Introduction

A definitive presbyopia correction technique is one of the main challenges for refractive surgeons nowadays, which must deal with patients with increasingly demanding visual requirements. A large proportion of myopic and hyperopic subjects, with or without astigmatism and with or without cataract, search for spectacle independence at any age, and accordingly, different types of techniques have been developed to overcome the near and intermediate visual difficulties associated to each age range. Presbyopia-correcting IOLs are increasing its visibility on clinical practice in the case of pseudophakic subjects in which the accommodative ability has been reduced or is absent, but in the case of young presbyopes with a remaining accommodative function, other techniques seem to be more appropriate than removing a functional and clear lens [1].

PresbyLASIK is a refractive technique in which the corneal shape is ablated with a multifocal profile, that is with a multiaspheric ablation to provide acceptable focus for distance, intermediate and near vision [2]. Different laser manufacturers have developed their own algorithms to create this multifocal profile, and accordingly different trade names have been assigned depending on the manufacturer: Supracor (Technolas Perfect Vision GmbH), Presbyond (Carl Zeiss Meditec GmbH), PresbyMax (SCHWIND eye-tech-solutions GmbH), or Custom Q (Alcon Laboratories Inc.) (Fig. 1) [3]. Some of these algorithms are programmed based on the target near addition or planned according to the subject’s age, but the effective change on refraction comes from the controlled change in the corneal asphericity from the center to the periphery, depending not only on the magnitude of near addition but also on the distance vision ablation profile (if myopic or hyperopic). Additionally, two more variants have to be considered since presbyLASIK can be central when the near vision profile is applied in the central cornea, or peripheral, when it is applied peripherally [4]. All these combinations provide a wide range of refractive options for presbyopic patients, with the additional possibility of combining a multiaspheric profile in one eye and a conventional profile in the fellow eye, generating some level of myopia and consequently some level of monovision. This wide range of options makes difficult to know the real impact of a specific multiaspheric ablation profile without the interference of factors such as the induction of micro-monovision. The aim of the current investigation was to review the scientific literature about the efficacy of presbyLASIK in myopic and hyperopic presbyopes, analysing the quality of the scientific evidence associated to this technique, the bias sources of the studies revised and to determine the requirements of future studies evaluating the clinical outcomes of this surgical option of correction of presbyopia.

Fig. 1
figure 1

Main characteristics of the four main platforms of presbyLASIK that are commercially available.

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Methods

A search equation including the following terms was conducted in PubMed database: PresbyLASIK OR PresbyMax OR Presbyond OR Presbyone OR Custom Q. Additionally, the following specific selection criteria were applied as a search filter:

  1. (i)

    Original articles.

  2. (ii)

    Articles in English.

  3. (iii)

    Articles since 2010.

Titles and abstracts were reviewed from this first search, and only those articles whose aim was to evaluate the visual outcomes of presbyLASIK technique in presbyopic subjects were considered. Optical simulations or case reports were excluded. Duplicates were also excluded. In a second step, complete texts were reviewed to confirm the selection criteria applied. Manual search brought us back an additional article that was included afterwards.

Quality assessment of publications was performed by two methods depending on the type of study [5, 6]. The higher level of scientific evidence was represented by non-randomized clinical trials, that is prospective interventional studies, using for this type of studies the tool ROBINS-I to assess the risk of bias, as recommended [7]. At protocol stage, the review question was to evaluate presbyopic subjects (participants) operated on with presbyLASIK (experimental intervention) in comparison to monovision (comparator) for visual acuity (VA), refraction, quality of vision, spectacle independence, aberrations, or contrast sensitivity (outcomes). The aim for these studies was to assess the effect of assignment to intervention. The ROBINS-I is a tool developed to assess risk of bias in the results of non-randomized studies that compare health effects of two or more interventions. Specifically, the following bias domains are evaluated:

  • Pre-intervention: bias due to confounding and bias in selection of participants into the study.

  • At intervention: bias in classification of interventions.

  • Post-intervention: bias due to deviations from intended interventions, bias due to missing data, bias in measurement of outcomes, and bias in selection of the reported result.

After answering the different questions used to evaluate these domains, an overall evaluation is provided as follows: low risk of bias (the study is judged to be at low risk of bias for all domains), moderate risk of bias (he study is judged to be at low or moderate risk of bias for all domains), serious risk of bias (the study is judged to be at serious risk of bias in at least one domain, but not at critical risk of bias in any domain), and critical risk of bias (the study is judged to be at critical risk of bias in at least one domain).

The main body of the scientific evidence recruited in this search was represented by case series, that is prospective or retrospective observational studies with limited groups of participants in most of cases. For these studies, the 20-criterion quality appraisal checklist described by Moga et al. [8] was applied to evaluate this type of evidence. This tool examines different items evaluating the execution of the study (aim, recruitment, description of characteristics of subjects, inclusion criteria, definition of the intervention, blinding of assessors, follow-up, methodology, adverse events, conclusions, or competing interests) but also the quality of the reporting (clear definition of main outcomes measures and statistical tests) [9]. Depending on the number of positive responses (YES in front of PARTIAL/UNCLEAR or NO), a score is assigned. Before using the checklist, the relevant aspects should be addressed by the assessors. Summary of the applied criteria in this study is represented in Fig. 2.

