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Authors; Rob Edge, and Jennifer Horton.
Unsatisfactory visual acuity as a result of uncorrected refractive errors is the single largest contributor to the global burden of vision conditions and has an adverse impact on the QoL of individuals around the world who are affected by it.1,2 The vast majority of refractive errors are addressed in the developed world, including Canada. Conventional vision technologies, such as eyeglasses and contact lenses, are a readily available, simple, and safe means of refractive error correction.
A variety of vision conditions are caused by refractive error and are candidates for correction with laser surgical interventions. Refractive error is a result of anatomic imperfection in the shape of the eyeball or 1 or more of its constituent parts. The cornea is on the outer surface of the eyeball. Precise reshaping of this transparent structure can correct refraction errors caused by a variety of anatomic imperfections. Vision conditions, such as myopia (nearsightedness), hyperopia (farsightedness), and astigmatism (uneven focus), can be corrected by different approaches using a laser to reshape the cornea to compensate for the different anatomic imperfections that incorrectly refract and focus light on the retina. Presbyopia is commonly the result of an age-related hardening of the lens of the eyeball and a decreasing ability to dynamically change the shape of the lens to optimize near visual acuity. More sophisticated laser surgical strategies can be applied to offer monovision to people with presbyopia through corneal reshaping, effectively creating a different focus in each eye or in different fields of view: 1 optimized for distance visual acuity and 1 optimized for near visual acuity.3,4 This results in a sacrifice in uncorrected distance stereoacuity.5 Keratoconus, another common eye condition resulting in refractive error, is a degenerative asymmetric thinning and deformation of the cornea resulting in astigmatism.6 A role for refractive laser surgery for people with keratoconus is less well established.7 Its relevance to refractive laser surgeries is more often cited as a contraindication due to the thinning cornea.8 For some very common vision conditions, refractive laser surgery has the potential to offer people an increased QoL by eliminating reliance on conventional vision technologies.
Refractive laser surgeries use an excimer laser, which was approved in Canada for PRK in 1991. Subsequently, LASIK has become the most commonly performed procedure.9 PRK and LASIK use a different surgical approach to access corneal tissue before reshaping it with the excimer laser. Additional variations on these procedures include Epi-LASIK and laser epithelial keratomileusis (LASEK).5
Conventional vision technologies, including contact lenses and eyeglasses, can eliminate refractive error with a very familiar and minimal risk profile and QoL impact. Evidence regarding the comparative clinical effectiveness, associated risk, and QoL benefits of refractive laser surgeries is required for both patients and health care decision-makers. The objective of this report was to retrieve and review the evidence regarding the clinical effectiveness of refractive laser surgery for people with vision conditions and to also retrieve and review evidence-based guidelines regarding the use of refractive laser surgery for this population.
An information specialist conducted a literature search on key resources, including MEDLINE, the Cochrane Database of Systematic Reviews, the International Health Technology Assessment (HTA) Database, the websites of Canadian and major international health technology agencies, as well as a focused internet search. The search approach was customized to retrieve a limited set of results, balancing comprehensiveness with relevancy. The search strategy comprised both controlled vocabulary, such as the National Library of Medicine’s MeSH (Medical Subject Headings), and keywords. Search concepts were developed based on the elements of the research questions and selection criteria. The main search concepts were refractive laser surgery and visual acuity. CADTH-developed search filters were applied to limit retrieval to health technology assessments, systematic reviews (SRs), meta-analyses (MAs), or indirect treatment comparisons; randomized controlled trials (RCTs), controlled clinical trials, or any other type of clinical trial; and guidelines. The search was completed on September 1, 2023, and limited to English-language documents published since January 1, 2018.
One reviewer screened citations and selected studies. In the first level of screening, titles and abstracts were reviewed and potentially relevant articles were retrieved and assessed for inclusion. The final selection of full-text articles was based on the inclusion criteria presented in Table 1.
Selection Criteria.
Articles were excluded if they did not meet the selection criteria outlined in Table 1 or were published before 2018.
