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Gustavo R. Pinto, Eliane M. Nakano, Eduardo J. Simon, Luiz A. Melo, Jr., Paulo Schor; Corneal Ablation Profile In Refractive Surgery: Increase, Reduction Or Maintenance Of Spherical Aberration. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1498.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the behavior of spherical aberration under Conventional (CO), Wavefront Custom (CT) and Optimized Prolate (OP) myopic treatments.
In this multicenter retrospective study, 178 eyes were submitted to a primary mechanical LASIK using the Moria M2 microkeratome set to 160 µm for myopia and divided into 3 groups: CO (30 eyes), CT (132 eyes), and OP (16 eyes). CO and CT groups were operated on using Alcon Ladar 4000 excimer laser set to emmetropia under a default or wavefront guided ablation. OP was done using the Nidek EC 5000 excimer laser set to plane. Total wavefront was obtained within optical zone of 6.5 mm from Hartmann Shack sensor (LadarWave) in CO and CT groups. OPD-Scan was used for OP group. Spherical aberration was analyzed preoperatively and 3-month postoperatively. The spherical equivalent treated (SEt) in CO, CT, and OP groups ranged from -0.75 to -7.43 Spherical Diopters (SphD) (mean -3.84 ± 1.97 SphD), -0.35 to -6.91 SphD (mean -3.42 ± 1.35SphD), -0.25 to -6.12 SphD (mean 3.33 ± 1.72 SphD), respectively.
The change in spherical aberration related to SEt was statistically different (P<0.05) for the 3 groups. Conventional treatment resulted in a mean increase in spherical aberration among all evaluated range of +0.102 µm/SphD (R2=0.76, P<0.001). Wavefront Custom ablation presented linear decrease in spherical aberration for SEt from -0.35 to -1.85 SphD and linear increase from -2.0 to -6.91 SphD in the order of +0.096 µm for each diopter of SEt (R2=0.35, P<0.001). Optimized Prolate ablation showed reduction in spherical aberration among all evaluated range up to -5.75 SphD, although an increase trend could be shown in the order of +0.067µm/SphD (R2=0.36, P=0.013).
No treatment profile prevents increase in spherical aberration, but its progression is smaller in the OP than in the CT and CO treatments. If 0.35 microns of postoperative spherical aberration is to be used as a safety value for refractive surgery, than CT treatments should not be done after 3.50 diopters of SEt but OP needs to be used after that range. CO treatments resulted in spherical aberration superior to 0.35 μm.
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