Impact of head advance and oscillation rate on the flap parameter: a comparison of two microkeratomes

To compare flap quality and thickness in an experimental setting using the Amadeus and Carriazo/Barraquer microkeratomes.

One hundred and sixty-three fresh porcine cadaver eyes were used to cut corneal flaps. One hundred and thirty-five eyes were cut using the Amadeus microkeratome with various settings of head advance and oscillation rate, 28 eyes using the Carriazo/Barraquer microkeratome (Supratome). Flap diameter and hinge width were measured by planimetry and flap thickness by ultrasound pachymetry. Descriptive statistical analysis was based on medians and quartiles, graphical representation on box plots. The measurement devices were compared by two sample Wilcoxon tests, their deviation from the distributors' reference measurement values by sign tests.

Variation of oscillation rate and head advance led to significant differences in flap thickness. Optimal cut quality was achieved with 1 mm/s head advance and 8,000 rpm in the Amadeus microkeratome. With this setting the smallest target deviations in flap thickness were obtained among the results with lowest range (median 170 micro m, interquartile range 18 micro m, target 160 micro m). The Amadeus microkeratome demonstrated a statistically significant lower deviation from the target thickness ( P<0.001) and also a lower range than the Supratome (median 127 micro m, interquartile range 30 micro m, target 140 micro m; P<0.001).

Optimization of microkeratome settings leads to minimized deviation from target thickness and improved parameter. The Amadeus microkeratome achieved a statistically significant lower deviation in flap thickness than the Carriazo/Barraquer microkeratome. Individualization of the microkeratome settings may help to decrease flap complications and improve refractive outcome.