Wavefront excimer laser refractive surgery for adults with refractive errors

Authors: Li S-M, Kang M-T, Wang N-L, Abariga SA.

Geographical coverage: Asia, Europe, and the United States

Sector: Biomedical

Sub-sector: Treatment

Equity focus: None

Study population: Adults aged 18+.

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: Refractive errors, the most common cause of visual impairment, occur when the eye can’t accurately focus objects on the retina. Low-order aberrations like myopia, hyperopia, and astigmatism are typically corrected with glasses, contact lenses, or standard refractive surgery. Higher-order aberrations (HOAs) can be measured with wavefront aberration tools and corrected using wavefront-guided or wavefront-optimised laser surgery. Wavefront-guided procedures are based on pre-surgery HOA measurements, while wavefront-optimised procedures aim to minimise new HOAs and preserve existing ones. Both wavefront procedures are expected to yield better visual acuity than conventional methods.

Objectives: 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.

Main findings:

Overall, authors found at 12 and six months postoperatively, there was no important difference between wavefront versus conventional refractive surgery or between wavefront-optimised versus wavefront-guided surgery in the clinical outcomes analysed.

The study encompassed 33 Randomised Controlled Trials (RCTs) from Asia, Europe, and the United States, involving 1,499 participants (2,797 eyes). These participants had refractive errors varying from high myopia to low hyperopia. The studies reported at least one of the following outcomes: uncorrected visual acuity (UCVA) of 20/20 or better, no loss of one or more lines of best spectacle-corrected visual acuity (BSCVA), within ± 0.50 dioptres (D) of target refraction, presence of higher-order aberrations (HOAs), and adverse events. The majority of participants were women, aged between 29 and 53 years, with no history of refractive surgery, ocular pathology, or systemic comorbidity.

Authors note that risk of bias could not be judged for most domains of most studies. Most studies in which both eyes of a participant were analysed failed to account for correlations between two eyes in the analysis and reporting of outcomes.

The study compared wavefront (PRK, LASIK, LASEK) and conventional procedures, with 12-month outcome data available from only one PRK study. No significant benefits of wavefront PRK were found in terms of uncorrected visual acuity, best spectacle-corrected visual acuity, target refraction, and mean spherical equivalent. According to authors the evidence was of low certainty. At six months, results from multiple studies suggested no difference in all outcomes. Comparing wavefront-optimised and wavefront-guided procedures at 12 months, no significant differences were found in various outcomes, except for wavefront-optimised LASIK, which may improve mean spherical equivalent.

A single study comparing wavefront-guided LASIK and PRK at six and 12 months found no difference between the two procedures. Significant visual loss or optical side effects were similar across groups. The certainty of evidence was very low for all estimates.

Findings from this review indicate that wavefront ablations therapy in refractive surgery had no clear advantage over conventional ablation procedure in terms of traditional outcome measures among refractive surgery candidates who have higher-order aberrations (HOAs) in the normal range. The rationale for these procedures should be reconsidered. If wavefront ablation in refractive surgery is more expensive than conventional ablation, the additional cost is unjustified for most candidates, given the lack of evidence for their effectiveness over conventional procedures. For refractive surgery candidates with high pre-existing HOAs, wavefront ablations may be a worthwhile option. For those candidates with very high myopia (< -9.0 D) or moderate to high hyperopia (> +2.0 D), wavefront ablation refractive surgery should be considered carefully, because the trials included in the review did not enrol participants with refractive errors in those ranges.

The authors recommend re-evaluating refractive surgery approaches for individuals with high pre-existing Higher-Order Aberrations (HOAs). They question the reasonableness of the 0.3 μm threshold used in some studies to screen participants with high HOAs. They suggest considering the interaction among different HOA patterns for wavefront ablation refractive surgery and using more specific or task-related outcomes, such as reading or driving, for assessment. They propose that changes in HOAs might be better evaluated using lower contrast rather than the usual 100% contrast for visual acuity assessment. They call for larger Randomised Controlled Trials (RCTs) with longer follow-up periods to detect or rule out clinically meaningful differences over time, accounting for eye correlation in paired-eye designs. They also suggest including tear film outcomes in future research, as restoring a normal tear film and ocular surface may take a year or longer.

Methodology:

he authors included only Randomised Controlled Trials (RCTs) with participants aged 18 or older, who were randomly assigned to either wavefront or conventional excimer laser refractive surgery. Trials with a subgroup of participants under 18 were also included if over 75% of the study population were 18 or older, or if data for participants 18 years or older was reported separately.

A search for RCTs and controlled clinical trials was conducted on 6 August 2019, with no restrictions based on language or publication year. The databases searched included the Cochrane Central Register of Controlled Trials (CENTRAL), Medline Ovid, EMBASE Ovid, LILACS, the US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov, and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP).

Two authors independently evaluated full-text reports and classified each study. Data from each eligible study was independently extracted by two authors onto a web-based form in Covidence. Each included trial was independently assessed for risks of bias by two authors, according to the Cochrane Handbook for Systematic Reviews of Interventions.

Clinical and methodological heterogeneity was assessed among trials to determine whether meta-analysis was appropriate. When substantial clinical or methodological heterogeneity was found, the studies were not combined quantitatively, but a narrative summary of the trial results presented. Subgroup analyses were conducted to explore heterogeneity based on predetermined characteristics such as laser platform, ablation algorithm, and corneal flap creation method. A random-effects model was used for all analyses.

The authors had planned to restrict the analysis to high-quality and published studies, but this was not done as none of the included studies were at low risk of bias and no unpublished data was obtained. Sensitivity analyses were conducted to evaluate the impact of excluding studies with extreme intervention effect estimates or those conducted among participants with hyperopia, and the impact of excluding industry-funded studies.

A post hoc plan to restrict analysis to studies that analysed data at the participant level was not carried out due to an insufficient number of such studies.

Applicability/external validity: Authors indicate their findings are consistent with those of other reviews published to date.

Geographic focus: There is evidence of some studies produced in LMICs included in review. However, the authors do not consider how their findings might vary by geographic context.

Summary of quality assessment:

The approaches undertaken to identify, include and critically appraise studies were highly robust, with an unrestricted search (in terms of date, language and publication status) and with two authors undertaking all key tasks. The approach to the analysis of the data was also highly robust, with authors having detailed strategies in place to analyse the included studies and to check the validity of the results. Therefore, a high confidence in the findings of this review.