The included publications were critically appraised by 1 reviewer using the following tools as a guide: A Measurement Tool to Assess Systematic Reviews 2 (AMSTAR 2)10 for SRs, and the Appraisal tool for Cross-Sectional Studies (AXIS) for cross-sectional studies.11 Summary scores were not calculated for the included studies; rather, the strengths and limitations of each included publication were described narratively.
A total of 276 citations were identified in the literature search. Following screening of titles and abstracts, 273 citations were excluded, and 3 potentially relevant reports from the electronic search were retrieved for full-text review. From the grey literature search, 1 potentially relevant report was retrieved for full-text review. Of these potentially relevant articles, 1 set of guidelines were excluded for lack of sufficient evidence-based development methods and 3 publications met the inclusion criteria and were included in this report. These comprised 1 SR and 2 nonrandomized studies. Appendix 1 presents the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)12 flow chart of the study selection.
The identified guidelines may be of interest, despite unreported methodology and ungraded recommendations. This reference is provided in Appendix 5.
Additional details regarding the characteristics of included publications are provided in Appendix 2.
The SR included in this report by Wu et al.13 was published in 2020. It included all 19 relevant RCTs on LASIK in the US FDA’s database that were published between 2003 and 2019 as well as 2 previously published Australian population studies. One study counted all new cases of contact lens–related microbial keratitis in Australia through surveillance of all ophthalmic practitioners14 and the other was a survey study used to estimate the fraction of the Australian population that used contact lenses.15
The nonrandomized studies included in this report consisted of 2 cross-sectional studies: Bokhary et al. (2022)16 and González-Pérez et al. (2019).17
No guidelines that formulated evidence-based recommendations for refractive laser surgery were identified.
The SR by Wu et al. (2020)13 was conducted in Australia. It included a population-based estimate of the percentage of contact lens users and associated safety in Australia; LASIK safety data were obtained from the US FDA database of RCTs. The countries where the RCTs were conducted were not reported.
The study by Bokhary et al. (2022)16 was conducted in Saudi Arabia. The cross-sectional study by González-Pérez et al. (2019)17 was conducted in 1 university and 1 ophthalmology clinic in Spain.
The SR13 included data from 4,882 eyes from participants in LASIK RCTs, representing an unreported number of individuals older than either 18 or 21 years depending on the study with a wide range of refractive errors ranging from 6 diopters (D) to −15 D. Of the 19 included RCTs, 10 studies included participants with astigmatism up to 8 D.13 Additional data were obtained from an Australian surveillance study, published in 2008, of all contact lens–related vision loss cases over the course of 12 months in people aged between 15 and 64 years who wore contact lenses14 as well as from a telephone survey study published in 2014 on the proportion of contact lens users among the general Australian population.15
The 2 nonrandomized studies included in this report were cross-sectional studies in which participants were examined at a single time point in a hospital setting. The study by Bokhary et al. (2022)16 included participants aged between 19 and 40 years with a myopia spherical equivalent (SE) of 10.5 D or less, hyperopia SE of 4.50 D or less, and astigmatism of 6.00 D or less. Participants with ocular pathology, prior ocular surgery, pre-presbyopia, or who were taking medication were excluded; however, the latter criteria were not further defined. In this study, 51 participants were not planning to undergo PRK, 50 participants were going to undergo PRK and had stable refraction for at least 1 year (pre-PRK group), and 44 participants had received PRK within the past 5 years (post-PRK group). The participants in the post-PRK group were further stratified by how long it had been since they received PRK: 1 week (n = 13), 1 week to less than or equal to 6 months (n = 16), or greater than 6 months (n = 15). The groups of participants were similar with regard to sex but significantly different in age and uncorrected distance visual acuity. The majority of the study participants living in Saudi Arabia used spectacles alone (control group: 86.3%; pre-PRK group: 78.0%) for vision correction as opposed to contact lens or spectacles and contact lens. Of all participants, 98.6% had myopia.16 González-Pérez et al. (2019)17 examined 4 groups of 24 participants each: participants with eyes that were emmetropic, participants with myopia and had undergone LASIK surgery 12 months prior, participants who used continuous wear silicone-hydrogel (Si-H) contact lenses for 12 months, and patients who had worn corneal refractive therapy (CRT) lenses for 12 months. The mean SE ranged from −2.04 D to −2.91 D; all participants who wore contact lenses had myopia. The groups participated at 1 university and 1 ophthalmology clinic. Any differences in mean age, sex, and SE were not statistically significant.17
