Refractive Lenticule Extraction

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Early results of newer lasers suggest competition for SMILE. Howard Larkin reports from the 39th Congress of the ESCRS in Amsterdam. Over the past decade, small incision lenticule extraction (SMILE) using the VisuMax® femtosecond laser (Carl Zeiss Meditec, Germany) has established itself as a viable alternative to LASIK and PRK for corneal refractive surgery. Now two more options are emerging in the refractive lenticule extraction market: corneal lenticule extraction for advanced refractive correction (CLEAR) using the FEMTO LDV Z8 and Z8 NEO femtosecond laser platforms (Ziemer), and SmartSight, using the ATOS femtosecond laser (SCHWIND eye-tech-solutions). Both are CE marked for the procedures. Maja Bohač MD, PhD presented the first European results of SmartSight at the Congress. LOWER LASER POWER Potential improvements the ATOS system brings include lower laser power levels at higher repetition rates, which may result in a more accurate treatment, and cyclotorsion control during surgery, which may improve astigmatism correction and decrease vertical coma, Dr Bohač said. The device also adds a refractive transition zone at the edge of the lenticule, possibly improving quality of vision. Because the lenticule has a zero-thickness edge, it is easier to extract without leaving lenticule fragments behind and requires no minimum lenticule thickness, she added. In a non-randomised prospective cases series enrolling 60 eyes of 31 patients, 97% achieved uncorrected distance visual acuity (UDVA) of 20/20 or better three months after surgery, Dr Bohač reported. All achieved a spherical equivalent (SEQ) refraction within 0.5 dioptres of the target, and UDVA postoperative was within 1 Snellen line of preoperative corrected vision for 97% of patients. She expects unaided vision will continue to improve. All patients underwent uneventful SmartSight lenticule extraction, Dr Bohač said. Preoperatively, mean spherical manifest refraction (MRSE) was -4.9±1.7 D (-3.25 to -7.5), and astigmatism was -0.62±0.33 D (-2.00 to -0.25). “An excellent refractive outcome was observed in terms of manifest refraction, but this was only partly confirmed by the objective refraction and topographical changes. This suggests manifest refraction may be more forgiving in [precisely] determining accuracy of the treatments. At the same time, UDVA is the main driver for patient satisfaction,” Dr Bohač said. Safety was also satisfactory. One eye lost two Snellen lines of CDVA, though this reversed after a few months, caused by severe dry eye and interface haze due to use of cyclosporine during recovery, Dr Bohač said. Higher-order aberrations were induced, but not at levels that rose to clinical significance, she added. The three-month results of this cohort have been submitted for publication. Samuel Arba-Mosquera PhD, of SCHWIND, reported similar 12-month results for SmartSight lenticule extraction from a study conducted by Kishore Raj Pradhan MD, Head of Refractive Surgery at the Tilganga Institute of Ophthalmology and Director of Matrika Eye Center, Kathmandu, Nepal. The observational study included 221 eyes of 114 patients consecutively treated with SmartSight. The mean age of patients was 28 years with a mean spherical equivalent manifest refraction of -6.26 D and astigmatism of 0.92 D before surgery. These values lowered to an SEQ of +0.48 D and astigmatism of 0.13 D one year after surgery. Mean postoperative uncorrected distance vision was 20/21, with 96% reaching 20/20. Most, 95%, had uncorrected postoperative vision within one line of best-corrected preoperative vision, Dr Arba-Mosquera reported. Just 1% of eyes lost one line, and no eyes lost two lines of corrected vision. In terms of objective refractive outcomes, R2 for attempted versus actual change in K readings for SEQ was 0.886. There was a trend towards less accuracy at higher corrections, with 70% of eyes within 1.0 D of the ideal average K for the intended target, Dr Arba-Mosquera said. Postoperative changes in central corneal thickness and central stromal thickness were minimal over the 12 months, suggesting about 3.0 μm of corneal (epithelial) remodelling, he noted. Correction of spherical error was more predictable than for astigmatism, but both were substantially improved. The three-month results of part of this cohort have been publishedi, and these 12-month reported results are accepted for publication. ANOTHER OPTION There were also reports of successful corneal lenticule extraction using the FEMTO LDV Z8, which also features lower pulse power and the ability to recentre the laser after docking. These studies include a series of five eyes where a complete lenticule dissection and extraction were performed through two 3.0 mm tunnel incisions, one leading to the posterior and one to the anterior planes. Clear corneas were observed on the first day post-surgery.ii Similarly, a prospective study involving 24 eyes in 24 patients operated with the FEMTO LDV Z8 for moderate to high myopia reported a median value of uncorrected visual acuity one week after surgery of decimal 0.9 (0.7–1.0), and after one month of 1.0 (1.0–1.0). The research did not observe any intra-or postoperative complications, and 79.2% of patients had no loss of maximum corrected visual acuity. The mean corneal thickness before surgery was 555.9±28.2 μm, which decreased significantly to an average value of 464.8±26.9 μm one week after surgery (p<0.05).iii i J Refract Surg., 2021 May; 37(5): 304–311. ii Izquierdo L et al., J Cataract Refract Surg., 2020 Sep; 46(9): 1217–1221. iii Doga AV et al., Vestn Oftalmol., 2020; 136(6. Vyp. 2): 214–218. Maja Bohač is Head of Refractive Surgery at the Svjetlost Eye Clinic, Zagreb, Croatia. maja.bohac@svjetlost.hr Samuel Arba-Mosquera PhD is an optical and vision researcher at SCHWIND eye-tech-solutions. samuel.arba.mosquera@eye-tech.net