We have a convincing evidence base for several optical, one pharmacological and visual environment solutions to reduce the progression of childhood myopia, but nothing guarantees 100% efficacy. Because of this, even in when under a successful myopia management strategy, a child’s myopia may still progress. It is important to manage parental and patient expectations about myopia management – that we cannot promise to stop progression but we can slow it down. The paediatric eye is expected to grow until age 12-13 through the process of emmetropization, hence some axial elongation over this period can be attributed to normal growth and not myopia progression. Don Mutti and colleagues analysed refractive and biometric data in the CLEERE (Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error) study and described that, on average, the paediatric eye will elongate by around 0.1mm per year before additional elongation contributes to myopia progression.1 It’s a little more than that for younger kids, and a little less than that for older kids.
Once accelerated growth has been triggered through myopia development, progression occurs as a faster rate for younger children – around -1.00D per year for a Caucasian 7 year old and -1.25D for an Asian 7 year old – than for older children, who reduce to around -0.50 progression per year, on average, if corrected with single vision distance (SVD) spectacles.2 The Brien Holden Vision Institute has recently released a myopia calculator whereby inputting the age and current refraction will output the predicted level of myopia by age 18. The user can then apply different treatments which demonstrate the reduction in end-point myopia by their individual efficacy. The calculator can be freely downloaded.
Predict or retrospect?
These predictions rely on averages, which is the best evidence based method with the current data available. There is potential for complication, though, in predicting a future-forward level of myopia when significant individual variation occurs. The aforementioned CLEERE study, which followed more than 2000 children over a decade, showed that the younger you become myopic the faster you will progress, and the more myopic you will become. However, their data also showed that for children who became myopic (<-0.50) at age 6, some may only progress to -1.00 while others progress to -6.00.3 This pattern is also evident across older age groups – later onset generally leads to lower final level of myopia, but myopia progression can be unpredictable, so an alternative approach is to compare progression after it has occurred to expected rates in ‘untreated’ children, where this refers to single SVD correction.2
If an 8-year-old Caucasian child has progressed -0.50 across one year of myopia management, their parents may be disappointed in the outcome, where in fact this represents a 50% myopia control effect compared to their average SVD spectacle wearing counterpart. This much progression in an 11 year old, however, indicates inadequate myopia management. The image below provides a useful reference for the expected progression per year by age for Caucasian and Asian children (in red),2 if they were wearing a single vision correction. This data has been calculated from meta-analysis of the control groups from 20 myopia control studies. The figures in yellow show the amount of progression per year which would indicate 33% myopia control efficacy (as achieved by progressive/bifocal 4, 5 or novel spectacle lens designs6 in certain conditions), and the green figures indicate 50% efficacy (typically achieved by multifocal soft contact lenses, OrthoK and low dose atropine).7-10
If a child's myopia doesn't progress over your year of treatment - happy days! Perhaps you've achieved the magical 100% efficacy for that child, or perhaps the unpredictable, natural course of their myopia was slowing anyway. If their myopia does progress, though, you can use this image as a reference tool to discuss how the progression compares with the average for an 'untreated' (single vision corrected) child of the same age, and adjust your management plan accordingly.
Putting both tools together - you may find the BHVI calculator most useful for initial discussions of the 'why' of myopia management, to help parents and patients understand the imperative. Subsequently, the table above (distilled from a study authored by the BHVI!) may be more useful to compare a child's progression to 'untreated' (red figures) and 'goal' (50% efficacy green figures) along the treatment path.