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N. Ravi, M. A. Reilly; An Improved Geometric Model of Accommodation. Invest. Ophthalmol. Vis. Sci. 2010;51(13):791.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the utility of a geometric model of accommodation in quantitatively predicting both optical and mechanical features of accommodation.
The published geometric lens model (Reilly and Ravi, ARVO E-Abstract 6137, 2009; Vision Res. in press) was improved by utilizing data from Hermans et al. (IOVS 50:281-289, 2009) to allow an equatorially asymmetric formulation. Input data from Dubbelman et al. (Vision Res. 45:117-132, 2005) and Strenk et al. (IOVS 45:539-545, 2004) were used to define the geometry of the 29-year-old lens in the fully accommodated state. Optical and mechanical responses, including stretching force, were quantitatively predicted by the model. Model predictions were objectively compared with recent data.
The model gave quantitative agreement with the radii of curvature and thickness results of Dubbelman et al. (2005) (Fig. 1). Relative error in L2 norms relative to the best available data were 3.4%, 1.8%, 3.4%, 2.1%, 29.2%, 8.7%, 12.5%, and 15.1% for anterior radius of curvature, posterior radius of curvature, axial thickness, optical power, stretching force, cross-sectional area, surface area, and volume, respectively.
This simple model does not require any knowledge of the mechanical properties of the lens, yet qualitatively predicts the optomechanical performance of the young human lens to a high degree of accuracy. Linear elastic properties of the capsule were used to estimate the force. The predicted stretching force is somewhat lower than that measured by Manns et al. (IOVS 48:3260-3268, 2007). This disparity is likely due to a lack of consideration the strain energy imparted on the lens fiber cells by the capsule and the experimental methods employed. Still, it does indicate that the majority of the force required to stretch the lens is due to area dilation of the capsule.Figure 1: Comparison of model predictions with recent data for various optomechanical measurements including axial thickness, radii of curvature, optical power, and stretching force.
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