exposure and Eye Growth in Childhood. Invest Ophthalmol Vis Sci, 2015. 56(11): p. 6779-87.
- Wu, P.C., et al., Outdoor activity during class recess reduces myopia onset and progression in school children. Ophthalmology, 2013. 120(5): p. 1080-5.
- Wu, P.C., et al., Myopia Prevention and Outdoor Light Intensity in a School-Based Cluster Randomized Trial. Ophthalmology, 2018. 125(8): p. 1239-1250.
- Dong, F., et al., Inhibition of experimental myopia by a dopamine agonist: different effectiveness between form deprivation and hyperopic defocus in guinea pigs. Mol Vis, 2011. 17: p. 2824-34.
- Pendrak, K., et al., Retinal dopamine in the recovery from experimental myopia. Curr Eye Res, 1997. 16(2): p. 152-7.
- Feldkaemper, M. and F. Schaeffel, An updated view on the role of dopamine in myopia. Exp Eye Res, 2013. 114: p. 106-19.
- Rudnicka, A.R., et al., Global variations and time trends in the prevalence of childhood myopia, a systematic review and quantitative meta-analysis: implications for aetiology and early prevention. Br J Ophthalmol, 2016. 100(7): p. 882-890.
- Wu, X., et al., Housing type and myopia: the mediating role of parental myopia. BMC Ophthalmol, 2016. 16(1): p. 151.
- Wolffsohn, J.S., et al., IMI – Myopia Control Reports Overview and Introduction. Invest Ophthalmol Vis Sci, 2019. 60(3): p. M1-M19.