Fig. 2: Criteria used for quality assessment with the 20-criterion quality appraisal checklist defined by Moga et al. [8].
figure 2

Studies may provide this specific information to receive the positive rating (YES).

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Results

The search was conducted on 13th of May, 2021. Following the search equation described, a total of 42 articles were identified, including four articles in other languages that were excluded. After applying the selection criteria, 22 articles were selected for a more comprehensive evaluation with the selected tools. A manual search included an additional article, and therefore 23 articles were finally included: 2 non-randomized controlled clinical trials (NRCT) [10, 11] and 21 case series studies [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]. Figure 3 shows the flow chart followed during the search. The main causes of exclusion were nine articles that were reviews of the previous literature, and eight articles with no access to full text. Main characteristics of the articles finally included in the systematic analysis are summarized in Tables 1, 2. As shown in Table 2, different types of ablation profiles of different excimer laser platforms have been used in the articles revised.

Fig. 3
figure 3

Flow chart of the selection process of relevant articles that were included in the current systematic review.

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Table 1 Summary of main studies characteristics.
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Table 2 Characteristics of the laser ablation profile or mode used in the different studies revised in the current systematic review.
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The quality and risk of bias of the revised articles was obtained and summarized following the guidelines of each evaluation tool in Table 3 (for ROBINS-I) and Table 4 (for Moga tool). For NRCT, the risk of bias was moderate in one study [10] and serious in the other NRCT [11], being the main source of risk the domains related to confounding, selection of participants and measurement of outcomes (Table 3). For case series studies [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32], the main sources of risk of bias was subjects not entering the study at the same point of the conditions (different levels of presbyopia) (14 “No” answers from the 21 articles evaluated) (Table 4), and the inclusion of cases collected from different centers (17 “No” answers from the 21 articles evaluated). The answer “Partial” was reported for half of the articles revised or more in the following items: establishment a priori of relevant outcome measures (10/21) and report of both competing interests and sources of support of the study (13/21). Likewise, there was a significant level of uncertainty for a large proportion of the studies revised for the following items: consecutive recruitment of patients (12 unclear answers/21), blinding of outcome assessors to the intervention that the patient received (21 unclear answers/21), and conclusions of the study not supported by the results (6 unclear answers/21).

Table 3 Summary of the results obtained by ROBINS-I tool for risk of bias assessment for non-randomized clinical trials.
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Table 4 Summary of the results of 20-criterion quality appraisal checklist tool for case series assessment developed by Mogaetal.
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Discussion

The induction of controlled amounts of primary spherical aberration has been shown to be an effective option to expand the depth of focus (DOF) of the eye and consequently to provide a functional correction of vision across different distances for presbyopes [33]. Likewise, the induction of some level of other types of high order aberrations (HOAs), such as secondary spherical aberration or primary coma, has also shown a positive impact on the enlargement of the DOF [34, 35]. This aberrometric induction can be generated at the corneal plane by means of an excimer laser which was the initial concept of presbyLASIK [4]. However, this technique has been modified continuously with aim of maximizing the level of DOF achieved and minimizing the level of spectacle independence [5]. This evolution has led to the combination of a multiaspheric profile inducing a controlled amount of HOAs with the concept of micro-monovision, which consists of leaving a small myopic residual refraction in the non-dominant eye. The question is if this procedure can be still considered or called presbyLASIK or if it is modified version of the monovision concept. Likewise, there are several combinations that have been proposed but their real clinical benefit is still unclear: multiaspheric profile in both eyes (classical or symmetric presbyLASIK), multiaspheric profile in both eyes with additional micro-monovision in the non-dominant eye (bilateral presbyLASIK combined with µ-monovision), different multiaspheric profiles (different addition) in both eyes (asymmetric bilateral hybrid presbyLASIK), a conventional monofocal ablation profile in the dominant eye and multiaspheric profile in the non-dominant eye (asymmetric monocular mode presbyLASIK). The aim of the current study was to revise systematically the published research on presbyLASIK to know the real evidence associated to this technique, its risk of bias, if there are sufficient evidence of the benefit of one specific combination over the other ones, and how the scientific evidence on this technique can be consistently improved.

