The technique differs from standard LASIK procedures in that it has eliminated the ablation segment of the procedure. Instead, a small lenticule is cut in the stroma and removed from the eye through a small incision. The challenges faced when learning this technique include centration, suction loss, difficult dissection, and the lenticule being stuck to the cap.
Dr. Ibrahim, professor of ophthalmology and president, Alexandria University, Egypt, has performed this flapless procedure on about 600 eyes. The mean patient age was 28 years (range, 16 to 64 years). The mean preoperative manifest refractive spherical equivalent (MRSE) was –6.67 ± 3.16 D (range, –1.25 to –17 D); the mean sphere was –6.05 ± 3.14 D (range, –0.25 to –16 D); and the mean cylinder was –1.23 ± 1.02 D (range, up to –6 D).
One week after surgery, in 534 eyes the mean postoperative spherical equivalent was 0.23 ± 0.63 D (range, +1.75 to –3 D). The mean sphere was 0.13 ± 0.59 D (range, +1.75 to –2.75 D). The mean cylinder was 0.21 ± 0.47 D (range, up to –2 D). One month postoperatively, the respective values were 0.16 ± 0.51 D (range, +1.50 to –2.25 D), 0.09 ± 0.47 D (range, +2 to –2 D), and 0.14 ± 0.41 D (range, up to –1.75 D).
By the 1-year time point, about 300 eyes were evaluated. The mean spherical equivalent was –0.17 ± 0.48 D (+1 to –3 D), the mean sphere was 0.08 to 0.43 (range, +1.50 to –3 D), and the mean cylinder was –0.18 ± 0.45 D (range, up to –2.25 D), Dr. Ibrahim said.
About 88% of cases were within ±0.5 D of the intended correction. When cases were analyzed by the degree of myopia, the results were similar across low, intermediate, and high myopia.
"The procedure was found to be extremely stable over time," Dr. Ibrahim said. "With follow- up to 1 year, there was almost no change in MRSE over time. This indicated that there was no marked effect of the wound healing."
This same result was seen when the subgroups of myopia were evaluated and indicated that this is the procedure of choice for patients with high myopia.
Regarding predictability, most cases were very near the intended correction with some tendency for undercorrection.
During the early follow-up period, some patients lost lines of corrected distance visual acuity, but this loss was temporary and improved over time.
"In addition, many patients gained lines of visual acuity over time," Dr. Ibrahim said.
The procedure induced minimal astigmatism. At the 1-year examination, about 90% of patients had less than 1 D of astigmatism.
"Compared [with] the conventional LASIK procedure, [this flapless procedure] has better corneal biomechanics and stable correction," he said. "It induces much less dry eye [because] it has no flap cutting.
"It is ideal for treating [patients with high myopia] because the same time is required to correct different refractive errors," he added. "Minimal astigmatism was induced. Less higher-order aberrations are induced. Tissue removal is much better than tissue ablation."
The challenges that need to be faced are re-sidual error, which can be corrected with PRK or a re-cut. The procedure must be customized with wavefront-guided procedures. Study of the corneal biomechanics should show that cutting the tissue preserves the biomechanics. Finally, the correction of hyperopia should be addressed, Dr. Ibrahim concluded.
Dr. Ibrahim is a consultant to Carl Zeiss Meditec.