A three-year cohort study comparing myopia progression between children with axial and refractive myopia

Objective   To compare the changes in spherical equivalent (SE) and axial length (AL) between children with axial myopia and refractive myopia.

Methods  A prospective cohort study was conducted.A total of 1 738 students from grades 1 to 6 were recruited from two consistent 9-year schools in the Binhai New Area of Tianjin using cluster random sampling.Visual acuity, refractive status, and ocular biological parameters were measured from February to May in 2018 and 2021.Participants were categorized into subgroups as follows: low, moderate, and high myopia based on SE; longer AL group and shorter AL groups based on AL; and steeper cornea and flatter cornea groups based on corneal curvature radius (CCR). Myopic children were further classified into the following groups: axial myopia (longer AL and flatter cornea), refractive myopia (shorter AL and steeper cornea), mixed myopia (longer AL and steeper cornea), and non-axial non-refractive myopia (shorter AL and flatter cornea). Changes in SE (ΔSE) and AL (ΔAL) at the end of the follow-up period were compared among the different classification groups.This study adhered to the Declaration of Helsinki and was approved by the Ethics Committee of Tianjin Medical University Eye Hospital (No.2020KY-39). Written informed consent was obtained from the guardians of all participants.

Results  The ΔSE in the longer AL group was (-1.57±1.52)D, which was significantly greater than (-1.17±1.47)D in the shorter AL group ( t=3.99, P<0.01). The ΔAL in the steeper cornea group was (0.92±0.50)mm, which was significantly greater than (0.86±0.54)mm in the flatter cornea group ( t=-2.12, P=0.04). Among children aged 10-12 years, males, and the low myopia, SE progression was faster in those with longer AL compared to shorter AL, with statistically significant differences ( t=2.66, 3.31, 3.90; all P<0.05). In children aged 10-12 years, AL growth was faster in the longer AL group than in the shorter AL group, with a statistically significant difference ( t=-1.29, P=0.04). Among females and the low myopia, AL growth was faster in those with steeper corneas than in those with flatter corneas, with statistically significant differences ( t=-3.22, -2.43; both P<0.05). Refractive myopia had a smaller ΔSE than axial myopia and the difference was statistically significant ( P<0.05). Within the low myopia, SE progression was greater in axial myopia than in refractive myopia, with a statistically significant difference ( P<0.05).

Conclusions  Among myopic children, those with longer axial lengths exhibit faster SE progression, while those with steeper corneas show faster axial elongation.Among children with low myopia, axial myopia is associated with a greater risk of SE progression than refractive myopia.