Layer-specific quantitative analysis of accommodation in the human lens using long-range OCT and machine learning

BACKGROUND: The crystalline lens undergoes complex deformations during accommodation. However, in vivo characterization of the accommodation-induced dynamics of the internal lens structures has been hindered by limited imaging depth and by the difficulty of segmenting these subtle features. In this study, long-range optical coherence tomography (OCT) was used to visualize and measure the morphology of the accommodating eye, including the cornea, entire lens, nucleus, and optical signal discontinuity (OSD) zones (C1-C4) in the lens cortex. METHODS: Sixty healthy young adults (mean age 26 ± 7 years) were imaged with a commercial long-range OCT system at four accommodative demands (0, 2, 4, and 6 D) using a modified Badal unit. Machine learning-assisted segmentation of the corneal and lens interfaces enabled correction of the OCT images for light refraction. The central densitometric depth profile was used to identify and manually delineate the anterior and posterior OSD zones in the crystalline lens cortex. The analysis of accommodation-related changes in eye geometry included intraocular distance, OSD-zone thickness, and surface curvature. RESULTS: Accommodation induced significant thickening and curvature changes in both the whole lens and its nucleus. Zonal analysis revealed localized changes within the cortex, with the inner C4 zones showing the largest accommodative thinning and contributing to lens deformation, whereas the peripheral cortical zones exhibited minimal changes. These internal lens deformations were accompanied by typical biometric responses of the eye to accommodation, including reduced anterior chamber and vitreous chamber depths across demands, and a slight increase in ocular axial length at lower accommodative demands. CONCLUSIONS: This study provides a map of lenticular deformation during accommodation, identifying the cortical C4 zones and the lens nucleus as the primary deformation compartments. In contrast, the peripheral cortex remains relatively passive. These findings demonstrate that accommodation cannot be fully described using global lens metrics alone. Therefore, biomechanical and optical models should incorporate cortical and nuclear behavior instead of treating the lens as a homogeneous structure. The quantitative data presented here extend our understanding of the OSD zones and establish a baseline for future investigations of age-related and pathological alterations in accommodation and lens structures.