Image registration of the human accommodating eye demonstrates equivalent increases in lens equatorial radius and central thickness

AIM: To compare the results of in vivo human high resolution image registration studies of the eye during accommodation to the predictions of mathematical and finite element models of accommodation. METHODS: Data from published high quality image registration studies of pilocarpine induced accommodative changes of equatorial lens radius (ELR) and central lens thickness (CLT) were statistically analyzed. RESULTS: The mean changes in ELR and CLT were 6.76 mu m/diopter and 6.51 mu m/diopter, respectively. The linear regressions, reflecting the association between ELR and accommodative amplitude (AA(ELR)) was: slope=6.58 mu m/diopter, r(2)=0.98, P<0.0001 and between CLT and AACLT was: slope=6.75 mu m/diopter, r(2) =0.83, P<0.001. On the basis of these relationships, the CLT slope and the AA(ELR) were used to predict the measured change in ELR (ELRpredicted) There was no statistical difference between ELRpredicted and the measured ELR as demonstrated by a Student's paired t-test: P=0.96 and linear regression analysis: slope=0.97, r(2) =0.98, P<0.00001. CONCLUSION: Image registration with invariant positional references demonstrates that ELR and CLT equivalently minimally increase similar to 7.0 mu m/diopter during accommodation. The small equivalent increases in ELR and CLT are associated with a large accommodative amplitude. These findings are consistent with the predictions of mathematical and finite element models that specified the stiffness of the lens nucleus is the same or greater than the lens cortex and that accommodation involves a small force (<5 g).