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R. Sabesan, G. Yoon; Short-Term Visual Benefit of Correcting Higher Order Aberrations in Keratoconic Eyes. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2842.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate whether or not keratoconic eyes can achieve perfect visual performance when their ocular aberrations are corrected nearly to the diffraction-limit using large-stroke adaptive optics
An adaptive optics system equipped with a large-stroke deformable mirror and a Shack Hartmann wavefront sensor was used to correct the aberrations in 5 normal and 7 keratoconic eyes over a 6 mm pupil. Defocus and astigmatism were partially compensated using a Badal system and a phoropter in keratoconic eyes, prior to closed-loop correction, to conserve the dynamic range of the mirror. High deformable mirror gain was employed to ensure the stability of closed-loop correction. High contrast visual acuity was measured using tumbling letter ‘E’ test over a 6-mm pupil in both groups. Stable optical quality was provided with dynamic closed-loop adaptive optics during visual acuity test.
After adaptive optics correction, the average residual rms in normal and keratoconic eyes was 0.08 ± 0.025µm and 0.1 ± 0.015 µm respectively over a 6mm pupil and they were not significantly different (p = 0.174). High deformable mirror gain allowed rapid convergence of aberration correction within 3-5 iterations. In addition, it also helped to maintain a stable residual error during the visual acuity test. Averaged variability of dynamic correction performance, defined as the standard deviation of residual RMS during acuity test, was 0.025 ± 0.014 µm. The average high contrast visual acuity in normal eyes was -0.24 ±0.071 logMAR over a 6-mm pupil, while that in keratoconic eyes was -0.08±0.055 logMAR. Difference in visual acuity between keratoconic and normal eyes was observed to be statistically significant (p = 0.004).
With the same perfect optical quality, visual performance is significantly worse in keratoconic eyes compared to normal eyes. Long-term visual experience with poor retinal image quality, induced by higher order aberrations, may be restricting the visual benefit achievable immediately after correction in keratoconic eyes. However, maximum predicted visual performance might be expected in these eyes after long term adaptation of the visual system to near-diffraction limited ocular optics.
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