Evidence-based medicine can help clinicians with myopia treatment decisions
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For eye care providers who practice evidence-based medicine, one guiding principle is the reliability of a treatment’s effectiveness, which goes far beyond intuition, experience and training and instead depends on sound, valid science.
The goal of evidence-based medicine is to provide the highest quality care cultivated from the best clinical evidence available, with the aim to improve a patient’s quality of life. It must be better for the individual than the untreated, natural course of the disease.
However, treatments are rarely 100% effective, making it necessary for clinicians to assess intervention efficacy, weigh benefits against risks and make decisions that prioritize patient well-being.
NNT offers a risk-to-benefit snapshot
One metric that can help doctors make informed treatment decisions is a statistical calculation known as Number Needed to Treat (NNT), which is often used in randomized controlled trials and health assessments.
NNT provides an estimate on the number of patients that need to be treated for one patient to achieve a benefit and, in turn, prevent one additional adverse outcome. To calculate NNT, the absolute risk reduction (ARR) of a treatment needs to be determined first. The AAR is the difference in the event rates between a study’s treatment group and the control group.
The NNT is the inverse of the ARR and can be calculated by taking 100 and dividing it by the ARR. For example, if a hypothetical stroke medicine is clinically found to reduce deaths by 50% — the ARR in this case — this drug would have an NNT of 2 (100 ÷ 50 = 2).
Studies have reported that a lower NNT indicates a better chance of a health benefit (Chong C, et al.). If a treatment has an NNT value of 1, this indicates that each person who receives it would benefit. However, if a treatment has an NNT of 100, this suggests that 100 patients would need to be treated for just one individual to reach the specified end point and achieve a positive outcome.
Of course, NNT should not be the sole factor in treatment decisions; doctors must weigh research findings against factors like quality of life, cost and potential side effects through a comprehensive risk-benefit discussion with patients. Doctors should also recognize when scientific study results are misinterpreted in published reports, as misleading data can influence decisions.
NNT, treatment response rates in myopia management
One study by Cho and colleagues examined the risk for rapid progression and NNT in younger and older children using combined data from two previous orthokeratology investigations, ROMIO and TO-SEE. The younger participants, aged 6 to 8 years, in the control group had the greatest and most rapid axial elongation at the end of 24 months. Additionally, ortho-K lens wear in these participants significantly reduced the risk for rapid progression by 88.8%. The 2-year NNT for the younger ortho-k subgroup was approximately 2, while the 2-year NNT for the older ortho-K subgroup, aged 9 to 12 years, was roughly 12.
The LAMP2 study evaluated the efficacy of low-dose atropine eyedrops at 0.05% and 0.01% concentrations for delaying the onset of myopia (Yam JC, et al.). The 2-year cumulative incidence of myopia was 28.4% and 45.9%, respectively, and 53% for placebo. Percentages of participants with fast myopic shift at 2 years were 25%, 45.1% and 53.9%. Even at the stronger 0.05% concentration, one could consider 28.4% and 25% as nonresponse rates due to formulation, efficacy, compliance or more.
NNT’s role in myopia control
When factoring NNT into myopia treatment, a recent investigation by Bullimore and colleagues found the potential benefits of myopia control far outweighed the risks.
The study assigned myopia control a low NNT value — approximately 4.1 to 6.8 — to prevent 5 years of visual impairment. The findings indicated that less than one in 38 individuals would experience a loss of vision as a result of myopia control.
Additionally, the investigation underscored the need to not only treat myopia, but to treat it early, since each additional 1 D of myopia was tied to an increased risk for sight-threatening eye diseases. Specifically, every 1 D of myopia was associated with a 67% increased risk for myopic maculopathy, a 20% increased risk for open-angle glaucoma, a 21% increased risk for posterior subcapsular cataract and a 30% increased risk for retinal detachment.
Clinical trials demonstrate strong treatment outcomes
Now that myopia management has become a standard of care in the profession, eye care providers need to consider the data when making informed treatment decisions for their patients.
In the longest-running soft contact lens study among children, MiSight 1 day lenses (CooperVision) demonstrated a 90% response rate, providing maximum benefit to younger, faster-progressing children (Chamberlain P, et al.). This response corresponds to an NNT of 1.1 for MiSight 1 day in age-appropriate children.
Myopia cases are rising globally, but strong scientific evidence from myopia control studies that clearly indicate how patients benefit from treatment should assure providers to prescribe with confidence with the end goal of preserving a child’s vision and long-term ocular health.
References:
- Bradley EA, et al. Arch Ophthalmol. 2006;doi:10.1001/archopht.124.1.121.
- Bullimore MA, et al. Ophthalmology. 2021;doi:10.1016/j.ophtha.2021.04.032.
- Chamberlain P, et al. Optom Vis Sci. 2022;doi:10.1097/OPX.0000000000001873.
- Chong C, et al. J Clin Epidemiol. 2006;doi:10.1016/j.jclinepi.2005.08.005.
- Cho P, et al. Invest Ophthalmol Vis Sci. 2017;doi:10.1167/iovs.16-20594.
- Perneger TV, et al. J Gen Intern Med. 2011;doi:10.1007/s11606-011-1810-x.
- Resolution: The standard of care for myopia management by optometrists. https://worldcouncilofoptometry.info/resolution-the-standard-of-care-for-myopia-management-by-optometrists/.
- Varner P. Optom Vis Sci. 2006;doi:10.1097/01.opx.0000249979.36298.40.
- Yam JC, et al. JAMA. 2023;doi:10.1001/jama.2022.24162.
For more information:
Kyle D. Klute, OD, practices at Good Life Eyecare, with offices in Omaha, Nebraska, and Glenwood, Iowa.
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