[Analysis of flap thickness created with mechanical microkeratome in LASIK by using anterior segment optical coherence tomography]

To evaluate the accuracy, uniformity and relevant factors of LASIK flaps created with a mechanical microkeratome Moria II (90, 110 and 130 heads).It was a case-control study. Eighty-seven patients underwent LASIK in both eyes using Moria II 90 head (52 eyes, 26 cases), 110 head (58 eyes, 29 cases), or 130 head (64 eyes, 32 cases). One week after surgery, anterior segment optical coherence tomography was performed four times on each eye to measure flap thickness at 20 points in four meridians. The results were assessed for accuracy, uniformity and relevant factors.The central thickness of corneal flaps was (119.23±15.65), (140.42±12.26), and (165.92±17.00) µm by Moria II 90, 110 and 130 heads, respectively. The shape of the corneal flaps in the three groups resembled a concave lens, the central zone was significantly thinner than the paracentral and peripheral zones. The central flap thicknesses were statistically significantly more accurate and regular than the flap in the peripheral zone (F=212.419, P0.05). The mean difference of right eye (19.58±0.44) µm was higher than that of the left eye (16.55±0.44) µm. The mean difference of knife in-side (21.30±0.55) µm was higher than the knife out-side (14.36±0.64) µm (F=25.341, 44.461; P0.05).The central flap thicknesses were more accurate as compared with the expected value. The mean flap thickness in the three groups was not uniform. Variation of the thickness in corneal flaps was greater in thicker flaps. The flap thickness in right eye was greater than that in left eye, according to the surgical sequence between two eyes. The flap thickness of blade in-side was thicker than that of out-side.