The intervention arm of the SR comprised an MA of RCTs on various LASIK systems for the correction of refractive errors. The primary control of the RCT data was reported as the preoperative state of the treated eye. Wu et al. (2020)13 did not provide more details about the study design of the RCTs and did not use the control arm data from the RCTs. The comparators examined were any contact lens type, daily wear contact lenses, overnight soft contact lenses, and overnight wear Si-H contact lens. The rates of contact lens usage and associated vision loss were obtained from published Australian epidemiological surveys.13-15
The intervention of interest in the cross-sectional study by Bokhary et al. (2022)16 was PRK for the correction of refractive error. Two control groups were enrolled in this study; 1 group who intended to correct their refractive error by PRK (pre-PRK) and another group who used conventional vision correction technologies (prescription glasses and/or contact lenses) and did not intend to correct their refractive error by any refractive surgical intervention. The study by González-Pérez et al. (2019)17 included participant groups whose refractive error had been successfully corrected with LASIK with the Wavelight Allegretto Wave Eye-Q (Wavelight GmbH, Germany), CRT orthokeratology lenses (Paragon, AZ), or continuous wear (30 nights during 12 months) lotrafilcon A Si-H contact lenses (Alcon Pharmaceuticals Ltd., Switzerland). A participant group with eyes that were emmetropic and who had never used visual correction was also included as a control group.
The SR13 estimated the frequency of vision loss events per eye associated with vision correction by LASIK compared with contact lens use. Loss of vision from LASIK was all-cause vision loss at 6-month follow-up, whereas all incidents from Australia of vision loss over the course of 12 months related to contact lens use was from participants after contact lens–related microbial keratitis. In both cases, vision loss was defined as a loss of 2 or more lines of best spectacle-corrected visual acuity and these rates were stratified by contact lens type and duration of wear. The results were also used to derive the number of years of contact lens wear equivalent to the one-off risk associated with LASIK. The authors suggested this vision loss outcome provided better context than prior studies in which vision loss following a LASIK procedure was reported only as a result of microbial keratitis. The authors did not provide data on causes of vision loss captured in the RCTs. Although only vision loss following microbial keratitis was included for the contact lens use group, the authors acknowledged this limitation and suggested that other causes of contact lens–related vision loss are very rare with supporting references.13
Bokhary et al. (2022)16 reported uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), as measured by a Snellen chart in which 0 D represented perfect vision. SE, as measured by autorefractometer, and central corneal thickness, as measured by Scheimpflug imaging (Pentacam HR, Oculus Inc., WA), were also reported.
Results from the Quality of Life Impact of Refractive Correction (QIRC) administered at a single time point were also reported by Bokhary et al. (2022).18 This subjective patient-reported outcome measure used a response scale in 5 categories and a “not applicable” response and was linearly converted to a score from 0 to 100 with higher numbers indicating higher QoL. The QIRC used by Bokhary et al. (2022)18 was translated into Arabic from the English version and validated using Rasch analysis. An overall QIRC score was reported for each participant group, although a minimal clinically important difference (MCID) was not reported. Results for each of the 20 questions, and results for the 6 domains of the QIRC were also reported.16 The study by González-Pérez et al. (2019)17 reported the overall score and domain subscore means of the National Eye Institute Refractive Error Quality of Life Instrument (NEI RQL-42) administered to participants at a single time point. This instrument is a validated survey that consists of 42 questions to assess 13 different vision-related QoL domains. Each question is scored from 1 to 100, with higher numbers reflecting greater QoL. These numbers were reported without the context of a MCID.
