Hyperopic eyes are structurally more dynamic than myopic eyes during accommodation: an in-vivo investigation

Purpose: The impact of different refractive errors on accommodative structural changes remains unclear. Novel swept-source imaging technology in anterior segment optical coherence tomography (AS-OCT) has enabled in vivo investigation of the accommodating eye. This study investigated ocular structural change and corresponding functional responses during accommodation in individuals with emmetropia, myopia, and hyperopia.
Methods: Adults (n = 46; mean age, 22.15 ± 3.00 years) with normal accommodation and a wide range of refractive errors (spherical equivalent refraction [SER]: −7.50 D to +7.88 D) were recruited. CASIA2 AS-OCT measured anterior segment changes during accommodation stimulated by the use of inbuilt accommodative targets and bespoke external stimuli at five different accommodative demands (0 D, 2 D, 3 D, 4 D, and 6 D) and under cycloplegia. Simultaneously, changes in refractive state were measured using the PowerRefractor3 photorefraction system.
Results: Lens thickness (LT), anterior chamber depth (ACD), lens diameter (LD), anterior segment length (ASL), anterior lens radius of curvature (ALRC), and posterior lens radius of curvature (PLRC) changed significantly during accommodation (all P < 0.001). Accommodative changes in LT, ACD, and ASL were significantly associated with the level of SER (all P < 0.05), as more hyperopic eyes showed significantly greater per-diopter change than myopic eyes in LT (P = 0.014) and ACD (P = 0.039) for comparatively similar accommodative response (P > 0.9). The analysis of lens position showed that cycloplegia induced posterior displacement of the lens. The CASIA2 internal accommodative target and the external proximal target induced similar structural and functional accommodative responses.
Conclusions: There are significant differences between structural changes seen in accommodating eyes with different types and magnitudes of refractive error, with hyperopic eyes showing greater changes in LT and ACD than myopic eyes during accommodation.