OCT easily measures corneal flap thickness accurately

Dr. Coskunseven, who is director, refractive surgery department, Dunya Eye Hospital, Istanbul, Turkey, and colleagues evaluated the predictability and reproducibility of the flap thickness using the femtosecond laser and OCT.

Flap thickness measurements

Dr. Coskunseven reported that 30 days after surgery in the 90-µm group, the 12 eyes had a mean flap thickness of 98.2 ± 12.0 µm (range, 72 to 115 µm); in the 100-µm group, the 24 eyes had a mean flap thickness of 106.4 ± 12.5 µm (range, 78 to 142 µm); in the 110-µm group, the 30 eyes had a mean flap thickness of 115.2 ± 14.5 µm (range, 88 to 145 µm); and in the 120-µm group, the 30 eyes had a mean flap thickness of 130.4 ± 13.4 µm (range, 105 to 151 µm).

When the investigators compared the flap thicknesses 30 days after surgery with the thicknesses before the flaps were lifted, they found that the mean differences between the two time points were very small. In the 90-, 100-, 110-, and 120-µm groups, the mean differences from 30 days after surgery were 8, 7.2, 4.4, and 4.6 µm, respectively.

He also demonstrated on an OCT cross-section image the uniformity of a representative cornea at nine measurement points. "In the 90-µm group, the standard deviation was 3.00 µm, in the 100-µm group, 3.38 µm, in the 110-µm group, 3.30 µm, and in the 120-µm group, 3.77 µm," he stated.

A comparison among the 10-, 15-, 30-, and 60-kHz femtosecond lasers showed that the 60-kHz laser, which was used in the study under discussion, created flaps in all four groups that were closer to the desired thickness than did the other powers of the femtosecond laser.

"OCT is a very easy, noninvasive, accurate procedure for measuring flap thickness. Creating a flap with the IntraLase femtosecond 60 laser is a more predictable and reproducible procedure and OCT shows the uniformity of the flap thickness," Dr. Coskunseven concluded.