Differentiation Between Moderate Versus High Myopia: The 2-Continent Eye Study

To determine the cutoff value in axial length between moderate myopia versus high myopia in dependence on the prevalence of myopic macular degeneration (MMD).

Population-based studies conducted in Russia, China, and India.

The project included the population-based investigations of the Beijing Eye Study (n = 3325; age: 40+ years), Russian Ural Eye and Medical Study (n = 5586 participants; age: 40+ years), Ural Very Old Study (n = 541; age: 85+ years) and Ural Children Eye Study (n = 4255; age: 6+ years), and Central India Eye and Medical Study (n = 4467; age: 30+ years).

The participants underwent a series of general medical and ophthalmic examinations, including fundus photography and ocular biometry. Myopic macular degeneration was defined according to the Meta-analysis for Pathologic Myopia Study Group.

Prevalence of MMD in dependence on axial length.

The total study population included 36 123 eyes (18 471 individuals) (age: 47.4 ± 23.4 years; range: 6-100 years) (axial length: 23.2 ± 1.1 mm; range: 18.22-34.20 mm). In the total study population, higher MMD stage was associated with longer axial length (β: 0.55; B: 0.14; 95% confidence interval [CI]: 0.14-0.15; P < 0.001), older age (β: 0.09; B: 0.001; 95% CI: 0.001-0.001; P < 0.001), female sex (β: 0.12; B: 0.07; 95% CI: 0.06-0.07; P < 0.001), and Indian ethnicity (β: 0.10; B: 0.07; 95% CI: 0.06-0.07; P < 0.001). Higher prevalence of MMD stage 2+ and 3+ correlated with longer axial length (odds ratio [OR]: 9.10; 95% CI: 6.93-11.9; P < 0.001 and OR: 6.90; 95% CI: 5.14-9.26; P < 0.001, respectively), older age (OR: 1.06; 95% CI: 1.04-1.08; P < 0.001 and OR: 1.08; 95% CI: 1.05-1.11; P < 0.001, respectively), and Indian ethnicity (OR: 6.96; 95% CI: 2.70-17.9; P < 0.001 and OR: 3.69; 95% CI: 1.26-10.8; P = 0.02, respectively). The turning points of the regression curves of the associations of axial length with prevalence of MMD stage 2+ and 3+ were located at axial length values of between 26.0 and 26.5 mm, respectively.

The axial length-related cutoff for moderate versus high myopia was located approximately at 26.0 and 26.5 mm for the prevalence of MMD stage 2+ and 3+, respectively, with higher values for younger individuals. Myopic macular degeneration prevalence was higher in the Indian cohort.

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