Comparison of visual outcomes after variable spot scanning ablation versus wavefront-optimized myopic LASIK

Comparison of Changes in Corneal Thickness and Curvature After Myopia Correction Between SMILE and FS-LASIK

PURPOSE

To comparatively investigate the changes in corneal thickness and curvature between small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK).

METHODS

Data were collected preoperatively and postoperatively at 1 week, 1 month, and 3 months, including central corneal thickness (CCT), midperipheral corneal thickness (MPCT), peripheral corneal thickness (PCT), central keratometry (CK), midperipheral keratometry (MPK), and peripheral keratometry (PK), using a dual rotating Scheimpflug analyzer.

RESULTS

At 1 week postoperatively, changes in CCT, MPCT, PCT, and PK were significantly greater in the SMILE group than in the FS-LASIK group (P = .003 for CCT and < .001 for MPCT, PCT, and PK), but no significant inter-group differences were found between changes in CK and MPK (P = .883 and .513, respectively). CCT, MPCT, and PK values showed a similar increase in both groups, but significantly more increase in PCT and significantly less increase in CK and MPK was observed in the SMILE group from 1 week to 3 months after surgery. At 3 months postoperatively, CCT and MPCT were significantly thinner in the SMILE group than in the FSLASIK group (P = .018 and .022, respectively), and there was no significant difference in PCT, CK, MPK, and PK between the two groups.

CONCLUSIONS

SMILE caused significantly more corneal thinning at the center, midperiphery, and periphery, and more corneal flattening at the periphery, compared to FS-LASIK. A different pattern of corneal remodeling was observed between the two surgeries during the 3-month follow-up period. [J Refract Surg. 2023;39(1):15-22.].

Wavefront excimer laser refractive surgery for adults with refractive errors

BACKGROUND

Refractive errors (conditions in which the eye fails to focus objects accurately on the retina due to defects in the refractive system), are the most common cause of visual impairment. Myopia, hyperopia, and astigmatism are low-order aberrations, usually corrected with spectacles, contact lenses, or conventional refractive surgery. Higher-order aberrations (HOAs) can be quantified with wavefront aberration instruments and corrected using wavefront-guided or wavefront-optimized laser surgery. Wavefront-guided ablations are based on preoperative measurements of HOAs; wavefront-optimized ablations are designed to minimize induction of new HOAs while preserving naturally occurring aberrations. Two wavefront procedures are expected to produce better visual acuity than conventional procedures.

OBJECTIVES

The primary objective was to compare effectiveness and safety of wavefront procedures, laser-assisted in-situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) or laser epithelial keratomileusis (LASEK) versus corresponding conventional procedures, for correcting refractive errors in adults for postoperative uncorrected visual acuity, residual refractive errors, and residual HOAs. The secondary objective was to compare two wavefront procedures.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, which contains the Cochrane Eyes and Vision Trials Register; 2019, Issue 8); Ovid MEDLINE; Ovid Embase; Latin American and Caribbean Health Sciences (LILACS); the ISRCTN registry; ClinicalTrials.gov and the WHO ICTRP. The date of the search was 6 August 2019. We imposed no restrictions by language or year of publication. We used the Science Citation Index (September 2013) and searched the reference lists of included trials to identify additional relevant trials.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) comparing either wavefront modified with conventional refractive surgery or wavefront-optimized with wavefront-guided refractive surgery in participants aged ⪰ 18 years with refractive errors.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodology.

