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Larger analysis diameter helps detect LASIK-induced aberrations
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Induced spherical aberration after LASIK may be best measured by using an analysis diameter larger than the original optical treatment zone, a group of researchers suggests.
James Andrew Hiatt, MD, and colleagues at Boxer Wachler Vision Institute in Beverly Hills, Calif., performed a study to try to determine acceptable parameters for wavefront measurement after LASIK. To do this, they conducted a retrospective chart review of 21 eyes of 12 patients who had undergone CustomCornea LASIK with the Alcon LADARVision 4000. The Moria M2 microkeratome 90 µm head was used in all procedures.
Preoperative spherical equivalents of the eyes ranged from –1.14 D to –7.64 D. Five of the eyes had less than 3 D of myopia, 12 were between –3 and –6 D and four had more than –6 D.
LASIK was performed using a 6.5-mm central optical zone and blend zone to 9 mm.
Wavefront analyses were performed before and 3 months after the surgery. Measurements were made at pupil diameters of 5.5, 6, 6.5 and 7 mm. The main outcome measures were spherical aberration, coma and other higher-order aberrations, and these were analyzed for the whole group as well as for low, medium and high myopes at each analysis diameter.
“CustomCornea wavefront-guided LASIK with a central 6.5-mm optical zone was shown not to induce coma and other aberrations at all four pupil analysis diameters,” the researchers reported in the June issue of Ophthalmology. The only group to show a statistically significant increase in spherical aberration was the high correction group.
“From these findings, eyes with pupils up to 7 mm and correction up to –6 D can be treated with CustomCornea LASIK without significant induction of spherical aberration. Eyes with more than 6 D of myopia and pupils that do not expand beyond the 6.5-mm optical zone can be treated without induction of significant spherical aberration,” the study authors said.
They concluded that, in order to detect larger degrees of induced spherical aberration, analysis diameters of 0.5 mm larger than the optical treatment zone should be considered.
Limitations to the study included the sample size and the single laser system used in the surgery, the authors noted.