Novel Technique of Transepithelial Corneal Cross-Linking Using Iontophoresis in Progressive Keratoconus

Assessment of the Predictive Ability of Theranostics for Corneal Cross-linking in Treating Keratoconus: A Randomized Clinical Trial

PURPOSE

To validate the ability of theranostic imaging biomarkers in assessing corneal cross-linking (CXL) efficacy in flattening the maximum keratometry (Kmax) index.

DESIGN

Prospective, randomized, multicenter, masked clinical trial (ClinicalTrails.gov identifier, NCT05457647).

PARTICIPANTS

Fifty patients with progressive keratoconus.

INTERVENTION

Participants were stratified to undergo epithelium-off (25 eyes) and epithelium-on (25 eyes) CXL protocols using an ultraviolet A (UV-A) medical device with theranostic software. The device controlled UV-A light both for performing CXL and assessing the corneal riboflavin concentration (riboflavin score) and treatment effect (theranostic score). A 0.22% riboflavin formulation was applied onto the cornea for 15 minutes and 20 minutes in epithelium-off and epithelium-on protocols, respectively. All eyes underwent 9 minutes of UV-A irradiance at 10 mW/cm2.

MAIN OUTCOME MEASURES

The primary outcome measure was validation of the combined use of theranostic imaging biomarkers through measurement of their accuracy (proportion of correctly classified eyes) and precision (positive predictive value) to classify eyes correctly and predict a Kmax flattening at 1 year after CXL. Other outcome measures included change in Kmax, endothelial cell density, uncorrected and corrected distance visual acuity, manifest spherical equivalent refraction and central corneal thickness 1 year after CXL.

RESULTS

Accuracy and precision of the theranostic imaging biomarkers in predicting eyes that had >0.1 diopter (D) of Kmax flattening at 1 year were 91% and 95%, respectively. The Kmax value significantly flattened by a median of -1.3 D (IQR, -2.11 to -0.49 D; P < 0.001); both the uncorrected and corrected distance visual acuity improved by a median of -0.1 logarithm of the minimum angle of resolution (logMAR; IQR, -0.3 to 0.0 logMAR [P < 0.001] and -0.2 to 0.0 logMAR [P < 0.001], respectively). No significant changes in endothelial cell density (P = 0.33) or central corneal thickness (P = 0.07) were noted 1 year after surgery.

CONCLUSIONS

The study demonstrated the efficacy of integrating theranostics in a UV-A medical device for the precise and predictive treatment of keratoconus with epithelium-off and epithelium-on CXL protocols. Concentration of riboflavin and its UV-A light mediated photoactivation in the cornea are the primary factors determining CXL efficacy.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Management of keratoconus: an updated review

Keratoconus is the most common corneal ectatic disorder. It is characterized by progressive corneal thinning with resultant irregular astigmatism and myopia. Its prevalence has been estimated at 1:375 to 1:2,000 people globally, with a considerably higher rate in the younger populations. Over the past two decades, there was a paradigm shift in the management of keratoconus. The treatment has expanded significantly from conservative management (e.g., spectacles and contact lenses wear) and penetrating keratoplasty to many other therapeutic and refractive modalities, including corneal cross-linking (with various protocols/techniques), combined CXL-keratorefractive surgeries, intracorneal ring segments, anterior lamellar keratoplasty, and more recently, Bowman's layer transplantation, stromal keratophakia, and stromal regeneration. Several recent large genome-wide association studies (GWAS) have identified important genetic mutations relevant to keratoconus, facilitating the development of potential gene therapy targeting keratoconus and halting the disease progression. In addition, attempts have been made to leverage the power of artificial intelligence-assisted algorithms in enabling earlier detection and progression prediction in keratoconus. In this review, we provide a comprehensive overview of the current and emerging treatment of keratoconus and propose a treatment algorithm for systematically guiding the management of this common clinical entity.