MAIN RESULTS

We identified 33 RCTs conducted in Asia, Europe and United States, totaling 1499 participants (2797 eyes). Participants had refractive errors ranging from high myopia to low hyperopia. Studies reported at least one of the following review-specific outcomes based on proportions of eyes: with uncorrected visual acuity (UCVA) of 20/20 or better, without loss of one or more lines of best spectacle-corrected visual acuity (BSCVA), within ± 0.50 diopters (D) of target refraction, with HOAs and adverse events. Study characteristics and risk of bias Participants were mostly women, mean age 29 and 53 years, and without previous refractive surgery, ocular pathology or systemic comorbidity. We could not judge risks of bias for most domains of most studies. Most studies in which both eyes of a participant were analyzed failed to account for correlations between two eyes in the analysis and reporting of outcomes. Findings For the primary comparison between wavefront (PRK or LASIK or LASEK) and corresponding conventional procedures, 12-month outcome data were available from only one study of PRK with 70 participants. No evidence of more favorable outcomes of wavefront PRK on proportion of eyes: with UCVA of 20/20 or better (risk ratio [RR] 1.03, 95% confidence interval (CI) 0.86 to 1.24); without loss of one or more lines of BSCVA (RR 0.94, 95% CI 0.81 to 1.09); within ± 0.5 D of target refraction (RR 1.03, 95% CI 0.86 to 1.24); and mean spherical equivalent (mean difference [MD] 0.04, 95% CI -0.11 to 0.18). The evidence for each effect estimate was of low certainty. No study reported HOAs at 12 months. At six months, the findings of two to eight studies showed that overall effect estimates and estimates by subgroup of PRK or LASIK or LASEK were consistent with those for PRK at 12 month, and suggest no difference in all outcomes. The certainty of evidence for each outcome was low. For the comparison between wavefront-optimized and wavefront-guided procedures at 12 months, the overall effect estimates for proportion of eyes: with UCVA of 20/20 or better (RR 1.00, 95% CI 0.99 to 1.02; 5 studies, 618 participants); without loss of one or more lines of BSCVA (RR 0.99, 95% CI 0.96 to 1.02; I2 = 0%; 5 studies, 622 participants); within ± 0.5 diopters of target refraction (RR 1.02, 95% CI 0.95 to 1.09; I2 = 33%; 4 studies, 480 participants) and mean HOAs (MD 0.03, 95% CI -0.01 to 0.07; I2 = 41%; 5 studies, 622 participants) showed no evidence of a difference between the two groups. Owing to substantial heterogeneity, we did not calculate an overall effect estimate for mean spherical equivalent at 12 months, but point estimates consistently suggested no difference between wavefront-optimized PRK versus wavefront-guided PRK. However, wavefront-optimized LASIK compared with wavefront-guided LASIK may improve mean spherical equivalent (MD -0.14 D, 95% CI -0.19 to -0.09; 4 studies, 472 participants). All effect estimates were of low certainty of evidence. At six months, the results were consistent with those at 12 months based on two to six studies. The findings suggest no difference between two wavefront procedures for any of the outcomes assessed, except for the subgroup of wavefront-optimized LASIK which showed probable improvement in mean spherical equivalent (MD -0.12 D, 95% CI -0.19 to -0.05; I2 = 0%; 3 studies, 280 participants; low certainty of evidence) relative to wavefront-guided LASIK. We found a single study comparing wavefront-guided LASIK versus wavefront-guided PRK at six and 12 months. At both time points, effect estimates consistently supported no difference between two procedures. The certain of evidence was very low for all estimates. Adverse events Significant visual loss or optical side effects that were reported were similar between groups.

AUTHORS' CONCLUSIONS

This review suggests that at 12 months and six months postoperatively, there was no important difference between wavefront versus conventional refractive surgery or between wavefront-optimized versus wavefront-guided surgery in the clinical outcomes analyzed. The low certainty of the cumulative evidence reported to date suggests that further randomized comparisons of these surgical approaches would provide more precise estimates of effects but are unlikely to modify our conclusions. Future trials may elect to focus on participant-reported outcomes such as satisfaction with vision before and after surgery and effects of remaining visual aberrations, in addition to contrast sensitivity and clinical outcomes analyzed in this review.

Study of change in contrast sensitivity in relation to depth of ablation after wavefront optimized myopic laser-assisted in situ keratomileusis

Purpose:

The aim of this work was to study the change in contrast sensitivity (CS) in relation to depth of stromal ablation after wavefront-optimized (WFO) myopic laser in situ keratomileusis (LASIK).

Methods:

This was as prospective, longitudinal, comparative study. The study participants were divided into two groups: Group 1 ≤50 μ ablation depth; 60 eyes and group 2 >50 μ ablation depth; 60 eyes. All underwent WFO LASIK. Uncorrected and corrected distance visual acuity (UDVA and CDVA) and CS were measured preoperatively and postoperatively at 1 week, 2 weeks, and 2 and 6 months. Two-way repeated-measures analysis of variance (ANOVA), Unpaired t test and one-way repeated measures ANOVA were used to test differences across time periods within each treatment group. A value of P < 0.05 was considered as statistically significant.

