Evaluation of the performance of accommodating IOLs using a paraxial optics analysis

Abstract

Purpose: We employed an analytical approach to evaluate the key parameters for the potential design optimisation of accommodating intra-ocular lenses (AIOL) and to use these parameters to predict their accommodative performance.

Methods: Paraxial thin-lens equations to predict the accommodative performances of single-element (1E) and two-element (2E) AIOLs were developed. 2E-AIOLs with either mobile front or back lens elements were analysed as well as 1E-AIOL for their accommodative performance. A paraxial model including key ocular components (corneal surfaces, pupil and retina) as well as AIOL was used to evaluate the key control parameters and optimal design configurations. A range of variants of the model, representing varying powers of front and back optical elements and with either front or back optical element mobile was tested.

Results: Optimal accommodative performance of 2E-AIOL is governed by the power combinations of its optical elements; design variants with higher positive front element power produced greater accommodative efficacy, while mobility of the front element contributed more to the accommodative performance than the back element. The performance of 1E-AIOL is primarily governed by the power of the AIOL; the higher the AIOL power, the better the accommodative performance.

Conclusions: From an accommodative performance standpoint, the optimal design of 2E-AIOL should comprise a high plus power front element. Considering the maximum potential amounts of element translation available clinically, 2E-AIOLs are predicted to offer higher accommodative performance compared to 1E-AIOL.

Figure 1

Paraxial optics prediction of change in accommodation (D) with axial position of the mobile element for seven design variants (different front and back element power) of a two-element 2E-AIOL with (a) Configuration 1 (mobile front element) and (b) Configuration 2 (mobile back element). For both (a) and (b), power of the front element is indicated by the labels. Solid line represents the variant corresponding to a 1E-AIOL and long dashed line represents the variant portraying an immobile (single-vision) IOL. Accommodation in negative scale indicates de-accommodation (decrease in power) with element translation.

Figure 2

Accommodative performance (dK/dZ) of a 2E-AIOL of (a) Configuration 1 with mobile front element and (b) Configuration 2 with mobile back element versus mobile element power (front power F_f for Configuration 1, back power F_b for Configuration 2). Practically, good accommodative performance can be achieved more efficiently with positive power front elements and/or negative power back elements. Otherwise, an extremely high negative power front, or positive power back, element is required to produce a matching amount of accommodation. Between the two zero-points, forward (Configuration 1) or backward (Configuration 2) translation results in de-accommodation.

Figure 3

A plot of accommodative performance (dK/dZ) versus total IOL power (F_iol) for 1E-AIOL. Good performance can be achieved more efficiently for higher positive power of the AIOL reaching a maximum when it is equal to the equivalent dioptric value of the vitreous chamber depth.