Inverted side cut has potential benefits in LASIK

Take-Home

Use of an inverted side cut when performing LASIK speeds recovery of corneal sensation.

Dr. Manche

By Lynda Charters; Reviewed by Edward E.Manche, MD

Palo Alto, CA-Corneal sensation recovered significantly faster in patients who underwent femtosecond LASIK flap creation in which an inverted side cut was made compared with a conventional side cut.

However, no relevant clinical differences in self-reported symptoms, such as pain, dry eye, foreign body sensation, or light sensitivity, were seen between the two groups.

Edward E. Manche, MD, and colleagues conducted a prospective, randomized contralateral study that included 61 patients (122 eyes). Previous research promoted them to investigate the potential benefits of the inverted side cut.

Michael Knorz MD, and Urs Vossmerbaeumer (J Refract Surg. 2008:24:875-878) found increased flap adhesion postoperatively for optimal wound healing and three times greater flap stability compared with microkeratome-created flaps. A second study by Eric Donnenfeld, MD (Invest Ophthalmol Vis Sci. 2010;51:E-Abstract 2855) found improved severed nerve apposition with the inverted side cut.

“These results could potentially improve the dry eye findings,” said Dr. Manche, director, Cornea and Refractive Surgery, Stanford Eye Laser Center, and professor of ophthalmology, Stanford University School of Medicine, Palo Alto, CA.

All patients had undergone bilateral simultaneous LASIK during which flaps were created using the 150-kHz femtosecond laser (Intralase iFS, Abbott Medical Optis [AMO]) in one eye and another femtosecond laser (Intralase FS 60, AMO) in the fellow eye; the former created an inverted side cut and the latter created a standard bevel cut.

The excimer laser (CustomVue S4, AMO) was used to perform the ablation. Corneal sensation was measured preoperatively and then at 1,3, 6, and 12 months postoperatively using the Cochet-Bonnet aesthesiometer (Luneau). Patients completed a questionnaire on dry eye symptoms at the same time points, according to Dr. Manche.

The two groups were well matched preoperatively, with no significant differences in both lower and higher-order aberrations.

The two lasers were both programmed for a 105-mm flap thickness with a 9-mm superior hinge. For the eyes treated with the iFS 150 laser, a 130° inverted side cut was used with a 150-kHz repetition rate; with the FS 60 laser, a 70° beveled cut was used with a 60-kHz repetition rate, Dr. Manche explained.

The results showed the expected corneal denervation 1 month postoperatively in both groups. The differences between the two groups did not reach significance at one month.

“At 3, 6, and 12 months postoperatively, there was a significantly (p < 0.01, for all comparisons) greater recovery of central corneal sensation in the eyes with the inverted side cut compared with the eyes with the beveled cut,” Dr. Manche said.

The flap thicknesses created by both lasers were not a confounding variable because the thicknesses were the same over the central 6 mm of the cornea as measured with anterior segment ocular coherence tomography, he noted.

Survey findings

The patient questionnaire evaluated dryness according to frequency, severity, and degree of being bothersome.

“Initially, during months 1 and 3 postoperatively the patients all had increases in these factors,” Dr. Manche said. “At 6 and 12 months the symptoms decreased to below the preoperative levels with both lasers. There were no significant differences between the laser platforms.”

Foreign body sensation followed the same trends for frequency, severity, and bothersomeness as dryness, with an initial increase and a later decrease at 3, 6, and 12 months to below the preoperative levels. Again, there were no significant differences between the lasers.

The same nonsignificant trends were seen for pain or discomfort with both lasers.

“Interestingly, the patients reported less pain at all intervals after the surgery than preoperatively,” Dr. Manche said.

Patients reported that the increased light sensitivity postoperatively resolved by 6 and 12 months postoperatively with both lasers with no significant differences.

“We found a significantly greater reduction in corneal sensation in the eyes in which a conventional side cut was made compared with those in which an inverted side cut was made, faster recovery of corneal sensation in the inverted side cut eyes compared with the conventional side cut eyes, and no difference between the groups in self-reported dry eye symptoms, foreign body sensation, pain, and light sensitivity,” Dr. Manche summarized.

Edward E.Manche, MD

E: eemanche@yahoo.com

Abbot Medical Optics provided an unrestricted grant to partially fund this study.