Factors that affect corneal flap thickness with the Hansatome microkeratome

To evaluate factors that influence corneal flap thickness with the Hansatome microkeratome.

One hundred thirty-two eyes of 70 patients underwent laser in situ keratomileusis (LASIK). Corneal flap thickness was measured by subtracting the intraoperative corneal bed pachymetry measurement from intraoperative total corneal pachymetry. Variables examined included plate thickness, ring size, blade use, temperature, humidity, barometric pressure, age, average keratometric power, and preoperative corneal thickness.

Mean flap thickness using a 180-microm plate was 143 +/- 19 microm (range 61 to 207 microm). Mean flap thickness using a 160-microm plate was 119 +/- 20 microm (range 83 to 159 microm). The difference was statistically significant (P < .05). Mean flap thickness using a 180-microm plate and the same blade on the right and left eye was 151 +/- 21 microm (range 113 to 200 microm) and 137 +/- 21 microm (range 91 to 191 microm), respectively. The 14-microm difference was statistically significant (P < .001). There was a slight negative correlation of flap thickness with humidity. There was a positive correlation with preoperative corneal thickness (pachymetry).

The Hansatome tended to cut thinner flaps than anticipated based on the plate used. Flaps cut on the first eye were thicker than the second eye using the same blade. Thicker corneas tended to lead to thicker flaps. There was no correlation between flap thickness and microkeratome ring size, temperature, barometric pressure, patient age, or average keratometric power.