A review of 800 cases of small incision lenticule extraction for treatment of myopia and myopic astigmatism shows an evolution in surgical indications and technique with consistently positive outcomes.
Reviewed by Jean-François Faure, MD
Small-incision lenticule extraction (SMILE) performed using a proprietary femtosecond laser (VisuMax, Carl Zeiss Meditec) to create an intrastromal lenticule deserves consideration as the new “gold standard” for surgical treatment of myopia and myopic astigmatism, according to Jean-François Faure, MD.
Dr. Faure, in private practice, Espace Nouvelle Vision Refractive Surgery Center, Paris, formed his opinion based on a review of his experience with SMILE in 800 eyes operated on over a period of 4 years.
“My technique has evolved over time, and I have expanded my indications so that I am performing SMILE for lower amounts of myopia and higher levels of astigmatism,” he said. “Considering the advantages of this flapless, minimally invasive technique and my successful outcomes, SMILE is now my preferred refractive surgery procedure for treating myopia and myopic astigmatism.”
Dr. Faure analyzed the surgical parameters and outcomes for his cohort of 800 SMILE eyes by dividing them into four groups of 200 eyes each that were operated on from March 2012 to September 2013, September 2013 to June 2014, June 2014 to December 2014, and December 2014 to October 2015.
All patients were selected for the procedure using classical refractive surgery eligibility criteria. Over the course of time, the maximum manifest refractive spherical equivalent (MRSE) treated stayed about the same (range, –9.5 to –10.0 D). However, the minimum MRSE was reduced from –1.5 D to –0.75 D and the maximum amount of cylinder treated increased from –1.5 to –3.5 D
Corresponding with the decrease in level of myopia treated, minimum lenticule thickness also decreased. However, there were no safety issues encountered with the need to extract thinner lenticules.
“The thinnest lenticule has been just 33 μm in eyes being treated for –0.75 D of myopia, but looking across the four surgical cohorts, there is no significant difference in terms of adverse events occurring secondary to difficulty with lenticule extraction,” Dr. Faure said.
Reduced incision size
Reviewing changes in his laser parameters over time, Dr. Faure noted he also reduced the size of the incision through which he performed lenticule extraction. In his initial group of 200 eyes, the mean incision size was 3.4 mm, but it averaged 2.21 mm in his most recent cohort.
“The femtosecond laser is used to make the incision for lenticule extraction, and the minimum size incision that can be created with the laser is 2 mm,” Dr. Faure explained.
Changes in cap depth also occurred over time. Initially, caps were created with a maximum depth of 140 μm and at a minimum depth of 105 μm. In his second and third cohorts of 200 eyes, Dr. Faure used a maximum cap depth of 160 μm, but he returned to the 140-μm depth most recently while the minimum cap depth increased progressively over time from 105 to 120 μm.
Dr. Faure has also modified his approach for lenticule dissection and extraction over time and he has now standardized the technique as follows. First, he uses a micromanipulator to lift the incision area and make sure he is on the anterior plane of the lenticule, and then he creates a tunnel in the posterior plane. To dissect the anterior lenticule, Dr. Faure follows a Y-shaped progression and dissects beyond the side cut. The attached triangle of tissue retained with this approach provides sufficient strength to enable further complete dissection of the anterior plane, he explained.
Using the same approach, Dr. Faure then dissects the posterior plane. For lenticule extraction, he now favors hydroexpulsion rather than removal with a microforceps.
Dr. Faure observed that the refractive and functional results have been consistently good across the four cohorts of eyes. Looking at the most recent 200 cases, 94% of eyes achieved 20/25 or better uncorrected distance visual acuity (UDVA) at 1 month after surgery, and the proportion increased to 97% at 6 months postoperatively. Mean MRSE in the same cohort was –0.08 D at 1 month and stable at –0.10 D at 6 months.
Adverse events have been minimal across the entire series. Among all four groups, residual epithelial cells in the interface requiring surgical removal affected between 0.5% and 1.5% of eyes. Only two eyes in the entire series required a surgical revision.
Jean-François Faure, MD
This article was adapted from Dr. Faure’s presentation at the American Society of Cataract and Refractive Surgery meeting. Dr. Faure has no relevant financial interest to disclose.