Changes in lens dimensions and refractive index with age and accommodation

Purpose. To measure changes in human eye lens dimensions and refractive index with age and state of accommodation. Methods. MRI methods were used to measure refractive index maps and lens geometry (diameter and thickness) of an axial slice through the lens in 44 volunteers aged 18 to 59 years, with an accommodation stimulus of 0.17 D (unaccommodated state). In a subpopulation of 26 young volunteers aged 18 to 33 years, lens dimensions were also measured in an accommodated (6.67 D stimulus) state. For a subpopulation of six of the young volunteers (22 to 33 years), refractive index maps were also acquired with an accommodation stimulus of 6.67 D. Results. Unaccommoclated lens thickness increased significantly with age (T = 3.31 +/- 0.10 mm + 0.0180 +/- 0.0036 mm X Age; p < 0.0001). Lens diameter (D = 9.33 +/- 0.0033 mm) and central refractive index (n(c) = 1.4198 +/- 0.0067) showed no significant age dependence. Lens thickness increased (Delta T = 0.050 +/- 0.024 mm/D) and diameter decreased (Delta D = -0.067 +/- 0.030 mm/D) on accommodation. A slight decrease in central refractive index with accommodation was not statistically significant. Conclusions. The results are consistent with the Helmholtz theory of accommodation.