The SR13 included in this report provided an MA of RCTs on LASIK systems identified in the FDA database, although it did not analyze comparative findings of the included RCTs. The SR extracted the incidence of vision loss from the identified literature; however, this narrow objective was not well suited to conduct a methodologically comprehensive SR. The SR lacked critical domains of the AMSTAR 2 criteria and, consequently, critically low confidence was associated with the findings in Wu et al. (2020).13 The AMSTAR 2 criteria that were lacking or absent from the SR were a clearly formulated research question, prior establishment of review methods, a comprehensive literature search, literature selection criteria, duplicate literature selection and data extraction, justification for only using RCTs, information on excluded studies, critical appraisal of included studies, justification for combining trial data, assessment of publication bias, and a discussion of study limitations. The study did report a potential conflict of interest. The most obvious methodological concern that increased the potential for bias was the potential differences between populations that participated in the RCTs and the populations from which the incidence of vision loss associated with contact lens use was estimated. The SR did not provide any comparison between these 2 populations. Similarly, the outcome for vision loss for LASIK participants was all-cause, whereas the vision loss for contact lens users was as a result of microbial keratitis. The SR did report limited methodology for a systematic literature search and selection, data extraction, a summary of included studies, the funding source of included studies, and a defined follow-up period; however, based upon the aforementioned limitations, the SR could not be relied upon to provide an accurate and comprehensive summary of the risk of vision loss identified by the included LASIK studies. The confidence in conclusions regarding the risk of vision loss associated with LASIK compared with contact lens use included additional low-quality evidence and therefore was also rated as critically low.13
The nonrandomized studies16,17 included in this report used a cross-sectional, observational design. These studies had all the limitations associated with this approach, the most significant of which was difficulty in determining the degree of causality between the intervention and observed outcomes. Furthermore, neither study provided justification for the sample size; therefore, findings that lacked a statistical difference between groups did not support any conclusions. Neither study reported any findings with respect to a MCID that made a statistically significant difference of unknown clinical relevance.16,17 Bokhary et al. (2022)16 did not report 1 visual acuity outcome (SE) for all groups of participants; it was only reported for subgroups of 1 participant group. Bokhary et al. (2022)16 used a Kruskal-Wallis test for statistical significance for the QoL questionnaire, which did not identify which individual group differences were statistically significant. This made interpretation challenging because this study had 2 untreated participant groups.
Despite these limitations, both studies16,17 had methodological strengths, as described in AXIS.11 Neither study was a broadly disseminated survey with a large percentage of nonrespondents, as is typical for cross-sectional studies, and both recruited participants with defined inclusion and exclusion criteria. Both studies examined objective outcomes using validated patient-reported outcomes, had a clear study objective, reported patient characteristics, statistical methodology was reported, conclusions were justified, a discussion of limitations was provided, ethics approval was obtained, and both had a statement that the study had no potential conflict of interest.16,17 Both studies16,17 reported statistically significant age differences between groups, and Bokhary et al. (2022)16 identified differences in UDVA between the participant groups. Bokhary et al. (2022)16 did not report relevant methodology but did provide some limited longitudinal CDVA data for post-PRK participants.16 Overall, the strengths of these studies remained limited by the cross-sectional study design and the findings were at high risk of bias.
Additional details regarding the strengths and limitations of included publications are provided in Appendix 3.
Appendix 4 presents the main study findings.
Bokhary et al. 202216 reported UDVA and CDVA in 3 groups of participants: a control group that used conventional vision correction with no intention of undergoing refractive surgery, a group planning on undergoing PRK (pre-PRK), and a group that had undergone PRK (post-PRK). Without refractive correction, including before correction for the post-PRK group, there was a statistical difference in visual acuity among the 3 groups. The control group had the highest visual acuity followed by the pre-PRK group; the post-PRK had the lowest visual acuity. When the participants used conventional vision correction, or after PRK in the post-PRK group, there was no statistical difference in visual acuity. The subgroups of participants in the post-PRK group had statistically significant differences in CDVA and those participants who had PRK more than 6 months prior had greater visual acuity. The authors stated that PRK requires a longer recovery than LASIK, and the corneal epithelial layer can take as long as 2 weeks to heal, which could explain the differences among the post-PRK subgroups.16
The measure of astigmatism, SE of manifest refraction, was obtained from all 145 participants but was only reported for the 44 post-PRK participants. Participants at 1 week (n = 13), at less than or equal to 6 months (n = 16), and greater than 6 months following PRK (n = 15) demonstrated statistically significant differences with the participant groups examined at later intervals having less refractive error due to astigmatism.16
The 2 cross-sectional studies16,17 reported results of QoL self-assessments from different groups of study participants. Bokhary et al. (2022)16 found a statistically significant difference in the overall QIRC score between groups. Participants who had undergone PRK had the highest QIRC score (mean = 53.84; standard deviation [SD] = 7.14), while the scores of the control group and the pre-PRK group were 45.79 (SD = 7.15) and 43.68 (SD = 5.69), respectively.16 Individual scores within the convenience, well-being, and health concern domains of the QIRC were statistically significantly higher for participants in the post-PRK group than those for participants in the control and pre-PRK group. No statistically significant differences were identified among the post-PRK subgroups of 1 week, 1 week to 6 months, and greater than 6 months.16 Individual QoL scores of the QIRC are summarized in Table 7 of Appendix 4.