Topographic Outcomes in Keratoconus Surgery: Epi-on versus Epi-off Iontophoresis Corneal Collagen Cross-Linking

Background: Corneal collagen cross-linking (CXL) has become the gold standard for mild and moderate stages to stop the progression of keratoconus. We analyzed some corneal topography indices to compare iontophoresis epi-on and iontophoresis epi-off techniques throughout a two-year follow-up. Methods: A total of 64 eyes of 49 patients who underwent CXL were recruited. In 30 eyes the epi-off technique was performed, whereas the remaining 34 eyes were treated with the epi-on technique. All patients underwent a complete ophthalmologic examination that included CDVA, central and thinnest corneal thickness, Schirmer test I, TBUT test, and the Ocular Surface Disease Index. Results: In both groups, a significant improvement in visual function was recorded. No statistically significant differences between Kmax, Mean K, Flat K, Steep K values were found. Statistically significant differences (p < 0.05) between the epi-on and epi-off groups’ pachymetry before and after 24 months follow-up as well as between the epi-on and epi-off groups’ topographically thinnest point in the immediate post-surgery and 24 months after surgery were recorded. Conclusion: Our study highlighted that both techniques are valid in mid-term corneal stabilization. The advantage of the new iontophoresis epi-off cross-linking technique could be found in a faster imbibing time of the cornea, therefore reducing surgical times, with a lower risk of complications.

Transepithelial Versus Epithelium-Off Corneal Crosslinking for Progressive Keratoconus: Findings From a Cochrane Systematic Review

PURPOSE

The purpose of this study was to summarize key findings from a systematic review of the effectiveness and safety of transepithelial corneal crosslinking (CXL) compared with epithelium-off CXL for progressive keratoconus.

DESIGN

Cochrane systematic review.

METHODS

We included in our review only randomized controlled trials (RCTs) in which transepithelial and epithelium-off CXL had been compared among participants with progressive keratoconus. The primary outcome was keratoconus stabilization based on post-operative maximum keratometry (Kmax). We adhered to Cochrane methods for trial selection, data extraction, risk of bias evaluation, and data synthesis.

RESULTS

Thirteen RCTs with 567 participants (661 eyes) were included; 11 studies compared non-iontophoresis-assisted transepithelial with epithelium-off CXL. Keratoconus stabilization was described as an outcome in 2 studies. The estimated difference in Kmax means (ie, the "mean difference," MD) from meta-analysis of 177 eyes in 5 RCTs indicated that there were no differences between intervention groups in Kmax at 12 months or later (MD: 0.99 diopter [D]; 95% confidence interval: -0.11 to 2.09). Meta-analysis of keratometry and visual acuity outcomes at 12 months or longer after surgery from 2 studies that had compared transepithelial CXL using iontophoresis provided no conclusive evidence of an advantage over epithelium-off CXL.

CONCLUSIONS

Lack of precision due to small sample sizes, indeterminate risk of bias due to inadequate reporting, and inconsistency in how outcomes were measured and reported among studies make it difficult to state with confidence whether transepithelial CXL confers an advantage over epithelium-off CXL for patients with progressive keratoconus with respect to stabilization of keratoconus, visual acuity, or patient-reported outcomes based on available data.

Adverse events after riboflavin/UV-A corneal cross-linking: a literature review

BACKGROUND

Riboflavin/UV-A corneal cross-linking (CXL) for treating keratoconus and iatrogenic corneal ectasia has been well-established as first treatment option to stabilize corneal tissue biomechanical instability. Although the plethora of clinical studies has been published into the field, there is no systematic review assessing the type and frequency of adverse events after CXL.

METHODS

A systemic literature review on clinical safety and adverse events after CXL in patients with keratoconus and corneal ectasia was performed using PubMed. A literature search was performed for relevant peer-reviewed publications. The main outcome measures extracted from the articles were adverse events, endothelial cell density, corrected distance visual acuity and maximum simulated keratometry.

RESULTS

The most frequent adverse events after CXL were corneal haze and corneal edema, which were mild and transient. The severe adverse events were infrequent (cumulative incidence: < 1.3%) after CXL. The clinical benefits of CXL highly outweighed the risks for the treatment of keratoconus and corneal ectasia.

CONCLUSIONS

The severe adverse events with permanent sequelae are infrequent after CXL and all are associated with corneal de-epithelialization, such as infectious keratitis and corneal scarring.

The efficiency and safety of oxygen-supplemented accelerated transepithelial corneal cross-linking

PURPOSE

To investigate the impact of oxygen delivery on the clinical outcomes of accelerated transepithelial corneal cross-linking (A-TE CXL).

