LASIK flap thickness profile and reproducibility of the standard vs zero compression Hansatome microkeratomes: three-dimensional display with Artemis VHF digital ultrasound

Abstract

Purpose: To measure the mean flap thickness profile and calculate accuracy and reproducibility for standard and zero compression Hansatome microkeratomes (Bausch & Lomb).

Methods: Retrospective study of 99 myopic eyes (51 patients) after LASIK using the standard or zero compression Hansatome microkeratomes (160-μm head). Reinstein Flap Thickness was calculated as preoperative epithelial thickness plus postoperative stromal component of the flap as measured by Artemis VHF digital ultrasound (ArcScan Inc). Mean and standard deviation flap thickness were calculated and plotted for a 10-mm diameter. Accuracy was calculated as the difference between the mean and intended flap thickness. Reproducibility was evaluated as the flap thickness standard deviation between eyes. Multivariate regression was performed for flap thickness against surgery order, atmospheric/vacuum pressure difference, spherical equivalent refraction, pachymetry, and keratometry.

Results: For both Hansatome models, the mean flap thickness profile showed a thinnest region inferotemporally and thicker in the periphery of the inferotemporal edge and nasally. Mean central flap thickness was 140.3±17.5 μm (accuracy: -19.7 μm) and 119.0±12.7 μm (accuracy: -41.0 μm) for standard and zero compression Hansatomes, respectively. Eyes treated second were thinner (15.4 μm and 12.6 μm thinner for standard and zero compression Hansatomes, respectively). Multivariate regression improved the reproducibility to 14.8 μm (P<.05; surgery order, pachymetry) and 9.4 μm (P<.05; surgery order, atmospheric/vacuum pressure difference) for standard and zero compression Hansatomes, respectively.

Conclusions: The flap thickness profiles were similar for standard and zero compression Hansatomes characterized by a thinnest region inferotemporally, rather than a meniscus shape as has been suggested previously. The zero compression Hansatome created thinner, more reproducible flaps. Surgery order and atmospheric/vacuum pressure difference might be used to obtain thinner flaps using a Hansatome.