González-Pérez et al. (2019)17 found a statistically significant difference in the NEI RQL-42 overall score for participants who wore Si-H contact lenses of (mean = 87.1; SD = 6.4) compared with participants who had undergone LASIK 12 months prior (mean = 80.0; SD = 10.2). The authors attributed this overall difference as a summation of differences in subscores that evaluated diurnal fluctuations, glare, expectations, and worry aspects of QoL. However, only differences in worry, symptoms, and expectation QoL subscores were statistically significant in isolation. No other statistically significant differences were identified between the participant groups that had undergone refractive surgery and those who used conventional vision correction. The authors interpreted their findings as continuous wear Si-H contact lenses were associated with the highest global QoL scores and LASIK was associated with the lowest scores.17
Neither study provided context for the identified differences with respect to a MCID.16,17
The SR13 reported the incidence of all causes of vision loss, defined as the loss of 2 or more lines of best spectacle-corrected visual acuity, associated with LASIK procedures and contact lens use. The MA of 19 RCTs identified the rate of vision loss at 6 months after LASIK as 66 events per 10,000 eyes (95% confidence interval [CI], 34 to 108 events per 10,000 eyes). The authors also extracted data from a previously published Australian surveillance study by Stapleton et al. (2008)14 that identified an annualized incidence of vision loss of 0.28 per 10,000 eyes (95% CI, 0.28 to 0.31 per 10,000 eyes) associated with contact lens use.13 The extracted data were used to calculate the number of years of contact lens use that presented an equivalent risk of vision loss associated with the single 6-month risk following LASIK. Across all contact lens types, 218 years (95% CI, 103 to 391 years) of wear presented the same risk of vision loss as LASIK. Overnight soft contact lenses presented 31 risk-equivalent years (95% CI, 16 to 51 risk-equivalent years), overnight wear Si-H contact lens presented 48 risk-equivalent years (95% CI, 25 to 79 risk-equivalent years), and daily wear soft contact lenses presented 320 risk-equivalent years (95% CI, 165 to 525 risk-equivalent years). The authors formulated cautious comparative conclusions based on the data, including that individual risk is low with either LASIK or contact lenses.13
The comparative evidence identified in this report consisted of 1 SR and 2 cross-sectional studies that were evaluated as at high risk of bias. The critical appraisal of the SR was limited by the less conventional objective of the included SR, in which additional low-quality data were combined with the MA data for the comparative outcome analysis. Although addressed narratively in this report, the standard criteria of the AMSTAR2 critical appraisal tool did not account for the addition of other unsystematically selected low-quality data. The studies included in this report consisted of undefined populations from RCTs in Australia, Saudi Arabia, and Spain, and the relevance of this evidence for patients with vision conditions in a Canadian setting is therefore unclear. Additionally, the participants examined for visual acuity and QoL outcomes in the identified evidence almost exclusively had myopia, and the relevance to people with related refractive errors, including hyperopia and astigmatism, is unknown. This report did not identify any evidence of sufficient quality to inform decision- or policy-making. It is unknown if any high-quality studies that compared refractive laser surgeries to conventional vision correction technologies are forthcoming. In addition, this report did not identify any evidence-based guidelines that provided recommendations for best practices when considering refractive laser surgery for people with vision conditions.
