How to create viable thin-flap layers in LASIK

Take-Home

Study of fourier OCT to evaluate flap architectures in LASIK patients finds that both a mechanical microkeratome and a femtosecond laser create thin planar flaps.

Dr. Perez-Straziota

By Cheryl Guttman Krader; Reviewed by Claudia Perez-Straziota, MD

Gainesville, GA-Results of a retrospective study evaluating patients who underwent myopic LASIK show that both a mechanical microkeratome and a femtosecond laser can be used to create thin, planar flaps and are associated with excellent clinical outcomes.

“Thin, planar flaps are important in LASIK to maintain corneal biomechanical integrity,” said Claudia Perez-Straziota, MD. “While there are pros and cons for using either a femtosecond laser or a mechanical microkeratome for flap creation, our study shows that both technologies can be a reliable option for creating flaps with the desired morphology.

“However, this conclusion applies only to the devices evaluated in our study,” continued Dr. Perez-Straziota, private practice in Gainesville, GA. “It is unwise to assume that all femtosecond lasers and all microkeratomes create flaps with equivalent morphology.”

Reviewing the study

The analyses included data from 145 eyes of 73 patients operated on by a single surgeon (J. Bradley Randleman, MD, professor of ophthalmology at Emory Eye Center, Atlanta, GA).

In 91 eyes, the Femto LDV femtosecond laser (Ziemer Ophthalmic Systems) was used to create flaps with an intended thickness of 110 μm.

Fifty-four eyes had flap creation using the Amadeus II mechanical microkeratome (Ziemer Ophthalmic Systems) using a 9-mm or 9.5-mm suction ring, the 140-μm head, and ML7090CLB blades (Med-Logics).

Expected flap thickness was 105 μm, and all patients underwent a wavefront-optimized ablation with a single excimer laser platform (Allegretto Wave, Alcon).

There were no significant differences between groups preoperatively in mean patient age, uncorrected distance VA (UCVA), mean MRSE, or mean central corneal thickness. All eyes also had best corrected distance visual acuity (CDVA) of 20/20 or better.

Central flap thickness was calculated intraoperatively by subtraction based on ultrasound pachymetry measurements of preoperative central corneal thickness (CCT) and intraoperative residual stromal bed thickness.

Analyzing the results

The results showed mean flap thickness with both techniques was close to the intended, but the microkeratome flaps were significantly thinner than the femtosecond laser flaps (106 vs. 113 microns).

Flap morphology was assessed at 2 weeks postoperatively using anterior segment Fourier domain OCT (RTVue, Optovue) to measure thickness at 9 points across the central 3 mm of the cornea (horizontal and vertical meridians at 1.5 mm and 2.5 mm, and corneal apex).

For the femtosecond laser flaps, vertical meridian measurements ranged between 125 μm and 135 μm, and horizontal meridian measurements ranged from 125 μm to 132 μm.

For the microkeratome flaps, vertical meridian measurements ranged from 112 μm to 117 μm, and horizontal meridian measurements were 111 μm to 117 μm.

“These data show planar flaps were created using either technology,” Dr. Perez-Straziota said. “The microkeratome flaps had lower and less variable standard deviation in all points measured . . . (but) microkeratome still remains a viable option for creating thin, planar flaps.

“However, the femtosecond laser offers some advantages as the potential complications from flap creation with the laser are certainly less devastating, and the patient preference is undeniable,” she continued.

Clinical outcomes were evaluated at 1 day, 2 weeks, and 3 months postoperatively, and included uncorrected and best-corrected distance visual acuity (UDVA and CDVA) and MRSE.

There were no significant differences between the two study groups in any of these measures at any of the follow-up visits, and the results were excellent in both groups, Dr. Perez-Straziota said.

On the first day after surgery, average UCVA was 20/21 in the microkeratome eyes and 20/23 in the femtosecond laser group. At 3 months, average UDVA was 20/19 in the microkeratome eyes and 20/21 in the femtosecond laser group. Average MRSE was plano in both groups. Average CDVA was 20/18 in both groups at all follow-ups.

Claudia Perez-Straziota, MD

E: straziotamd@gmail.com

Dr. Perez-Straziota does not have any relevant financial interests to disclose.

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