METHODS

Fifty-seven eyes of 44 progressive keratoconus (KCN) patients were randomly separated into two age-sex-matched groups. Twenty-nine eyes of 23 KCN patients that underwent oxygen-supplemented A-TE CXL formed the study group and 28 eyes of 21 patients treated with the same procedure but under room air conditions formed the control group. All patients were examined preoperatively, one, six and twelve months after the procedure. The logMAR spectacle-corrected distance visual acuity (CDVA), maximum keratometry (Kmax), mean keratometry, apical posterior keratometry, cylindrical power, minimum central corneal thickness, keratoconus vertex front and back, ocular aberrations, endothelial cell density (ECD), demarcation line depth (DLD) and proportion measures were recorded for statistical analysis.

RESULTS

The preoperative, 1st, 6th and 12th months mean Kmax values of the study group were 55.14 ± 3.99D, 54.85 ± 3.82D, 54.37 ± 3.84D and 54.40 ± 3.86, respectively, and 54.47 ± 3.17D, 54.52 ± 2.97D, 54.25 ± 2.95D and 54.20 ± 2.97 in the control group. The mean Kmax value was decreased significantly more in the oxygen-supplemented group after 12 months compared to the control group (p = 0.019). The mean DLD was also significantly deeper in the study group (320 ± 17 µm) compared to the control group (269 ± 19 µm). There was no significant difference between the two groups in terms of ECD alterations at any of the time intervals (p > 0.05).

CONCLUSION

Keratoconus progression was significantly halted in both groups 12 months after the treatment. In addition, oxygen supplementation during A-TE CXL further significantly increased clinical outcomes compared to room air conditions without any significant change in ECD measures.

Transepithelial versus epithelium-off corneal crosslinking for progressive keratoconus

BACKGROUND

Keratoconus is the most common corneal dystrophy. It can cause loss of uncorrected and best-corrected visual acuity through ectasia (thinning) of the central or paracentral cornea, irregular corneal scarring, or corneal perforation. Disease onset usually occurs in the second to fourth decade of life, periods of peak educational attainment or career development. The condition is lifelong and sight-threatening. Corneal collagen crosslinking (CXL) using ultraviolet A (UVA) light applied to the cornea is the only treatment that has been shown to slow progression of disease. The original, more widely known technique involves application of UVA light to de-epithelialized cornea, to which a photosensitizer (riboflavin) is added topically throughout the irradiation process. Transepithelial CXL is a recently advocated alternative to the standard CXL procedure, in that the epithelium is kept intact during CXL. Retention of the epithelium offers the putative advantages of faster healing, less patient discomfort, faster visual rehabilitation, and less risk of corneal haze.

OBJECTIVES

To assess the short- and long-term effectiveness and safety of transepithelial CXL compared with epithelium-off CXL for progressive keratoconus.

SEARCH METHODS

To identify potentially eligible studies, we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2020, Issue 1); Ovid MEDLINE; Embase.com; PubMed; Latin American and Caribbean Health Sciences Literature database (LILACS); ClinicalTrials.gov; and World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We did not impose any date or language restrictions. We last searched the electronic databases on 15 January 2020.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in which transepithelial CXL had been compared with epithelium-off CXL in participants with progressive keratoconus.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodology.

