Weighing up the risks and benefits of myopia control

[Link to open access paper]

Paper title: The risks and benefits of myopia control

Authors: Bullimore, Mark A (1); Ritchey, Eric R (2); Shah, Sunil (3); Leveziel, Nicolas (4); Bourne, Rupert R A (5); Flitcroft, D Ian (6)

1. College of Optometry, University of Houston, Houston, Texas.
2. College of Optometry, University of Houston, Houston, Texas.
3. Birmingham and Midland Eye Centre, Birmingham, United Kingdom; Ophthalmic and Vision Sciences Research Group, Life and Health Sciences, Aston University, Birmingham, United Kingdom.
4. Service d'ophtalmologie, Centre Hospitalier Universitaire (CHU) Poitiers, Poitiers, France; University of Poitiers, Poitiers, France; Centre d'Investigation Clinique (CIC 1402), Poitiers, France; Institut National de la Santé et de la Recherche Médicale (INSERM 1084), Poitiers, France; Vision & Eye Research Institute, School of Medicine, Anglia Ruskin University, Cambridge, United Kingdom.
5. Vision & Eye Research Institute, School of Medicine, Anglia Ruskin University, Cambridge, United Kingdom; Department of Ophthalmology, Cambridge University Hospital, Cambridge, United Kingdom.
6. Department of Ophthalmology, Children's University Hospital, Dublin, Ireland; Centre for Eye Research Ireland, School of Physics, Clinical and Optometric Sciences, Technological University Dublin, Dublin, Ireland.

Date: Nov 2021

Reference: Bullimore MA, Ritchey ER, Shah S, Leveziel N, Bourne RRA, Flitcroft DI. The Risks and Benefits of Myopia Control. Ophthalmology. 2021 Nov;128(11):1561-1579.

The global rise in myopia prompts efforts to slow its progression, as it links to eye issues and future visual impairment. Yet, interventions intended to control myopia also carry risks of inducing visual impairment. Bullimore et al. explore whether a 1D reduction justifies these risks. Methods like atropine, specific lenses, and orthokeratology have shown promise in slowing myopia.^1-4  The paper summarizes the risks associated with each method, estimating the potential years of visual impairment and increased risk of sight-threatening conditions based on myopia levels. The study models the risk of visual impairment in relation to myopia severity, projecting years of impairment and potential prevention through myopia control.

The known risks of commonly used myopia control therapies were reviewed:

• Spectacle lenses: Some designs may reduce peripheral vision due to positive dioptric power changes towards the lens edges.
• Atropine: Side-effects include photophobia and near vision issues due to pupil dilation and accommodation loss; these can be countered with photochromic and/or multifocal lenses. Systemic absorption extent is unclear, with no adverse reports to date.
• Soft contact lenses: Non sight-threatening corneal events estimated at 300-400 per 10,000 patient-years for adults and 97 per 10,000 patient-years for children aged 8-12 years. Potentially sight-threatening microbial keratitis risks estimated at 20 per 10,000 adult patient-years, dropping to 2-4 with daily disposable lenses. For children aged 8 to 12 years, this was 0 per 10,000 patient-years.
• Years of visual impairment calculations for contact lenses: To result in 1 year of vision loss, 7.5 patients have to wear high-risk lenses for 5 years. For 5 years of vision loss, 945 patients have to wear (daily wear) low-risk lenses for 5 years.
• Overnight orthokeratology: Risk of microbial keratitis in children thought to be similar to that of adults wearing extended wear soft lenses at 14 per 10,000 patient years.⁵ 

Increasing levels of myopia are associated developing several ocular pathologies. Every additional 1D of myopia gave an increased risk of 58%, 20%, 21%, and 30% for myopic maculopathy, open-angle glaucoma, posterior subcapsular cataract and retinal detachment, respectively. Reducing myopia progression by 1D would be expected to reduce the likelihood of developing myopic maculopathy by 37%.

Predicted mean years of visual impairment ranged from 4.42 for -3D myopes to 9.56 for -8D. A reduction of 1D in myopia would lower these by 0.74 and 1.21 years, respectively. The number of patients needed to treat (with myopia control) to prevent 5 years of visual impairment is between 4.1 and 6.8. In comparison, less than 1 in 38 patients will experience vision loss as a result of myopia control treatment.

The risk of vision loss with spectacle lenses and atropine is considered negligible. It is assumed that most risk associated with myopia control is associated with contact lenses.

• The data has shown that daily soft lens wear in children is at least as safe as in adults, with daily disposable lenses potentially further mitigating the risk.⁶
• The infection risk for 8-12yr olds is low. This is important to recognise as this is the age myopia control is most likely to be commenced.
• The risk of microbial keratitis in overnight orthokeratology wear in children is similar to other overnight methods (extended wear of soft contact lenses) in adults.  

Therefore, while contact lenses are associated with the greatest risk of all myopia treatment options, the risk is relatively low for children.

