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S. Kasthurirangan, E. Markwell, D. A. Atchison, J. M. Pope, G. Smith; Magnetic Resonance Imaging Study of Crystalline Lens Shape With Accommodation and Age. Invest. Ophthalmol. Vis. Sci. 2007;48(13):6008.
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© ARVO (1962-2015); The Authors (2016-present)
Magnetic resonance imaging can provide high resolution in-vivo images of the whole crystalline lens. This method avoids two problems in past studies of crystalline lens shape, namely optical distortions and in-vitro post-mortem changes. The objective of this study was to compare changes in surface profile of the crystalline lens with accommodation and age using in-vivo magnetic resonance imaging.
Magnetic resonance images along the sagittal and axial planes were obtained for one eye each of 12 young (18-27 years) and 11 older (59-67 years) subjects when viewing at far (~6 m) and additionally at individual near points in the young subjects. Crystalline lens parameters measured were a) axial thickness, b) equatorial diameter and c) radius of curvature & asphericity of anterior and posterior lens surfaces. Global lens shape indices were calculated as the ratio of axial thickness to equatorial diameter (AT/ED) and ratio of anterior to posterior radii of curvature (AR/PR). Statistical testing was done with paired t-test for accommodation and two-sample t-test for age.
Only results from axial images are presented. With accommodation, lens thickness increased by 0.34 mm (p<0.05), diameter decreased by 0.33 mm (p<0.05) and radii of curvature decreased (anterior change: 4.12 mm, p<0.05; posterior change: 0.55 mm, p<0.05). Anterior surface became less oblate (change in asphericity: -4.01, p<0.05), while posterior surface asphericity did not change and remained prolate (p=0.96). With age, lens thickness increased by 1.02 mm (p<0.05) and diameter increased by 0.38 mm (p<0.05). Radius of curvature of the anterior surface decreased by 3.81 mm (p<0.05) but posterior lens radius of curvature did not change (p=0.20). The anterior lens became less oblate (change in asphericity: -4.45, p<0.05) and posterior lens changed from prolate to sphere (change in asphericity: +0.82, p<0.05). Shape indices were different between unaccommodated young and old lenses (p<0.05 for each index) and between accommodated young and unaccommodated old lenses (p<0.05 for AT/ED; p=0.05 for AR/PR).
The findings support the Helmholtz theory of accommodation including a clear decrease in the radius of curvature of the posterior lens. Accommodation and age cause similar changes in the anterior lens surface, while changes in the posterior surface and global shape indices were not similar, suggesting different effects of accommodation and age on the antero-posterior symmetry of the crystalline lens.
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