title: A quantitative geometric mechanics lens model: insights into the mechanisms of accommodation and presbyopia.
abstract: This study expands on a geometric model of ocular accommodation (Reilly and Ravi, Vision Res. 50:330-336; 2010) by relaxing assumptions regarding lens symmetry about the equator. A method for predicting stretching force was derived. Two models were then developed: Model 1 held the equatorial geometry constant at all stages of accommodation, while Model 2 allowed localized deformation at the equator. Both models were compared to recent data for axial thickness, anterior and posterior radii of curvature, surface area, cross-sectional area, volume, and stretching force for the 29-year-old lens. Age-related changes in accommodation were also simulated. Model 1 gave predictions which agreed with the Helmholtz theory of accommodation, while Model 2's predictions agreed with the Schachar mechanism of accommodation. Trends predicted by Model 1 agreed with all available experimental data, while Model 2 disagreed with recent surface area measurements. Further analysis indicated that Model 1 was fundamentally more efficient in that it required less force per diopter change in optical power than Model 2. Model 1 more accurately predicted age-related changes in accommodation amplitude. This implies that the zero-force (fully accommodated) state geometry changes with age due to a shifting balance in residual stresses between the lens and capsule.
authors.affiliation: Biomedical Engineering, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, United States. Electronic address: matthew.reilly@utsa.edu.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Reilly
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D000375:Aging / Q000502:physiology*; D004548:Elasticity; D006801:Humans; D007908:Lens, Crystalline / Q000033:anatomy & histology / Q000502:physiology*; D008962:Models, Theoretical; D011305:Presbyopia / Q000503:physiopathology*
keywords: Accommodation; Lens; Lens curvature; Lens stretching; Optomechanics; Presbyopia