According to the International Myopia Institute (IMI) Defining and Classifying Myopia report,1 pre-myopia is defined as a refractive state of an eye between +0.75 and more than -0.50D in children where a combination of baseline refraction, age, and other quantifiable risk factors provides a sufficient likelihood of the future development of myopia to merit preventative interventions. Here is a case shared by PC with the Myopia Profile community that involves a child who fits the definition of a pre-myope.
What features define a pre-myope?
Here is a checklist of risks for pre-myopia and/or myopia development, with the last highlighted as the key risk factor defining pre-myopia, independent of the others.2
- Age (5-9 years old)
- Asian ethnicity
- Parental myopia
- Binocular vision disorders
- Insufficient outdoor time
- Excessive time spent on near work
- Refractive error (Being less than +0.75D at age 6-7)
This child is clearly a pre-myope because he is 5 years of age and with not enough age normal hyperopia - only R +0.75 L +0.50. The family history of myopia is clear; binocular vision and outdoor / near work time risk factors aren't described. You can read more about How to identify and manage pre-myopes via the link.
Another concerning feature in this child’s clinical findings is the high axial length for his age. While the child's ethnicity is not given in the case, an axial length of around 24mm at age 5 is beyond the 75th percentile for boys of both European and Chinese ethnicity, indicating a high risk of future myopia. You can read more about this in the clinical case study entitled Axial length measurement in myopia management - how often and how much change is normal?
Additional risk factors - binocular vision status?
Checking a child’s binocular vision status is import as children at risk of myopia development can exhibit binocular vision (BV) disorders such as increased lag of accommodation and high AC/A ratio.3,4 Commenters suggested treating any BV disorders to delay the onset of myopia. Logic may dictate that addressing BV disorders will reduce a child’s risk of developing myopia, however there is currently no direct evidence to confirm this relationship between intervention and outcome. In this case, the child appears to have a normal picture of binocular vision function.
Should we manage pre-myopes prophylactically?
Currently, research on interventions for pre-myopia are limited to one small, retrospective study of 0.025% atropine which showed positive results,5 and stronger, meta-analysis evidence on increasing outdoor time.6 Commenters on the case considered both.
1. Would low dose atropine work?
Some practitioners suggested the possibility of prescribing low dose atropine to a pre-myope to delay myopia onset, especially if there are overwhelmingly strong risk factors for myopia.
Fang et al showed 0.025% atropine could delay myopia onset and reduce myopic shift in pre-myopic school aged children, in a one year, retrospective study.5 The ATOM3 Clinical Trial, currently underway, is investigating the effectivity of low dose atropine in preventing the onset and progression in pre-myopia. It is estimated for completion of data collection in mid 2023. Read more detail on atropine and pre-myopia in our blog How to identify and manage pre-myopes.
As the evidence slowly mounts for atropine, is it worthwhile considering it as a treatment for pre-myopes right now? The risk-to-benefit may not make such an endeavour worthwhile, but some parents may be keen on this for those in the high-risk category. Such a strategy would warrant thorough discussions with the parents and patient, so they are fully informed.
2. Emphasising outdoor time and visual environment
The strongest evidence for prophylactic (preventative) treatment in pre-myopes is the link between increased outdoor time and reduced risk of incidence of myopia as confirmed by a meta-analysis.6. This meta-analysis attempted to find a dose-response effect and found that less than 13 hours a week was associated with the highest odds ratio for incident myopia. Hence, aiming for at least 2 hours a day of outdoor time, on average, will overcome this risk.
Near work has also found to be associated with myopia, with the odds of myopia increasing by 2% for every one dioptre-hour more of near work per week.7 Therefore, it is important to emphasize measures such as reducing leisure screen time to less than two hours per day in school aged children, and taking regular breaks from close work. Here are some helpful links which you can share with parents from MyKidsVision.org on this topic.
- MyKidsVision.org blog - Close work and screen time in kids
- MyKidsVision.org blog - How much time should my child spend outdoors?
- MyKidsVision.org How-To Guides - Creating a healthy visual environment for children (two shareable videos)
The best part of visual environment strategies are that they're free, have arguably no downside and only the potential of benefit for the young patient.
3. Is there value in prescribing optical correction for a pre-myope?
One commenter shared that she was currently prescribing low-plus optical corrections to pre-myopes. There were suggestions also that prescribing bifocal/center distance multifocal contact lens may be effective. The rationale behind is to avoid hyperopic defocus on the retina that might trigger myopia.
The literature does not currently suggest that these methods might be effective in delaying myopia onset. Hence, parent communication is extremely important if your clinical instincts might lead you to suggest these methods. Treating binocular vision disorders associated with myopia development - such as higher AC/A ratios and esophoria, accommodative lag and intermittent exotropia - may have a logical basis to delaying myopia onset but do not have direct research evidence. For a comparison, read this clinical case on whether to manage esophoria in a pre-myope.
This child, however, is cited to have a normally functioning binocular vision system - hence there is likely little orthoptic or myopia controlling benefit to prescribing any optical correction for him.
Take home messages:
- When a child is identified as a pre-myope, it is important to place them on close follow-up (eg six-monthly reviews)
- The most strongly evidence-based prophylactic (preventative) treatment for pre-myopes is increasing outdoor time to around two hours per day on average
- There is much anticipation for the role of low-dose atropine in delaying myopia onset, with early evidence being positive. Watch this space for future updates.
About Kimberley
Kimberley Ngu is a clinical optometrist from Perth, Australia, with experience in patient education programs, having practiced in both Australia and Singapore.
About Connie
Connie Gan is a clinical optometrist from Kedah, Malaysia, who provides comprehensive vision care for children and runs the myopia management service in her clinical practice.
References:
- Flitcroft DI, He M, Jonas JB, Jong M, Naidoo K, Ohno-Matsui K, Rahi J, Resnikoff S, Vitale S, Yannuzzi L. IMI – Defining and classifying myopia: a proposed set of standards for clinical and epidemiologic studies. Invest Ophthalmol Vis Sci. 2019:28;60(3):M20-30. (link)
- Gifford KL, Richdale K, Kang P et al. IMI - Clinical Management Guidelines Report. Invest Ophthalmol Vis Sci. 2019:28;60(3):M184-203. (link)
- Mutti DO, Mitchell GL, Hayes JR et al. (CLEERE Study Group) Accommodative Lag before and after the Onset of Myopia. Invest Ophthalmol Vis Sci. 2006;47:837-846. (link)
- Mutti DO, Jones LA, Moeschberger ML, Zadnik K. AC/A Ratio, Age, and Refractive Error in Children. Invest Ophthalmol Vis Sci 2000;41:2469-2478. (link)
- Fang, P. C., Chung, M. Y., Yu, H. J. & Wu, P. C. Prevention of myopia onset with 0.025% atropine in premyopic children . J Ocular Pharm Ther 26, 341-345, doi:10.1089/jop.2009.0135 (2010). (link)
- Xiong S, Sankaridurg P, Naduvilath T, Zang J, Zou H, Zhu J, Lv M, He X, Xu X. Time spent in outdoor activities in relation to myopia prevention and control: a meta‐analysis and systematic review. Acta Ophthalmologica. 2017 Sep;95(6):551-66. (link)
- Huang HM, Chang DS, Wu PC. The association between near work activities and myopia in children—a systematic review and meta-analysis. PloS one. 2015 Oct 20;10(10):e0140419. (link)
