Incidence of myopia and 10-year change in refractive error and axial length: The Shahroud Eye Cohort Study

To describe the 10-year incidence of myopia and change in ocular biometry in older adults and their association with risk factors for myopia.

The Shahroud Eye Cohort Study is a prospective single-centre cohort study conducted in Iran. Baseline and follow-up eye assessments were conducted in 2009 and 2019. A total of 5190 participants aged 40-64 years attended the baseline assessment. Refractive data from both visits were available in 6239 eyes. The main outcomes were incidence of myopia, change in spherical equivalent refraction (SER) and axial length (AL).

Mean SER shifted from -0.35 ± 1.44 D at baseline to 0.08 D ± 1.67 D at follow-up (SER change: 0.43 ± 0.69 D). Males had more negative baseline SER than females (-0.41 D vs. -0.31 D, p = 0.009) and were more myopic at follow-up (-0.07 D vs. 0.18 D, p < 0.001). The 10-year myopia incidence was 4.60% (95% CI, 3.91-5.40). In myopic eyes, changes in SER were 0.27 D, and in AL 0.04 mm. Predictors of a myopic shift (≤-0.5 D) were longer baseline AL (odds ratio [OR], 1.30; 95% CI, 1.04-1.62), male sex (OR, 1.66; 95% CI, 1.14-2.42), older age (55-59 years: OR 2.26; 95% CI 1.31-3.89; 60-64 years: OR 3.56; 95% CI 1.79-7.08, vs. 40-44 years), low economic status (OR 1.62; 95% CI 1.05-2.50) and baseline SER (OR: 0.15; 95% CI 0.09-0.24).

In this community-based sample, the predominant refractive trend over 10 years was a hyperopic shift, while the incidence and progression of myopia were low.