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E. Hermans, P. J. W. Pouwels, M. Dubbelman, J. P. A. Kuijer, R. G. L. van der Heijde, R. M. Heethaar; Volume of the Human Lens and Surface Area of the Capsular Bag During Accommodation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3779.
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A change in surface area of the capsular bag or a change in lens volume, can indicate whether the change in shape of the lens during accommodation is due to either the compressibility or the elasticity of lens material.
3D Magnetic Resonance Imaging (MRI) was used to undistortedly image the complete shape of the lens in a group of five healthy subjects between the ages of 18 and 35 years. A parametric representation of the cross-sectional shape was fitted to the edges of the lens, which were determined with a Canny edge filter. Based on a partition of the lens into eight parts, the parametric shape allowed calculation of the cross-sectional area, volume and surface area. Two accommodation stimuli were offered to the subjects in the MRI in order to study the changes with accommodation. Corrected Scheimpflug imaging was used to validate the results obtained with MRI.
No statistical difference in central anterior and posterior radius of curvature and thickness was found between the MRI and Scheimpflug measurements. In accordance with the Helmholtz accommodation theory, with increasing accommodation a reduction of anterior and posterior radius of curvature was measured. Furthermore, a decrease of equatorial diameter and an increase of lens thickness were found. Based on MRI, and partition of the lens into eight parts, the mean volume in the group of five healthy subjects was 160±2.5 mm3 and the volume showed no significant change (p=0.9) during accommodation (160±2.7 mm3). However, the mean surface area of the capsular bag showed a significant decrease (p=0.04) during accommodation from 176±2.8 to 168±2.9 mm2, equivalent to a mean strain of 5.0 %.
In the present study, the cross-sectional area of the lens increased with accommodation but no change of lens volume was found. This implies that the internal human lens material can be assumed to be incompressible and is undergoing elastic deformation. Furthermore, the change in surface area indicates that the capsular bag is also undergoing elastic deformation.
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