The ‘hyperopic reserve’ and treatment in pre-myopia - Q&A with Dr Peter Chen

Human eyes are shorter at birth and therefore hyperopia is the predominant refractive error from birth. As we grow the eye becomes longer and refraction changes towards emmetropia. If the eye growth overshoots then myopia will develop. We call the hyperopic refractive state immediately before myopia onset the “hyperopic reserve”. We know that children who have a lower amount of hyperopic reserve are at greater risk of developing myopia in the future. 

In a 2023 study of which I was lead author, we investigated longitudinal data to look at the relationship between hyperopic reserve and future risk of myopia. The data spanned visits for over 870,000 patients from 2005 to 2021 and children aged 4 to 18 years. Concerningly, we found that the mean age of myopia onset reduced by three years over that time, from 10.6 years in 2005 to 7.6 years in 2021.

When it came to understanding hyperopic reserve, we found a dose-response relationship, where the risk of myopia increased rapidly when the spherical equivalent refractive error (SERE) was less than +1.50D. With SERE’s less than +1.50D, the risk (hazard ratio) of myopia increased by 0.325 for each 0.10D reduction in hyperopic reserve. This ‘safety threshold’ of hyperopic reserve was +1.50D, regardless of age and gender.¹

The faster axial length growth and myopia development observed in Chinese children likely stem from ethnic variations in eye growth trajectories and increased academic pressures. Unlike the CLEERE study's ethnically diverse cohort, where only 13.7% were Asian,² our study focuses on Chinese children, who tend to have higher baseline risks for myopia. Additionally, our data was sourced from a single tertiary hospital, which may overrepresent myopic children, since hyperopic or “pre-myopic” children are less likely to attend as they are visually normal. All of these could explain why our results were different to the CLEERE study.

In the CLEERE study, it was also found that the hyperopic threshold cutoff reduced with increasing age, whereas our model did not find a significant effect for age, and a very weak effect with gender. It remains unclear why the hyperopic cutoff did not decline with age in our analysis.

I believe hyperopic reserve is the most important factor, and I also find a history of rapid axial length growth quite compelling. Other risk factors I assess include Asian descent, younger age, and the presence of myopic parents. 

For this study we randomly allocated 108 Chinese children aged between 6-9.9, with a spherical equivalent refraction of plano to +2.00, into two groups. One group wore spectacle lenses with highly aspherical lenslets (HAL) and the other group wore single vision spectacle lenses (SVL). We then measured their cycloplegic refraction and axial length at 6 and 12 months follow-up visits.    

We found that there was a dose-response relationship between axial length elongation and HAL lens wearing time. Children who wore the HAL glasses for >30 hours per week had significantly less axial length elongation compared to SVL children over 12 months (0.11mm compared to 0.27mm, p<0.01).³ This tells us that wearing HAL lenses may delay myopia onset in pre-myopic children by reducing axial length growth, however this is only achieved with consistent full time lens wear. 

I always recommend increasing outdoor time as first-line intervention.^4,5 For those who may be willing to comply with spectacle lens wear, I would recommend optical treatment as it has minimal side effects. It is absolutely crucial to ensure the recommended wearing time schedule is achieved in this case, being at least 30 hours per week, according to the research.³ For children who do not respond well to optical treatment, low dose atropine is also worth implementing. 

My rule of thumb is doing anything is better than doing nothing in pre-myopic children. 

Managing adult complications of myopia, such as retinal tears, detachments, and myopic maculopathy, often leaves ophthalmologists with limited options. These issues largely stem from excessive axial elongation in youth, underscoring the need to target myopia early. 

If we actively manage myopia during childhood, we may achieve on average of 0.15 to 0.20 mm of cumulative absolute reduction in axial elongation (CARE) per year, when compared to single vision lens wear.⁶ Whereas if we delay myopia onset by one year, we can reduce final axial length by up to 0.5mm in adulthood.  That is, 0.50 mm of CARE per year, which is a substantial advantage over treatments aimed at controlling myopia progression after it has already developed in children.

Therefore, pre-myopia intervention offers significantly greater benefits for myopia management and mitigating its severe complications later in life.