September 1, 2022
Is percentage treatment effect the most accurate way to express myopia control efficacy?
Treatment effect has been expressed in multiple ways, making comparing therapies and prognosis for an individual patient difficult. To better express the efficacy of myopia control treatments, the efficacy metric Cumulative Absolute Reduction in axial Elongation (CARE) was introduced by Brennan et al.1 in their paper Efficacy in Myopia Control.
CARE was designed to enable an accurate, direct comparison of treatment efficacy. It was proposed as an alternative to percentage efficacy, which is problematic when comparing across studies because percentage efficacy is influenced by multiple factors, such as the study duration and control group characteristics. Instead of efficacy being expressed as a relative percentage of the progression measured in the control group, CARE expresses an absolute efficacy: the total reduction in axial growth of the treatment group compared to the control group. CARE is not independent of time and must be expressed with reference to the time scale.
Based on their comprehensive analysis, Brennan and co-researchers have reached the following important interpretations:
- Axial length is the preferred metric for monitoring the progression of myopia.
- The initial rate of reduction of axial elongation by myopia control treatments is not sustained.
- Efficacy of myopia control treatments should be expressed as absolute, not percentage, effect.
- Cumulative Absolute Reduction in axial Elongation (CARE) emerges as a preferred efficacy metric.
- CARE is not time-independent and should be expressed with reference to the time scale.
- Maximum CARE that has been measured for existing myopia control treatments is 0.44 mm over seven years of treatment.
The most important advantage of the CARE metric is that it provides an empirically determined, evidence-based effect size that clinicians, myopia control candidates, and parents can reasonably expect for a given treatment over a given time. For more detailed information on this critical metric, I urge you to read the article Efficacy in Myopia Control and watch Why Axial Length & ‘CARE.’
Best professional regards,
Dwight H. Akerman, OD, MBA, FAAO, FBCLA, FIACLE
Chief Medical Editor
1 Brennan, N. A., Toubouti, Y. M., Cheng, X., & Bullimore, M. A. (2021). Efficacy in myopia control. Progress in Retinal and Eye Research, 83, 100923.