This report identified 1 SR and 2 cross-sectional studies published since 2018 that examined the clinical effectiveness of refractive laser surgery compared with conventional vision correction technologies for people with vision conditions.13,16,17
As reported by Bokhary et al. (2022),16 statistically significant differences in corrected visual acuity outcomes were not identified between participants who did not intend to have PRK, participants who had not yet undergone PRK, and participants who had undergone PRK within the past 5 years. This study had significant limitations inherent to the cross-sectional design, may have been insufficiently powered to detect differences between groups, and uncorrected visual acuity and age differed between participant groups. This study found participants at later follow-up times after PRK had increased visual acuity; however, no baseline data were provided for these subgroups of fewer study participants. Inferences for comparative visual acuity outcomes for PRK compared with conventional vision correction technologies were not apparent based on this evidence.
A prior relevant CADTH report19 including QoL outcomes identified 1 prospective, longitudinal, parallel-group, multicenter survey study of 1,800 adults that compared clinical effectiveness of laser eye surgery to eyeglasses, in a literature search that spanned from January 1, 2013, to May 27, 2018. This survey study, appraised at high risk of bias, found LASIK patients reported higher overall patient satisfaction compared with those who wore contact lenses. This study also found that a greater proportion of participants who wore contact lenses reported night-driving and night visual disturbances than participants who had undergone LASIK, whereas outcomes such as dry eye, small print reading, depression, eye infection, eye ulcer, and eye abrasion did not differ longitudinally or between participant groups.19
This current report identified 1 cross-sectional study, appraised at high risk of bias, that found participants who had undergone PRK reported higher overall vision-related QoL, better driving in glare conditions, and better QoL in domains of convenience, health concerns, and well-being compared with participants who were using conventional corrective lenses.16 In contrast, the other cross-sectional study identified in this report,17 also appraised at high risk of bias, did not identify any significant difference in a satisfaction subscore of a QoL questionnaire between participants who had a LASIK procedure and those who wore contact lenses. Furthermore, this study found that participants who wore conventional contact lenses reported greater overall QoL, reported as a summation of statistically significant differences in QoL subscores of worry, symptoms, and expections.17 An interpretation of the conflicting QoL findings between these studies was not possible. Although different vision-related QoL questionnaires were used in each study, all conclusions were associated with very low confidence based on the appraised risk of bias.16,17,19
The SR by Wu et al. (2020)13 reported on vision loss outcomes, and it was also appraised at a high risk of bias for this report. Although the findings of risk associated with LASIK and contact lenses were based upon different populations of unknown clinical comparison, the magnitude of the findings suggested there is a greater risk of vision loss with LASIK in the setting of a clinical trial compared with contact lens use in the general population. The authors suggested that the results support a low risk of vision loss to an individual with either LASIK or contact lens use.13 Any interpretation of the evidence identified in this report should be made with caution due to a lack of high-quality evidence. The literature screening process suggested the current literature is primarily focused on comparisons between different refractive laser surgery procedures without direct comparisons with conventional vision correction technologies, and it is unclear if relevant high-quality comparative evidence is forthcoming.
A Measurement Tool to Assess Systematic Reviews 2
Appraisal tool for Cross-Sectional Studies
corrected distance visual acuity
confidence interval
corneal refractive therapy
laser-assisted in situ keratomileusis
meta-analysis
minimal clinically important difference
National Eye Institute Refractive Error Quality of Life Instrument
photorefractive keratectomy
Quality of Life Impact of Refraction Correction
quality of life
standard deviation
spherical equivalent
systematic review
randomized clinical trial
uncorrected distance visual acuity
Selection of Included Studies.
Note that this appendix has not been copy-edited.
Characteristics of Included Systematic Review.
Characteristics of Included Primary Clinical Study.
Note that this appendix has not been copy-edited.
Strengths and Limitations of Systematic Review Using AMSTAR 2.
Strengths and Limitations of Clinical Studies Using the AXIS Checklist.
Note that this appendix has not been copy-edited.
Summary of Findings by Outcome — Visual Acuity.
Summary of Findings by Outcome — QIRC Scores.
Summary of Findings by Outcome — NEI RQL-42 Scores.
Summary of Findings by Outcome — Vision Loss.
Note that this appendix has not been copy-edited.
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