Operational Definitions of Myopia Severity
Low myopia is defined as -0.50 to greater than -3.00 diopters (D), moderate myopia as -3.00 to greater than -6.00 D, and high myopia as -6.00 D or more myopic. 1
Standardized Classification System
The evidence consistently supports a three-tier classification system based on spherical equivalent refractive error:
- Low myopia: -0.50 D to > -3.00 D 2, 1
- Moderate myopia: -3.00 D to > -6.00 D 1
- High myopia: ≤ -6.00 D 3, 4, 1
Clinical Significance of These Definitions
The operational definitions are not arbitrary but reflect meaningful differences in complication risk and disease burden:
High myopia (≤-6.00 D) represents approximately one-fifth of the myopic population and carries dramatically elevated risks for vision-threatening complications 4. The odds ratios for complications increase exponentially at this threshold, with myopic macular degeneration risk increasing to OR 845.08 compared to OR 13.57 for low myopia 1.
Moderate myopia (-3.00 to > -6.00 D) shows intermediate risk elevation, with substantially higher odds of retinal detachment (OR 8.74) compared to low myopia (OR 3.15) 1.
Low myopia (-0.50 to > -3.00 D), while often considered "mild," still carries clinically significant increased risks for all major myopic complications including macular degeneration, retinal detachment, cataract, and glaucoma 1.
Important Clinical Caveats
Some literature uses -5.00 D as the threshold for high myopia in epidemiological studies 2, but the -6.00 D cutoff is more widely accepted in clinical practice and myopia control research 3, 4, 1.
The global prevalence of high myopia is estimated at 4.0% currently, projected to reach 9.8% by 2050, making these definitions increasingly relevant for public health planning 2.
Approximately 10-20% of high school children in Asia already have high myopia, with many still progressing, emphasizing the importance of early identification using these thresholds 3.