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To identify adjustments in manifest sphere and cylinder treatment to compensate effects of treating higher order aberrations (Zernicke Polynomials C6-C27) to optimize topography-guided LASIK outcomes. We hypothesize C11 and C13 (high order astigmatism) should affect cylinder treatment similar to C12 (spherical aberration) with spherical treatment.
Data from 500 eyes (out of a planned 1,000) which underwent topography-guided LASIK using the EX500 (Alcon, Fort Worth, TX) for C6-C27 was analyzed using regression analysis and non-linear optimization to assess whether programmed cylinder and spherical treatments should be adjusted to minimize post-operative refractive error at 1-month. Additionally, differences between manifest cylinder and Vario estimated cylinder at the axes of 0/90 and 45/135 degrees were compared against C7 and C8 (coma) as well as C11 and C13.
C11 is associated with directional difference in manifest and Vario cylinder at 45/135 degrees (regression coefficient: 1.30 ± 0.27, P < 0.001). C13 is associated with directional difference in manifest and Vario cylinder at 0/90 degrees (0.98 ± 0.30, P = 0.001). C7 and C8 are not significantly associated with cylinder directional differences (P = 0.68, 0.31) nor absolute vector differences (P= 0.44, 0.28) at the axes of 45/135 and 0/90. In surgical nomogram optimization, no variables were significantly correlated with cylinder change at either 0/90 or 45/135 degrees. C12 was found to be significantly correlated with spherical change (-0.70 ± 0.32, P = 0.03).
Adjustments to cylinder treatment to compensate C11 and C13 may be helpful based on the significant association with the difference in Vario and manifest refraction. Data from surgical outcomes is not conclusive but may be complicated by surgical result variability and post-operative refraction error reducing correlations.