MAIN RESULTS

We included 13 studies with 723 eyes of 578 participants enrolled; 13 to 119 participants were enrolled per study. Seven studies were conducted in Europe, three in the Middle East, and one each in India, Russia, and Turkey. Seven studies were parallel-group RCTs, one study was an RCT with a paired-eyes design, and five studies were RCTs in which both eyes of some or all participants were assigned to the same intervention. Eleven studies compared transepithelial CXL with epithelium-off CXL in participants with progressive keratoconus. There was no evidence of an important difference between intervention groups in maximum keratometry (denoted 'maximum K' or 'Kmax'; also known as steepest keratometry measurement) at 12 months or later (mean difference (MD) 0.99 diopters (D), 95% CI -0.11 to 2.09; 5 studies; 177 eyes; I² = 41%; very low certainty evidence). Few studies described other outcomes of interest. The evidence is very uncertain that epithelium-off CXL may have a small (data from two studies were not pooled due to considerable heterogeneity (I² = 92%)) or no effect on stabilization of progressive keratoconus compared with transepithelial CXL; comparison of the estimated proportions of eyes with decreases or increases of 2 or more diopters in maximum K at 12 months from one study with 61 eyes was RR 0.32 (95% CI 0.09 to 1.12) and RR (non-event) 0.86 (95% CI 0.74 to 1.00), respectively (very low certainty). We did not estimate an overall effect on corrected-distance visual acuity (CDVA) because substantial heterogeneity was detected (I² = 70%). No study evaluated CDVA gain or loss of 10 or more letters on a logarithm of the minimum angle of resolution (logMAR) chart. Transepithelial CXL may result in little to no difference in CDVA at 12 months or beyond. Four studies reported that either no adverse events or no serious adverse events had been observed. Another study noted no change in endothelial cell count after either procedure. Moderate certainty evidence from 4 studies (221 eyes) found that epithelium-off CXL resulted in a slight increase in corneal haze or scarring when compared to transepithelial CXL (RR (non-event) 1.07, 95% CI 1.01 to 1.14). Three studies, one of which had three arms, compared outcomes among participants assigned to transepithelial CXL using iontophoresis versus those assigned to epithelium-off CXL. No conclusive evidence was found for either keratometry or visual acuity outcomes at 12 months or later after surgery. Low certainty evidence suggests that transepithelial CXL using iontophoresis results in no difference in logMAR CDVA (MD 0.00 letter, 95% CI -0.04 to 0.04; 2 studies; 51 eyes). Only one study examined gain or loss of 10 or more logMAR letters. In terms of adverse events, one case of subepithelial infiltrate was reported after transepithelial CXL with iontophoresis, whereas two cases of faint corneal scars and four cases of permanent haze were observed after epithelium-off CXL. Vogt's striae were found in one eye after each intervention. The certainty of the evidence was low or very low for the outcomes in this comparison due to imprecision of estimates for all outcomes and risk of bias in the studies from which data have been reported.

AUTHORS' CONCLUSIONS

Because of lack of precision, frequent indeterminate risk of bias due to inadequate reporting, and inconsistency in outcomes measured and reported among studies in this systematic review, it remains unknown whether transepithelial CXL, or any other approach, may confer an advantage over epithelium-off CXL for patients with progressive keratoconus with respect to further progression of keratoconus, visual acuity outcomes, and patient-reported outcomes (PROs). Arrest of the progression of keratoconus should be the primary outcome of interest in future trials of CXL, particularly when comparing the effectiveness of different approaches to CXL. Furthermore, methods of assessing and defining progressive keratoconus should be standardized. Trials with longer follow-up are required in order to assure that outcomes are measured after corneal wound-healing and stabilization of keratoconus. In addition, perioperative, intraoperative, and postoperative care should be standardized to permit meaningful comparisons of CXL methods. Methods to increase penetration of riboflavin through intact epithelium as well as delivery of increased dose of UVA may be needed to improve outcomes. PROs should be measured and reported. The visual significance of adverse outcomes, such as corneal haze, should be assessed and correlated with other outcomes, including PROs.

New perspectives in keratoconus treatment: an update on iontophoresis-assisted corneal collagen crosslinking

Keratoconus is a bilateral, asymmetric and progressive corneal disease. It usually results in apical thinning and steepening with corneal deformation and impaired vision. Since the early 1990 s, corneal collagen crosslinking (CXL) has remained the primary treatment to stabilize the progression of the disease. Iontophoresis-assisted CXL (I-CXL) has been proposed as a non-invasive alternative to standard epithelium-off technique, showing promising results. In this article, we review up to date literature to provide state of art knowledge and future perspectives of I-CXL.

Comparison of Standard and Transepithelial Corneal Cross-Linking for the Treatment of Keratoconus: A Meta-analysis

Purpose

To compare the clinical results of standard corneal cross-linking (SCXL) with transepithelial corneal cross-linking (TECXL) in progressive keratoconus using a meta-analysis.

Methods

PubMed, EMBASE, and Cochrane Central Register of Controlled Trials were searched up to June 2020 to identify relevant studies. The PRISMA guidelines were followed. Primary outcomes were change in uncorrected distance visual acuity and maximum keratometry (K_max) after CXL. Secondary outcomes were change in corrected distance visual acuity, mean refractive spherical equivalent (MRSE), spherical and cylindrical error, endothelial cells density (ECD), and central corneal thickness (CCT).

Results

Sixteen studies with a total of 690 eyes (SCXL: 332 eyes; TECXL: 358 eyes) were included. At the last follow-up, SCXL provided a greater decrease in maximum keratometry (K_max) than TECXL (weighted mean difference (WMD) −1.12; 95% confidence interval (CI) −1.96, −0.29). For the other outcomes, there were no statistically significant differences.