Results:

The mean ablation depths in groups 1 and 2 were 39.30 μ ± 7.22 μ and 69.90 μ ± 12.09 μ, respectively; the maximum depth was 94.62 μ. In group 1, the preoperative mean CS was 1.91 ± 0.07, which improved postoperatively at 1 week (1.93 ± 0.06) and remained stable in subsequent follow-ups (1.94 ± 0.05). In group 2, the mean CS preoperatively was 1.87 ± 0.12, which postoperatively at 1 week and 6 months were 1.93 ± 0.07 and 1.94 ± 0.03, respectively (P < 0.05). Between the groups, preoperative CS was significantly different (P = 0.04), but the change in CS post-LASIK was insignificant (P > 0.05).

Conclusion:

There was a significant improvement in CS after WFO myopic LASIK in all patients irrespective of ablation depth (up to 94.62 μ).

Clinical Evaluation of LASEK for High Myopia Correction between the Triple-A Profile and the Zyoptix Tissue Saving Profile

Purpose

To compare the effects of correcting high myopia using the MEL®90 Triple-A profile LASEK at a 500 Hz pulse rate (Triple-A group) versus the Zyoptix tissue-saving ablations of Technolas 217z laser platform at 100 Hz (TS group).

Methods

This retrospective study included 50 eyes in the Triple-A group and 42 eyes in the TS group with manifest refraction spherical equivalent (MRSE) of -6 diopters (D) to -10 D. We compared uncorrected distance visual acuity, MRSE, corrected distance visual acuity, and postoperative complications at 1 month, 3 months, and 6 months.

Results

At 6 months after refractive surgery, the efficacy index of Triple-A group was significantly higher than that of the TS group (1.03 ± 0.12 vs 1.00 ± 0.11, P=0.04). The MRSE postoperatively in the Triple-A group was significantly lower than that in the TS group (0.25 ± 0.18 vs 0.38 ± 0.23, P < 0.01). The safety indices in the two groups were almost the same after 6 months of surgery (1.03 ± 0.07 vs 1.04 ± 0.11, P=0.63). The proportion of eyes which achieved ±0.13 D was significantly higher in the Triple-A group than that in the TS group at 1 month (80% vs 59.5%, P=0.03), 3 months (82% vs 61.9%, P=0.03) and 6 months (84% vs 64.3%, P=0.03). The changes in refraction 6 months after surgery comparing with 1 month after surgery were 0.12 ± 0.10 D in the Triple-A group and 0.13 ± 0.08 D in the TS group (P=0.56). All (100%) of the patients in the Triple-A group and 50% of the patients in the TS group had a UDVA of 20/16 at 6 months after surgery (P < 0.01). The induced spherical aberrations and total HOAs in the Triple-A group were significantly lower than those in the TS group (0.17 ± 0.02 μm vs 0.23 ± 0.02 μm, P < 0.01; 0.20 ± 0.04 μm vs 0.39 ± 0.03 μm, P < 0.01) at 6 months after surgery. The mean reduced corneal thickness was 113.06 ± 10.5 μm in the Triple-A profile group and 121.43 ± 23.46 μm in the TS group (P=0.02). No patient in either group had haze and high intraocular pressure 6 months after surgery.

Conclusion

For treatment of high-myopia patients, the Triple-A profile was more effective, predictable, and accurate than the Zyoptix tissue-saving profile. Meanwhile, the Triple-A profile had less induced spherical aberrations, total HOAs, and cornea ablation depth than the Zyoptix tissue-saving profile. Patients in the Triple-A group with 500 Hz pulse rate treatment achieved superior results. The two surgical procedures were equivalent in terms of safety and stability.

Excimer Lasers in Refractive Surgery

Introduction

In the field of ophthalmology, laser technology is used in many basic and clinical disciplines and specialities. It has played an important role in promoting the development of ophthalmology.

Aim

This article is designed to review the evolution of laser technology in refractive surgeries in ophthalmology, mainly focusing on the characteristics of the excimer laser applied in corneal refractive surgery.

