Aspheric Optical Zones: The Effective Optical Zone with the SCHWIND AMARIS.

PURPOSE

To evaluate the effective optical zone (the part of the ablation that receives full correction) among eyes that underwent laser epithelial keratomileusis (LASEK)/epi-LASEK treatments for myopic astigmatism.

METHODS

Twenty LASEK/epi-LASEK treatments with a mean spherical equivalent refraction (SE) of -5.49±2.35 diopters (D) performed using the SCHWIND AMARIS system were retrospectively evaluated at 6-month follow-up. In all cases, pre- and postoperative corneal wavefront analyses were performed with the Keratron Scout (OPTIKON 2000). Effective optical zone values were evaluated from the changes of root-mean-square (RMS) of higher order wavefront aberration (ΔRMSho), spherical aberration (ΔSphAb), and RMS of the change of higher order wavefront aberration (RMS[ΔHOAb]). Correlations of effective optical zone with planned optical zone and SE correction were analyzed using a bilinear function as well as calculations of the isometric lines for which effective optical zone equals planned optical zone and of the nomogram planned optical zone to achieve an intended effective optical zone.

RESULTS

At 6 months, SE was -0.05±0.43 D, with 90% of eyes within ±0.50 D. Mean higher order wavefront aberration RMS increased 0.12 μm, spherical aberration 0.09 μm, and coma 0.04 μm after treatment (6-mm diameter). Mean planned optical zone was 6.76±0.25 mm, whereas mean EOZ(ΔRMSho) was 6.74±0.66 mm (bilinear correlation P<.005), EOZ(ΔSphAb) was 6.83±0.58 mm (bilinear correlation P<.0001), and EOZ(RMS(ΔHOAb)) was 6.42±0.58 mm (significantly smaller, P<.05; bilinear correlation P<.0005).

CONCLUSIONS

The EOZ(ΔRMSho) and EOZ(ΔSphAb) were similar to the planned optical zone, whereas EOZ(RMS(ΔHOAb)) was significantly smaller. Differences between effective optical zone and planned optical zone were larger for smaller planned optical zone or larger SE corrections. Planned optical zones >6.75 mm result in effective optical zones at least as large as planned optical zones. For optical zones <6.75 mm, a nomogram should be applied.