RESUMEN
PURPOSE: To study changes in flap thickness made with two different microkeratome heads across different corneal locations using anterior segment optical coherence tomography (OCT). METHODS: In this prospective, non-randomized, consecutive case series, subjects who had their laser in-situ keratomileusis (LASIK) flaps made using 90 µm (MSU90) or 130 µm (MSU130) disposable M2 microkeratome heads were examined using OCT. The measurements were performed at three locations (central and 2.5 mm to either side) at 1 day, 1 week, and 1 month postoperatively. RESULTS: The central flap thickness was 123 ± 15, 130 ± 14, and 127 ± 13 µm, respectively, at 1 day, 1 week, and 1 month postoperatively in the MSU90 group (41 eyes) and 142 ± 20, 147 ± 19, and 143 ± 15 µm, respectively, in the MSU130 group (47 eyes). At 1 month, peripheral flap thickness was 161 ± 17 and 159 ± 13 µm, respectively, at 2.5 mm to the right and left of corneal center in the MSU90 group. The corresponding figures were 170 ± 14 and 167 ± 13 µm, respectively, in the MSU130 group. There was a statistically significant difference between the two groups at all locations (P < 0.001). No statistically significant change in flap thickness was detected in either group at any assessment time. There was a partial positive correlation (after controlling for preoperative manifest refractive spherical equivalent) between central flap thickness and preoperative ultrasound central pachymetry (r = 0.739, P = 0.036) in the MSU90 group but not in the MSU130 group. CONCLUSION: Using OCT, changes in flap thickness were minimal in the first month after LASIK. Flap thickness correlated strongly with central corneal thickness if a 90 µm head was used.
RESUMEN
PURPOSE: To evaluate the flap-producing characteristics of the VisuMax femtosecond laser system and their relationship to visual and refractive outcomes after laser in situ keratomileusis (LASIK). SETTING: Dr. Sulaiman Al Habib Medical Center, Dubai Healthcare City, Dubai, United Arab Emirates. DESIGN: Case series. METHODS: A review of LASIK cases from December 2008 to December 2009 was performed. Parameters recorded included the achieved flap thickness measured with intraoperative ultrasonic pachymetry, laser energy, side-cut angle, visual outcomes including uncorrected (UDVA) and corrected (CDVA) distance visual acuities and manifest refraction, higher-order aberrations using Hartman-Shack wavefront analysis, and complications. RESULTS: The study comprised 98 patients (195 eyes). The femtosecond laser energy for flap preparation was 160 to 200 nJ. The mean achieved flap thickness was 91.35 µm ± 12.26 (SD) (attempted 80 µm), 98.5 ± 14.39 µm (attempted 90 µm), 109.94 ± 13.43 µm (attempted 100 µm), 112.7 ± 7.45 µm (attempted 110 µm), and 123.82 ± 9.64 µm (attempted 120 µm). Postoperatively, 87% of eyes were within ± 0.25 diopter of the intended spherical equivalent, 75% had a UDVA of 20/16 (-0.1 logMAR) or better, and 42% gained 1 or more lines of visual acuity; no eye lost CDVA. No statistically significant relationships were found between energy, side-cut angle, achieved flap thickness, and refractive and visual outcomes. Complications were mild and did not affect final visual outcomes. CONCLUSION: The femtosecond laser yielded precise flap dimensions with a narrow standard deviation and a high level of safety. FINANCIAL DISCLOSURE: Neither author has a financial or proprietary interest in any material or method mentioned.