Longitudinal Changes in Layered Retinal Thickness during Axial Elongation in Healthy Myopic Eyes

Purpose: To investigate longitudinal changes in foveal retinal sublayer thicknesses during axial elongation. Methods: From February 2013 to September 2014, a prospective cohort was established comprising pediatric patients aged < 13 years exhibiting myopia with a spherical equivalent of less than -0.75 diopters (D). At each visit, the foveal retinal thickness was measured using spectral-domain optical coherence tomography and sublayers were distinguished as follows: 1) total retinal layer, 2) inner retinal layer, 3) retinal nerve fiber layer, and 4) ganglion cell-inner plexiform layer. The average thickness was calculated based on the nine subfields of the Early Treatment Diabetic Retinopathy Study (ETDRS) map and compared between the initial and final visits. Intra-individual correlations were analyzed using a linear mixed-effects model. Results: Twenty-three subjects (46 eyes) were observed for 2.7 ± 1.0 years. During that period, the myopia progressed (spherical equivalent of cycloplegic refraction: from -4.26 ± 2.34 to -6.09 ± 2.64 D; p < 0.001, paired t-test), and the axial length increased from 24.80 ± 1.28 to 25.58 ± 1.38 mm (p < 0.001, paired t-test). Nevertheless, the thicknesses of foveal retinal layers (total retinal layer, inner retinal layer, retinal nerve fiber layer, ganglion cell-inner plexiform layer) showed no significant change in any of the nine ETDRS subfields (all p > 0.05, linear mixed-effects model). Conclusions: The foveal retinal sublayers maintained their thicknesses despite axial elongation, indicating that the foveal retinal structure, which is critical to visual acuity, is preserved even in elongated, myopic eyes.