Measuring flap thickness crucial to LASIK effectiveness, study suggests

DALLAS — In vivo confocal microscopy showed significant variation in LASIK flap thickness in a study done here. Flaps created with two types of microkeratome in the study were on average significantly thinner than intended.

The study authors, from the University of Texas Southwestern Medical Center, said their findings emphasize the importance of performing intraoperative thickness measurements in LASIK and the usefulness of confocal microscopy for that purpose.

Fusun Gokmen, MD, and colleagues compared measurements of achieved vs. intended flap thickness with two Bausch & Lomb microkeratomes, the Automated Corneal Shaper and the Hansatome.

Twenty-seven eyes of 27 patients were examined using in vivo confocal microscopy through-focusing (CMTF) 3 to 12 months after LASIK. Twelve patients underwent LASIK with the ACS and 15 with the Hansatome. The researchers scanned the central cornea using CMTF and measured the epithelium, flap, stroma and corneal thickness. Normalized flap thickness was also calculated to account for changes in epithelial thickness that may have occurred postoperatively.

Posterior stromal thickness ranged from 233 µm to 431 µm in the ACS group and 258 µm to 382 µm in the Hansatome group. The mean non-normalized flap thickness was 133 µm in the ACS group and 167 µm in the Hansatome group. The mean normalized flap thickness was 130 µm in the ACS group and 158 µm in the Hansatome group.

Both microkeratomes cut significantly less than predicted (P < .05). The ACS cut a thinner-than-intended thickness in all cases while the Hansatome cut thicker-than-intended flaps in 13% of cases.

When comparing the two microkeratomes, the Hansatome showed significantly greater variability in flap thickness than the ACS (P < .05), the authors said.

The study is published in the June issue of the Journal of Cataract & Refractive Surgery.