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Operator-induced errors in Hartmann-Shack wavefront sensing: Model eye study.

Cervino A, Hosking SL, Dunne MC

From the School of Life and Health Sciences (Cervino, Hosking, Dunne), Aston University, United Kingdom, and the School of Optics and Optometry (Cervino), Universidad de Santiago de Compostela, Spain.

PURPOSE: To evaluate the effects of instrument realignment and angular misalignment during the clinical determination of wavefront aberrations by simulation in model eyes. SETTING: Aston Academy of Life Sciences, Aston University, Birmingham, United Kingdom. METHODS: Six model eyes were examined with wavefront-aberration-supported cornea ablation (WASCA) (Carl Zeiss Meditec) in 4 sessions of 10 measurements each: sessions 1 and 2, consecutive repeated measures without realignment; session 3, realignment of the instrument between readings; session 4, measurements without realignment but with the model eye shifted 6 degrees angularly. Intersession repeatability and the effects of realignment and misalignment were obtained by comparing the measurements in the various sessions for coma, spherical aberration, and higher-order aberrations (HOAs). RESULTS: The mean differences between the 2 sessions without realignment of the instrument were 0.020 mum +/- 0.076 (SD) for Z(3)(-1)(P = .551), 0.009 +/- 0.139 mum for Z(3)(1)(P = .877), 0.004 +/- 0.037 mum for Z(4)(0) (P = .820), and 0.005 +/- 0.01 mum for HO root mean square (RMS) (P = .301). Differences between the nonrealigned and realigned instruments were -0.017 +/- 0.026 mum for Z(3)(-1)(P = .159), 0.009 +/- 0.028 mum for Z(3)(1) (P = .475), 0.007 +/- 0.014 mum for Z(4)(0)(P = .296), and 0.002 +/- 0.007 mum for HO RMS (P = 0.529; differences between centered and misaligned instruments were -0.355 +/- 0.149 mum for Z(3)(-1) (P = .002), 0.007 +/- 0.034 mum for Z(3)(1)(P = .620), -0.005 +/- 0.081 mum for Z(4)(0)(P = .885), and 0.012 +/- 0.020 mum for HO RMS (P = .195). Realignment increased the standard deviation by a factor of 3 compared with the first session without realignment. CONCLUSIONS: Repeatability of the WASCA was excellent in all situations tested. Realignment substantially increased the variance of the measurements. Angular misalignment can result in significant errors, particularly in the determination of coma. These findings are important when assessing highly aberrated eyes during follow-up or before surgery.

Published 26 December 2006 in J Cataract Refract Surg, 33(1): 115-21.
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