Conclusions

Except for a greater decrease in Kmax with SCXL group, both groups have a comparable effect on visual, pachymetric, and endothelial parameters at 24 months after surgery. Larger studies with a longer follow-up time are necessary to determine whether these techniques are comparable in the long term.

Iontophoretic Transepithelial Collagen Cross-Linking Versus Epithelium-Off Collagen Cross-Linking in Pediatric Patients: 3-Year Follow-Up

PURPOSE

To compare 3-year iontophoretic transepithelial corneal cross-linking (I-ON CXL) outcomes with epithelium-off collagen cross-linking (epi-off CXL) in pediatric patients.

METHODS

Forty eyes of 28 consecutive pediatric patients [mean age 14.3 ± 2.5 (SD) years; range, 9-18 years] with keratoconus were evaluated. Twenty eyes of 15 patients underwent I-ON and 20 eyes of 13 patients epi-off CXL. Mean corrected distance visual acuity, spherical equivalent, maximum keratometry (Kmax), posterior elevation of the thinnest point, and thickness of the thinnest point were evaluated. The Student t test was used to compare baseline and postoperative data. Keratoconus progression as a function of preoperative Kmax and cone location was evaluated.

RESULTS

At 36 months, corrected distance visual acuity statistically improved (from 0.18 ± 0.1 to 0.10 ± 0.1 logarithm of the minimum angle of resolution) in epi-off CXL, whereas spherical equivalent and posterior elevation of the thinnest point did not significantly change. Mean Kmax increased from the baseline +0.8 diopters (D) in epi-off and +2.9D in I-ON. In both groups, the thinnest point decreased. Keratoconus progression, defined by an increase of Kmax reading of the anterior corneal surface of at least 1.00D, occurred in 25% of epi-off and 50% of I-ON CXL over the 3-year period. Kmax value in I-ON, and cone location in both groups, seemed to be factors influencing the disease progression.

CONCLUSIONS

In pediatric patients, 3 years after treatment, epi-off CXL halted keratoconus progression in 75% of eyes, whereas I-ON CXL seemed to slow down keratoconus progression in 50% of eyes, mainly in those with highest Kmax and paracentral cone.

Current concepts in crosslinking thin corneas

Corneal cross-linking (CXL), introduced by Wollensak et al. in 2003, is a minimally invasive procedure to halt the progression of keratoconus. Conventional CXL is recommended in eyes with corneal thickness of at least 400 microns after de-epithelialization to prevent endothelial toxicity. However, most of the keratoconic corneas requiring CXL may not fulfill this preoperative inclusion criterion. Moderate-to-advanced cases are often found to have a pachymetry less than this threshold. There are various modifications to the conventional method to circumvent this issue of CXL thin corneas while avoiding the possible complications. This review is an update on the modifications of conventional CXL for thin corneas.

Two-year outcomes of a randomized controlled trial of transepithelial corneal crosslinking with iontophoresis for keratoconus

PURPOSE

To evaluate the 2-year clinical outcomes of corneal crosslinking (CXL) using transepithelial iontophoresis CXL (T-ionto CXL) in comparison with standard CXL for the treatment of progressive keratoconus.

SETTING

Single-site study.

DESIGN

Randomized controlled clinical trial with identifier code NCT02117999.

METHODS

The eyes of the participants were randomized to have either T-ionto CXL and/or standard CXL. Assessments of uncorrected (UDVA) and corrected (CDVA) distance visual acuities (logarithm of the minimum angle of resolution [logMAR]), manifest refraction spherical equivalent, maximum simulated keratometry (K) (diopters [D]), corneal higher-order aberrations (HOAs), central corneal thickness (CCT), and endothelial cell density (ECD) were performed at 3 days, 7 days, and 1, 3, 6, 12, and 24 months postoperatively.

RESULTS

The study comprised 34 eyes (25 patients). There were 22 eyes in the T-ionto CXL group and 12 eyes in the standard CXL group. Two years after T-ionto CXL and standard CXL, the mean maximum K flattened by -1.05 ± 1.20 D (P = .07) (20 eyes) and -1.51 ± .89 D (P < .001) (11 eyes), respectively. Two study cases (10%) and no control showed maximum K steepening of more than 1.0 D at 24 months postoperatively. The mean change in CDVA was -0.08 ± 0.15 logMAR (P = .04) and -0.02 ± 0.06 logMAR (P = .34) after T-ionto CXL and standard CXL, respectively. A significant average decrease in the myopic defocus (+0.81 D; P < .05) was found in both groups. No significant differences in the outcome measures between treatments were found at 24 months. The corneal HOAs, CCT, and ECD values did not change significantly in any group at 2 years postoperatively.