 The benefits of myopia control far outweigh the risks of the 5 years of contact lens wear required to achieve 1D of control

• 1D of myopia control can prevent between 0.74 and 1.22 (9-15 months) of visual impairment for myopia levels between -3 and -8D.
• The years of visual impairment that may be associated with 5 years of contact lens wear (based on published range of incidence of microbial keratitis) is between 53 and 1312 years of visual impairment per 10, 000 patients. This corresponds to 0.0053 to 0.1312 years per patient.
• The number needed to harm (NNH) for 5 years of visual impairment is between 38 and 945. That is, even for the highest incidence of MK (25/10,000), 38 patients would need to be exposed to induce 5 years of visual impairment. In comparison, only 4.11 to 6.75 patients would need to have their myopia reduced by 1D to prevent 5 years of visual impairment.
• For the level of risk that may be expected for myopia control using daily disposable contact lenses (1/10,000) the NNH outweighs the NNT by a ratio of 140 for a person of -3D of myopia and 230 for a person with -8D of myopia.

For lower risk therapies, the benefits are compelling, but for smaller amounts of myopia control or higher levels of risk, the benefits are still valid.

 The benefit of slowing myopia progression by 1D cannot be underestimated.

• The authors calculated the benefit of slowing myopia progression by 1D of myopia as the difference in years of visual impairment.
• Controlling myopia such that a patient destined to be a -3D instead ends up as a -2D myope should prevent an average of 0.74 years of visual impairment. Likewise, controlling a -8D myope to a -7D myope would prevent 1.22 years of visual impairment
• The justification for utilising myopia control interventions is to limit myopia progression in order to reduce the risk of visual impairment later in life, where the condition of myopia is in itself a risk factor for visual impairment.

When assessing the risk to benefit of myopia control treatments, a number of elements should be considered: the efficacy of the intervention and any treatment specific risks, the level of myopia and the risk of the likely impaired vision from the myopia severity.

A summary of the long-term benefits of myopia control by Bullimore and Brennan⁷ included reduced risk of ocular pathologies, reduced dependence on a refractive correction, better corrected and uncorrected visual acuity, improved vision-related quality of life and minimal residual refractive error if corrective refractive surgery is sought.  

The model used in this study to assess risk and benefit had some assumptions impacting accuracy:

1. Direct comparisons were made between myopia control treatment and myopic pathology-related visual impairment, but differences exist:

   • Myopia treatment complications arise from interventions, while myopia pathologies result from natural progression.
   • Myopia control impact occurs earlier and has a longer-lasting effect into adolescence, contrasting with ocular pathologies affecting later years.
   • Visual impairment from myopia is likely binocular, while contact lens complications are typically monocular.

2. Assumptions included a fixed treatment effect and universal 1D treatment feasibility, ignoring efficacy reduction over time. An adjusted model could explore treatment variations.

3. Age-related interpolation was used due to limited data (up to 75yrs), potentially overlooking age-related myopia differences in older populations.

Other considerations and areas for further research:

• Inclusion of data for non-white European populations.
• Lack of data on myopia control benefits, requiring assumptions about rebound effects.
• Establishing a causal link between refractive error, ocular disease, and the impact of reducing myopia on risks, considering the time delay between myopia control and increased risk.
• Challenges with interpreting results using need-to-treat (NNT) and needed-to-harm (NNH) values without specified follow-up or treatment periods.
• Full cost-to-benefit analysis for myopia control, including adverse ocular events and reductions in ocular morbidity. 

Title: The Risks and Benefits of Myopia Control

Authors: Mark A Bullimore, Eric R Ritchey, Sunil Shah, Nicolas Leveziel, Rupert R A Bourne, D Ian Flitcroft

Purpose: The prevalence of myopia is increasing around the world, stimulating interest in methods to slow its progression. The primary justification for slowing myopia progression is to reduce the risk of vision loss through sight-threatening ocular pathologic features in later life. The article analyzes whether the potential benefits of slowing myopia progression by 1 diopter (D) justify the potential risks associated with treatments.

Methods: First, the known risks associated with various methods of myopia control are summarized, with emphasis on contact lens wear. Based on available data, the risk of visual impairment and predicted years of visual impairment are estimated for a range of incidence levels. Next, the increased risk of potentially sight-threatening conditions associated with different levels of myopia are reviewed. Finally, a model of the risk of visual impairment as a function of myopia level is developed, and the years of visual impairment associated with various levels of myopia and the years of visual impairment that could be prevented with achievable levels of myopia control are estimated.

Results: Assuming an incidence of microbial keratitis between 1 and 25 per 10 000 patient-years and that 15% of cases result in vision loss leads to the conclusion that between 38 and 945 patients need to be exposed to 5 years of wear to produce 5 years of vision loss. Each additional 1 D of myopia is associated with a 58%, 20%, 21%, and 30% increase in the risk of myopic maculopathy, open-angle glaucoma, posterior subcapsular cataract, and retinal detachment, respectively. The predicted mean years of visual impairment ranges from 4.42 in a person with myopia of -3 D to 9.56 in a person with myopia of -8 D, and a 1-D reduction would lower these by 0.74 and 1.21 years, respectively.

Conclusions: The potential benefits of myopia control outweigh the risks: the number needed to treat to prevent 5 years of visual impairment is between 4.1 and 6.8, whereas fewer than 1 in 38 will experience a loss of vision as a result of myopia control.

[Link to open access paper]