Correcting Highly Aberrated Eyes Using Large-Stroke Adaptive Optics

Abstract

Purpose:: To investigate the optical performance of a large-stroke deformable mirror in correcting large amounts of aberrations in highly aberrated eyes

Methods:: A large-stroke deformable mirror (Imagine Eyes: MIRAO-52D) and a Shack-Hartmann wavefront sensor were used in an adaptive optics system. Individual Zernike modes up to the 5^th order with varying amplitudes were produced using the mirror. Closed-loop correction of the static aberrations of a phase plate, designed for an advanced keratoconic eye, was performed for a 6mm pupil. The same adaptive optics was also used to correct the aberrations in 3 keratoconic (1 advanced and 2 moderate) and 3 normal eyes for a 6mm pupil. Defocus and astigmatism were partially compensated using a Badal system and a phoropter in the highly aberrated eyes, prior to closed-loop correction, to conserve the dynamic range of the mirror. The residual aberrations were averaged over 5 seconds after correction to determine the overall corrective performance.

Results:: The influence functions of the actuators as a function of the applied voltage showed 99.99% linearity. The maximum strokes measured for central and peripheral actuators were 38.43 µm and 27.36 µm in wavefront, respectively. This large dynamic range of the mirror allowed individual 2^nd order Zernike modes up to 7 µm RMS, 3^rd order modes up to 5 µm RMS, 4^th order modes up to 2 µm RMS and 5^th order modes up to 0.5µm RMS to be accurately produced with negligibly small error. In closed-loop correction, the total RMS of the phase plate over a 6mm pupil was reduced from 3.54 µm to 0.038 µm in 10-15 iterations, corresponding to 1-1.5 seconds. The 3 normal eyes had an average total RMS (higher order RMS) of 1.78 ± 0.86 µm (0.32 ± 0.14 µm) and 0.089 ± 0.01 µm (0.05 ± 0.01 µm), before and after closed-loop correction respectively. For the 3 keratoconic eyes, that have higher amplitudes of higher order aberrations, adaptive optics reduced an average total RMS (higher order RMS) of 3.54 ± 1.79 µm (2.71 ± 1.42 µm) to 0.23 ± 0.11 µm (0.17 ± 0.13 µm) in closed loop correction.

Conclusions:: Aberrations in both normal and highly aberrated eyes were successfully corrected using the large-stroke deformable mirror. This mirror can be a powerful tool to assess the limit of visual performance achievable after correcting the aberrations, especially in eyes with abnormal corneal profiles.

Keywords: optical properties • keratoconus