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Ying Wu, Ji He, Xingtao Zhou, Renyuan Chu; A limitation of Hartmann-Shark system in measuring wavefront aberrations for patients received laser refractive surgery. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3118.
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When a Hartmann-Shark aberrometer was used to measure wavefront aberrations for patients received laser refractive surgery, the effective pupil size of the measurement was often smaller than the real pupil size. In this study, relationship between the effective pupil size and ablation parameters was tested for a group of myopic patients in order to investigate the limitation of the Hartmann-Shack aberrometer in measuring post-operative wavefront aberrations.
58 subjects (95 eyes) received myopic LASIK were tested for manifest refraction, Hartmann-Shark aberrometry (Carl Zeiss Meditec, Germany) and Pentacam scanning (OCULUS, Germany). Wavefront aberrations were measured under mydriatic condition (pupil size>8.0mm), and the effective pupil size was directly provided from the aberrometer. Spherical error of ablation (Rx), depth of ablation, optical zone of ablation (OZ) and corneal eccentricity (E value) were obtained from surgical records. Pearson correlation and multiple stepwise regression analyses were performed to test relationship between the effective pupil size and each ablation parameter.
For all patients, the effective pupil size was smaller than their real pupil size with a mean of 6.90±0.53mm (n=15, t=3.0, p<0.01), 6.56±0.37mm (n=26, t=8.3, p<0.0001), and 5.84±0.55mm (n=54, t=14.7, p<0.0001) for mild, moderate and high myopia respectively. The effective pupil size was significantly correlated to the Rx of ablation (r=-0.80, p<0.0001), the depth of ablation (r=0.65, p<0.0001), the OZ of ablation (r=0.70, p<0.0001), and the postoperative corneal E value (r=0.57, p<0.0001). Regression analysis revealed that Rx of ablation, OZ of ablation, and postoperative E value were the independent factors, with a model of the effective pupil size= -0.81*Rx of ablation+1.11*OZ of ablation+0.55*postoperative E value (r2 =0.997).
Effective pupil size of Hartmann-Shark wavefront measurements for patients with laser refractive surgery is systematically reduced with its size reduction linearly related to refractive error, ablation optical zone and corneal eccentricity. The Hartmann-Shack system is limited in measuring post-operative wavefront aberrations for whole pupil area, and therefore it provides underestimates of wavefront aberrations for post-operative eyes.
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