Evaluation of High Spatial Frequency Wavefront Aberrations in the Eye

Abstract

Abstract: : Purpose: Wavefront aberrometers have identified low spatial frequency variations that result in a significant refraction change with pupil position. However, instrument resolution has limited our ability to evaluate higher spatial and temporal frequency aberrations. The purpose of this work is to evaluate the spatial structure of refractive error across the pupil and to separate the temporal from the permanent or static aberrations. Methods: We modified a COAS aberrometer with a special high-density lenslet array wavefront sensor to obtain over 3500 data points across the pupil. The aberrometer was configured to acquire data at a high rate for long periods. Data could be recorded at 15 or 30 Hz for up to 1 min total. The instantaneous aberration information was averaged to produce the static wavefront aberration, and the average was subtracted from individual frames to study the temporal characteristics. In addition, the high spatial frequency structure was examined by subtracting the low order aberrations (through 4th order) from the wavefront. Results: The aberration structure was observed to have both random and systematic components. In one case study we observed 0.17 µm RMS wavefront error that was a fixed structure, with the low order (up to 4th order) aberrations subtracted. The time-dependent part during the same period had wavefront fluctuations of 0.045 µm RMS. The total aberrations for this eye were 0.73 µm RMS. Conclusions: Both the temporal and spatial wavefront aberration fluctuations were observed in a normal eye. Evaluation of these higher order effects is important if they are used for customized Lasik ablation or other correction method. Both the 0.45 µm RMS fluctuation and the 0.17 µm RMS higher order aberration could not be corrected by any of the current generation of surgical lasers. Yet these results would have been included in measurements made at lower spatial or temporal resolution.  

Keywords: refractive surgery: optical quality • refractive surgery: other technologies • optical properties