CONCLUSIONS

Clinically significant topographic, visual, and refractive improvements were found 2 years after T-ionto CXL; standard CXL showed more significant corneal apex flattening than the transepithelial iontophoresis protocol.

Trans-epithelial corneal collagen cross-linking with iontophoresis for progressive keratoconus

PURPOSE

To evaluate the efficacy of trans-epithelial corneal collagen cross-linking (CXL) with Iontophoresis among patients with progressive keratoconus.

METHODS

It is a prospective interventional study, which is based on 41 eyes of 23 patients, suffering from progressive keratoconus and treated with trans-epithelial corneal cross-linking, using iontophoresis with ETDA and trometamol-enriched riboflavin 5 phosphates 0.1% hypotonic solution (Ricrolin+, Soot Italia SpA, Italy).

RESULTS

The mean of uncorrected distance visual acuity and best corrected distant visual acuity was improved at 6 months with statistically significant differences from baseline (p < 0.05). There was no statistically significant difference in keratometric values, including K₁, K₂, K_m, topographic astigmatism, and central corneal thickness. Patients, who had completed 1 year (21 eyes of 12 patients) of the treatment, showed similar results.

CONCLUSION

The data indicated that corneal collagens cross-linking with iontophoresis using Ricroli+ may be an effective method in halting the progression of keratoconus without the side effects of epithelial removal, which may be encountered in the standard epi-off CXL procedure.

Efficacy of iontophoresis-assisted epithelium-on corneal cross-linking for keratoconus

Corneal cross-linking (CXL) is a noninvasive therapeutic procedure for keratoconus that is aimed at improving corneal biomechanical properties by induction of covalent cross-links between stromal proteins. It is accomplished by ultraviolet A (UVA) radiation of the cornea, which is first saturated with photosensitizing riboflavin. It has been shown that standard epithelium-off CXL (S-CXL) is efficacious, and it has been recommended as the standard of care procedure for keratoconus. However, epithelial removal leads to pain, transient vision loss, and a higher risk of corneal infection. To avoid these disadvantages, transepithelial CXL was developed. Recently, iontophoresis has been adopted to increase riboflavin penetration through the epithelium. Several clinical observations have demonstrated the safety and efficacy of iontophoresis-assisted epithelium-on CXL (I-CXL) for keratoconus. This review aimed to provide a comprehensive summary of the published studies regarding I-CXL and a comparison between I-CXL and S-CXL. All articles used in this review were mainly retrieved from the PubMed database. Original articles and reviews were selected if they were related to the I-CXL technique or related to the comparison between I-CXL and S-CXL.

Conventional and transepithelial corneal cross-linking for patients with keratoconus

Previous studies investigating the effectiveness of conventional corneal collagen cross-linking (CXL) and transepithelial CXL in keratoconus treatment have reported conflicting outcomes. Therefore, we conducted a meta-analysis to compare the effectiveness of these treatments. We searched MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials for prospective randomized controlled trials (RCTs) with no restrictions. We included visual acuity (corrected distance visual acuity, uncorrected distance visual acuity) and corneal keratometry (K) as primary outcome parameters, and spherical equivalent, central corneal thickness (CCT), and endothelial cell density, as secondary parameters. We finally included seven reports (including six RCTs involving 305 participants and 344 eyes). Our analysis revealed significant postoperative differences in average K and CCT values between conventional and transepithelial CXL-treated patients [K: weighted mean difference (WMD) = 0.79, 95% confidence interval (CI) = 0.04-1.53, p = 0.04; CCT: WMD = 4.53, 95% CI = 0.42-8.64, p = 0.03]. In contrast, we did not find any significant differences in visual acuity, flattest K value, steepest K value, cylinder K value, apex K value, spherical equivalent, or endothelial cell density between groups. In conclusion, transepithelial CXL has a more protective influence on corneal thickness than conventional CXL, and results in lesser postoperative corneal flattening. Further investigation of the clinical outcomes of transepithelial CXL is required.