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Guang-ming G. Dai; Optical Zone Extension for Wavefront-Guided Refractive Surgery. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5773.
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To investigate the advantage and disadvantage of two optical-zone extension approaches
It is well known that low order ocular aberrations are independent of pupil size. Therefore, low order aberrations have been used to extend the optical zone to a larger diameter to alleviate night vision problems when ocular wavefront aberrations are captured at a smaller diameter. However, leaving the high order aberrations uncorrected for the extended annular zone may create additional concerns because high order aberrations naturally extends beyond the wavefront diameter. Zernike rescaling algorithm (JOSAA, vol 26, 539-543, 2006) is suggested to use for obtaining the aberrations beyond the originally captured diameter. Statistical analysis of two clinical studies (703 eyes and 130 eyes, respectively) is used to evaluate the error induced due to optical zone extension.
It has been shown from a multi-center clinical study (703 eyes) that the inter-exam ocular wavefront variability can exceed the error induced due to the rescaling of Zernike coefficients to a larger diameter in practical applications, especially when the change in pupil diameter is relatively small. For optical zone extension, two studies were conducted: (1) for 703 eyes having 6 mm wavefront captures, these wavefront maps are masked to 4 mm. Treatment targets for each eye with and without zone extension are calculated. The induction of the spherical aberration (SA) due to the zone extension is significant as shown in the figure below (left panel). (2) For 74 eyes in a separate study, 10 eyes were treated using zone extension (wavefront diameter from 5 mm to 5.75 mm) and the other 64 eyes were treated without zone extension (6 mm OZ was used for all eyes). The post-operative (3M-6M) SA was shown (right panel) as two cohorts. For the cohort having wavefront diameter smaller than 6 mm, it induces statistically significantly (p = 0.026) greater spherical aberration (0.187±0.168 µm) than the cohort having at least 6 mm wavefront diameter (0.099±0.124 µm).
Rescaling Zernike coefficients from a smaller pupil size to a larger one can have practical applications in optical zone extension for wavefront-guided refractive surgery
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