Comparison of intraoperative ultrasound pachymetry and postoperative optical coherence tomography of anterior segment in the measurement of flap thickness in eyes receiving laser in situ keratomileusis.

Abstract

To compare the measurement of flap thickness using intraoperative ultrasound pachymetry and postoperative Visante anterior segment optical coherence tomography (Visante-OCT) in eyes receiving laser in situ keratomileusis (LASIK). Seventeen patients (34 eyes) received LASIK using a Technolas-217Z100 laser and AMADEUSⅡ mechanical microkeratome (140μm head). Flap thickness was assessed with an ultrasound pachymeter intraoperatively and a Visante -OCT postoperatively at 1 week and 1 month. The intraoperative mean flap thickness by ultrasound pachymetry was (124±13.9) μm (range: 96.5 to 160 μm), and mean flap thickness by Visante-OCT was (145±7.13) μm (range: 130 to 158 μm) and (143±5.32) μm (range: 132 to 155 μm) postoperatively at 1 week and 1 month respectively (F =63.52, P<0.01). Intraoperative subtraction pachymetry underestimated flap thickness compared with postoperative Visante-OCT (P<0.01). There was no significant difference between postoperative Visante-OCT measurements at 1 week and 1 month after LASIK (P=0.16). The 95% limit of agreement (LoA) of flap thickness between ultrasound Visante-OCT and pachymetry was -5.40 to 42.10 μm. OCT overestimates flap thickness compared with intraoperative ultrasound pachymetry when using the AMADEUSⅡ mechanical microkeratome.