Methods

This article was performed based on a literature review and Internet search through scientific databases such as PubMed, Scopus, Web of Science and Google Scholar.

Result

The literature on excimer laser technology addresses the technical and physical aspects of excimer lasers including types, characteristics and commercially available lasers on the market.

Conclusion

The conclusion on this forum aims to help understand the benefits of excimer laser use in ophthalmology, with focus on correction of refractive errors.

The Corneal Basement Membranes and Stromal Fibrosis

Purpose

The purpose of this review was to provide detailed insights into the pathophysiology of myofibroblast-mediated fibrosis (scarring or late haze) after corneal injury, surgery, or infection.

Method

Literature review.

Results

The epithelium and epithelial basement membrane (EBM) and/or endothelium and Descemet's basement membrane (BM) are commonly disrupted after corneal injuries, surgeries, and infections. Regeneration of these critical regulatory structures relies on the coordinated production of BM components, including laminins, nidogens, perlecan, and collagen type IV by epithelial, endothelial, and keratocyte cells. Whether a cornea, or an area in the cornea, heals with transparency or fibrosis may be determined by whether there is injury to one or both corneal basement membranes (EBM and/or Descemet's BM) and delayed or defective regeneration or replacement of the BM. These opaque myofibroblasts, and the disordered extracellular matrix these cells produce, persist in the stroma until the EBM and/or Descemet's BM is regenerated or replaced.

Conclusions

Corneal stromal fibrosis (also termed "stromal scarring" or "late haze") occurs as a consequence of BM injury and defective regeneration in both the anterior (EBM) and posterior (Descemet's BM) cornea. The resolution of fibrosis and return of stromal transparency depends on reestablished BM structure and function. It is hypothesized that defective regeneration of the EBM or Descemet's BM allows key profibrotic growth factors, including transforming growth factor beta-1 (TGF-β1) and TGF-β2, to penetrate the stroma at sustained levels necessary to drive the development and maintenance of mature opacity-producing myofibroblasts from myofibroblast precursors cells, and studies suggest that perlecan and collagen type IV are the critical components in EBM and Descemet's BM that bind TGF-β1, TGF-β2, platelet-derived growth factor, and possibly other growth factors, and regulate their bioavailability and function during homeostasis and corneal wound healing.

Comparison of efficacy, safety, and predictability of laser in situ keratomileusis using two laser suites

Purpose

The main aim of this study was to compare the efficacy, safety, and predictability of femtosecond laser-assisted in situ keratomileusis performed by two different laser suites in the treatment of myopia for up to 6 months.

Methods

In this two-site retrospective nonrandomized study, myopic eyes that underwent laser-assisted in situ keratomileusis using IntraLase FS 60 kHz formed group 1 and those using WaveLight FS200 femtosecond laser system formed group 2. Ablation was performed with Visx Star S4 IR and WaveLight EX500 Excimer lasers, respectively, in groups 1 and 2. Both groups were well matched for age, sex, and mean level of preoperative refractive spherical equivalent (MRSE). Uncorrected distance visual acuity, corrected distance visual acuity, and MRSE were evaluated preoperatively and at 1 week, 1 month, and 6 months after treatment.

Results

Fifty-six eyes of 28 patients were included in the study. At 6-month follow-up postop, 78.6% of eyes in group 1 and 92.8% of eyes in group 2 achieved an uncorrected distance visual acuity of 20/20 or better (P=0.252). 35.7% and 50% in group 1 and group 2, respectively, gained one line (P=0.179). No eye lost lines of corrected distance visual acuity. Twenty-five eyes in group 1 (92.7%) and 27 eyes in group 2 (96.3%) had MRSE within ±0.5 D in the 6-month follow-up (P>0.999). The mean efficacy index at 6 months was similar in group 1 and group 2 (mean 1.10±0.12 [standard deviation] vs 1.10±0.1) (P=0.799). The mean safety index was similar in group 1 and group 2 (mean 1.10±0.10 [standard deviation] vs 1.10±0.09) (P=0.407). Conclusion: The outcomes were excellent between the two laser suites. There were no significant differences at 6-month follow-up postop between the two laser systems.