Flap analysis: critical point in laser in situ keratomileusis

A prospective study of 151 eyes, which underwent laser in situ keratomileusis, was done. Corneal flap creation was performed by using Moria LSK- One microkeratome (160 micrometers thickness) (distributed by Microtech, Inc., Moria, France). Flap thickness (measured by high frequency ultrasound), flap diameter (both horizontal and vertical), hinge size and pupillary hinge distance were recorded. The actual values from the measurement were compared to the predicted values from the microkeratome. The mean flap thickness was 161 +/- 38 micrometers compare to 160 micrometers predicted value. The mean diameter of the flap was 9.00 +/- 0.64 mm vertical and 8.94 +/- 0.54 mm horizontal compare to 9.00 mm predicted value. The hinge size was 4.75 +/- 0.84 mm. The pupillary-hinge distance was 3.35 +/- 0.61 mm. There was very high variable of the flap thickness, which can lead to miscalculation of the residual stroma. This miscalculation will be very critical if the residual stroma is left too thin. Caution should be made in higher level of myopia to avoid the serious complication such as keratectasia.