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H.A. Weeber, M. Dubbelman, G.L. van der Heijde; Verification of a Mechanical Model of Accommodation Versus Real Patient Data . Invest. Ophthalmol. Vis. Sci. 2003;44(13):235.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To verify a mechanical model of accommodation versus real patient data. Methods: The shapes and positions of the refracting surfaces in the left eye of one 25-year-old subject were measured at nine different accommodative states, using corrected Scheimpflug photography. At each accommodative state, the surface radii, asphericity and central thickness of the lens and cornea were measured as well as the position of the lens relative to the cornea. The measurements were taken with a dilated pupil. The results were analyzed using the patient's maximum pupil diameter and also a pupil diameter of 3-mm. The measurements were compared with results derived from a Finite Elements simulation of the mechanical aspects of accommodation. The computer model used the measured lens geometry at maximum accommodation as input geometry. Subsequently, this lens was stretched through the zonular fibers, simulating disaccommodation. The maximum stretch of the lens was set to a value according to MRI measurements in the literature corresponding to a 25-year-old subject. The surface shapes were fit with aspheres, to the same pupil diameters as the measured data. Using an equivalent refractive index, calculated from the shape of the refracting surfaces, axial length measurement and refraction, all results were converted into diopters of accommodation and compared with the Scheimpflug data. Results: The maximum accommodation measured was 6.8 diopters. Maximum visible aperture diameters were 7.7 and 6.2 mm for the anterior and posterior lens surface respectively. As expected, the lens radii decreased with accommodation. The asphericity of the anterior lens surface increased with increasing accommodation, while the asphericity of the posterior surface remained unchanged. The calculations using a 3-mm aperture show an accommodation, which corresponds very well with the measurements, resulting in a correlation coefficient of 0.9. For a large aperture the correlation coefficient is 0.8. The results for the large aperture show that the calculations do not follow the measured changes in asphericity. Conclusions: The mechanical model used is able to predict the amount of accommodation measured in a real patient. However, it does not predict the lens asphericity and asphericity changes measured during accommodation.
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