In the bibliographic search performed, only two NRCTs were found in which central presbyLASIK was applied. Kohnen et al. [10] performed a comparison of two types of presbyLASIK techniques: 15 patients treated with bilateral presbyLASIK combined with µ-monovision and 15 patients treated with asymmetric bilateral hybrid presbyLASIK. These authors found that the hybrid and µ-monovision groups did not differ significantly except for distance-corrected near visual acuity, with a better outcome in those eyes treated with presbyLASIK combined with µ-monovision (0.21 ± 0.15 logMAR vs. 0.34 ± 0.17 logMAR). This trial showed a moderate bias due to selection of participants and measurement of outcomes, with no inclusion of a control group using a conventional ablation profile with or without monovision approach. The second NRCT included in the current systematic review was conducted by Leray et al. [11] in which the dominant eye was operated using a conventional profile and the non-dominant eye was programmed with an aspheric ablation profile and −0.75 D of residual refractive error. These authors concluded that aspheric hyperopic LASIK could increase the DOF without impairing far vision, but this conclusion should be taken with care as the increase of DOF cannot be attributed exclusively to the induction of spherical aberration because a myopic residual refractive error was present in all patients. This leads to a serious level of bias due to confounding variables.

Concerning the case series, as shown in Table 4, all studies showed one or more sources of bias, being subjects not entering the study at the same point of the conditions (different levels of presbyopia) and no inclusion of cases collected from different centers among the most detected. Likewise, some conditions to avoid bias was partially accomplished in most of the case series revised, especially in terms of establishment a priori of relevant outcome measures and report of both competing interests and sources of support of the study. Furthermore, some conditions leading to bias were not clearly identified in these case series, such as a non-consecutive recruitment of patients, not blinding of outcome assessors to the intervention that the patient received, and the description of some conclusions not fully supported by the results. It should be considered that all these series reported an improvement in intermediate and near visual performance after the laser intervention, but without a control group to compare.

Most of articles on presbyLASIK are focused on reporting the outcomes of central presbyLASIK [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32], with very limited research on peripheral presbyLASIK [36, 37]. As most of articles on this technique were published several years ago and the current research on this issue is focused on central presbyLASIK, it can be hypothesized that some limitations could be present in peripheral presbyLASIK. However, there are no comparative studies of both techniques confirming this issue. Pinelli et al. [36] reported a mean binocular uncorrected decimal visual acuity of 1.06 ± 0.13 for distance and 0.84 ± 0.14 for near at 6 months after peripheral presbyLASIK, with a decrease of contrast sensitivity for the spatial frequencies of 3, 6, 12, and 18 cycles/degree. Epstein and Gurgos [37] investigated the outcomes of monocular peripheral presbyLASIK on the non-dominant eye with distance-directed monofocal refractive surgery on the dominant eye, reporting the achievement of complete spectacle independence in 89% of hyperopes and 92% of myopes. However, these authors did not measure the defocus curve to assess the level of visual functionality achieved and the impact on visual quality was not fully investigated.

The research on presbyLASIK shows significant weaknesses and biases that should be avoided in future trials. First, more controlled comparative studies are needed to obtain consistent conclusions about the real clinical benefit of this technique over the use of a conventional ablation profile to correct the refractive error inducing a specific level of monovision. Second, as is commonly performed in articles reporting the outcomes of presbyopia-correcting IOLs, some results and analyses should be mandatory for reporting the outcomes of any type of presbyLASIK technique, including the defocus curve, the measurement on uncorrected and distance-corrected intermediate and near visual acuity and the analysis of contrast sensitivity to confirm the real impact on visual quality. Furthermore, the evaluation of the binocular vision, with specific analysis of the impact on sensorial fusion and stereopsis, must be performed in any study evaluating the results of an asymmetric presbyLASIK approach with different types of correction in each eye. Likewise, comparative studies of the results of presbyLASIK and the outcomes with different types of presbyopia-correcting IOLs, including trifocal or extended depth of focus IOLs, should be also performed in the near future to understand better the role of this therapeutic option on presbyopia.

In conclusion, research on presbyLASIK to this date is mainly focused on case series generating a limited level of scientific evidence. The two non-randomized clinical trials identified only demonstrated the potential benefit of combining the multiaspheric profile with some level of monovision in the non-dominant eye for inducing an enhanced near visual performance. Future controlled clinical trials are needed to provide more consistent evidence of the benefit or equivalence of this therapeutic option over other options for compensation of presbyopia.

Summary

What was known before

  • PresbyLASIK is a refractive technique in which the corneal shape is ablated with a multifocal profile, that is with a multiaspheric ablation to provide acceptable focus for distance, intermediate and near vision in presbyopia.

  • Different laser manufacturers have developed their own algorithms to create their own presbyLASIK multifocal profile.

  • Different studies have been conducted to show the results of this option of presbyopia correction with different laser platforms.

What this study adds

  • Research on presbyLASIK to this date is provided a limited level of scientific evidence as it is mainly focused on case series.

  • Two non-randomized clinical trials have been performed that have demonstrated the combination of the multiaspheric profile with some level of monovision in the non-dominant eye generates a satisfactory outcomes.

  • More controlled comparative studies are needed to obtain consistent conclusions about the real clinical benefit of this technique over a monofocal ablation as well as about the real differences between the different presbyLASIK options that are currently available.