Myopic laser vision correction
Contralateral eye comparison measures SMILE against topography-guided LASIK.
A randomised, contralateral eye-controlled study of myopic correction with topography-guided femtosecond LASIK and small incision lenticule extraction (SMILE) showed the two procedures provided comparable refractive outcomes, despite better centration with LASIK.
LASIK was also associated with better visual performance, but SMILE resulted in less dry eye, inflammation and epithelial remodelling, according to A John Kanellopoulos MD.
Providing his conclusions, Dr Kanellopoulos highlighted the future promise of SMILE rather than its current limitations. “The results underline how effective laser vision correction is today, and the refractive outcomes for both procedures far exceeded the FDA standards,” said Dr Kanellopoulos, Director, LaserVision Clinical and Research Eye Institute, Athens, Greece.
“Considering that the SMILE cohort included cases done in my personal learning curve, the effectiveness of that procedure was outstanding, and I expect that potential future improvements in centration, tissue removal customisation and cyclorotation compensation may make SMILE-like procedures even superior to LASIK for correcting low-to-moderate myopia,” he added
The single-surgeon, rigorously designed study enrolled 25 patients undergoing bilateral eye treatments with -3.0D to -10.0D of myopia (mean -5.5D) and up to -5.0D of astigmatism (mean -1.5D).
Mean distance uncorrected visual acuity (UCVA) was 20/200 preoperatively for both groups, and at six months was 20/20 in SMILE eyes and 20/15 after LASIK. The efficacy analysis comparing postoperative UCVA with preoperative corrected distance visual acuity (CDVA) showed a one-line gain of CDVA vision for 52% of LASIK eyes and 30% of SMILE eyes.
Refractive results for both surgeries showed excellent predictability and good stability. The refractive outcomes were statistically better for the LASIK-treated eyes, however, and particularly for cylinder correction.
“It is inherent to the topography-guided treatment for it to be better, and a comparison between the two procedures is a little unfair considering there is currently no cyclorotation adjustment with SMILE,” said Dr Kanellopoulos, who is also Clinical Professor of Ophthalmology, New York University Medical School, New York, USA.
Additionally, topography-modified refraction (TMR: modification of the amount and axis of astigmatism according to the topography values and angle kappa) was used in the LASIK eyes, potentially enhancing the visual performance recorded.
Contrast sensitivity was improved postoperatively in both groups, although it was better after LASIK than SMILE.
Stating that he has advocated judging refractive surgery with assessments other than conventional visual performance and keratometry measures, Dr Kanellopoulos said that the study endpoints also included analyses of corneal symmetry indices and ablation centration.
He reported that the index of height decentration (IHD) was lower at one, three and six months in the LASIK eyes compared with SMILE, although the difference between groups tended to dissipate as follow-up lengthened.
“Lower IHD means better regularity of the cornea, and the difference favouring LASIK is probably due to its better accuracy for correcting corneal astigmatism in regard to the corneal vertex (line of sight),” Dr Kanellopoulos said.
“We also looked at the Objective Scatter Index as a marker of quality of vision and found the results were better after LASIK, which probably is because of better corneal symmetry,” he added.
Centration was assessed by digital analysis of Scheimpflug sagittal curvature maps to calculate the difference between the achieved (centre of corneal curvature flattening effect on the anterior curvature sagittal map difference between pre- and post-op) and planned centre of the lenticule or ablation (the corneal vertex). The results showed far better centration for LASIK than SMILE (mean decentration of 150μm versus 450μm respectively) and highlighted that centration is still an issue with SMILE, Dr Kanellopoulos noted.
Measurements of epithelial remodelling showed significant changes in the SMILE eyes, more than anticipated. Nevertheless, less remodelling epithelial effect in SMILE eyes and faster recovery as the epithelial changes, appeared to significantly subside by month 3. Central and mid-peripheral epithelial thickness increased significantly after both procedures, but the changes were more significant in the LASIK eyes.
“Still, SMILE does not seem to leave the ocular surface minimally affected. It is speculated that there is less denervation after SMILE since the side cut transversing the subepithelial nerve plexus of the cornea is just 50 degrees, compared to 310 degrees in LASIK. Our findings argue with this theory and potentially support that corneal epithelial remodelling is more curvature change-related, and not just transient dry eye-related,” said Dr Kanellopoulos.
Some minor complaints of dry eye symptoms were more common after LASIK than SMILE and persisted longer. At six months, dry eye symptoms had significantly subsided in both groups and were reported for the SMILE eye by six patients (24%) and for the LASIK eye by 12 patients (48%).
A John Kanellopoulos: firstname.lastname@example.org