In vivo study of changes in refractive index distribution in the human crystalline lens with age and accommodation.

PURPOSE Magnetic resonance imaging (MRI) was used to map the refractive index distribution in human eye lenses in vivo and to investigate changes with age and accommodation. METHODS Whole-eye MR images were obtained for sagittal and transverse axial planes in one eye each of 15 young (19-29 years) and 15 older (60-70 years) subjects when viewing a far ( approximately 6 m) target and at individual near points in the young subjects. Refractive index maps of the crystalline lens were calculated by using a procedure previously validated in vitro. RESULTS A central high refractive index plateau region and sharp decline in refractive index at the periphery were seen in all three groups. The peripheral decline was steepest in the older lenses and least steep in the young accommodated lenses. Average lens thickness increased (+0.27 mm; P < 0.05) and equatorial diameter decreased (-0.35 mm; P < 0.05) with accommodation. Axial thickness (+0.96 mm; P < 0.05) and equatorial diameter (+0.28 mm; P < 0.05) increased with age. The central index (1.409 +/- 0.008) did not differ between groups. The axial thickness of the central plateau increased with age (+0.83 mm; P < 0.05) but not significantly with accommodation. The equatorial diameter of the central plateau increased with age (+0.56 mm; P < 0.01) and decreased with accommodation (-0.43 mm; P < 0.05). CONCLUSIONS The refractive index of the central plateau region does not change significantly with accommodation or ageing, but its size increases with age and the peripheral decline in refractive index becomes steeper in older lenses.