Calculating Accommodative Optical Response in Young and Pre-presbyopic Eyes using Paraxial Schematic Eye Models

Abstract

Purpose: Ultrasound biomicroscopy (UBM) studies on young and pre-presbyopic subjects show that the accommodative optical response (AOR) can be predicted in a population from each UBM measured biometry parameter using linear relationships between AOR and accommodative biometric changes, with standard deviations of less than 0.55 D. Here, ocular biometry parameters measured for different accommodative states were used to construct accommodating paraxial schematic eyes (SE) to predict the AOR.

Methods: The ocular parameters measured were corneal thickness, anterior and posterior corneal radii of curvature (from OCT), anterior chamber depth, lens thickness, anterior and posterior lens radii of curvature (from UBM) and axial length (from A-scan ultrasound). UBM parameters were measured while subjects accommodated to different stimulus demands. The AOR to the same stimulus demands was measured objectively with a Grand-Seiko (GS) autorefractor. Subjects included 24 young and 24 pre-presbyopes. Paraxial SE models were constructed for all subjects for all accommodative states. Standard and iteratively calculated lens equivalent refractive index values were used. Individual SE models were also constructed for all subjects using the average change in each UBM parameter for each stimulus demand from the baseline unaccommodated state in each subject population. The AOR calculated from the SE models were compared with the GS measured AOR from each subject.

Results: The slopes and r² values of the linear regressions between individual schematic eye calculated and GS measured AOR for the young subjects were 0.77 and 0.86 and for the pre-presbyopic subjects were 0.64 and 0.55. The mean difference in AOR (GS - individual SEs) was -0.27 D for the young subjects and 0.33 D for the pre-presbyopic subjects. In the individual eyes, the mean ± SD of the absolute differences in AOR between the GS and SEs for the young and pre-presbyopic subjects was 0.50 ± 0.39 D and 0.50 ± 0.37 D, respectively. For average SEs, the mean ± SD of the absolute differences in AOR between the GS and the SEs for the young and pre-presbyopic subjects was 0.77 ± 0.88 D and 0.51 ± 0.49 D, respectively.

Conclusions: Individual paraxial SE models calculated from measured ocular biometry parameters offer better prediction of AOR than from individual biometry parameters in young and pre-presbyopic subject populations.