Oxygen in Corneal Collagen Crosslinking to Treat Keratoconus: A Systematic Review and Meta-Analysis

Abstract

Purpose: Keratoconus is a disorder that results in visual loss from increased corneal high-order aberrations and irregular astigmatism and reduces quality of life. The primary treatment for progressive keratoconus is crosslinking (CXL). Recently, it has been suggested that oxygen enhances the type II photodynamic reaction of CXL that is oxygen dependent. Our study investigated the effect of increased oxygen availability in epithelium-on CXL on visual acuity and corneal curvature. Methods: We searched PubMed, EMBASE, Medline, Web of Science, and Scopus databases on November 3, 2021. We included studies that reported increased oxygen availability during CXL in patients with keratoconus published within the last 10 years. A meta-analysis on the primary outcomes, maximum keratometry, and corrected distance visual acuity, was conducted. Results: The search yielded 108 publications which were screened and assessed for eligibility. Six studies were included in the systematic review and 5 studies were included in our meta-analysis of the outcomes of increased oxygen availability in accelerated CXL. The meta-analysis on data after 6 months of follow-up found a significant decrease in mean maximum keratometry of 1.2 diopter (95% confidence interval: 0.2–2.3; P=0.02) and an improvement in mean corrected distance visual acuity by 0.08 logMAR (95% confidence interval, 0.02–0.13; P=0.01). There were no serious adverse events reported. Conclusions: Increasing oxygen during epithelium-on CXL improved visual acuity and produced corneal flattening without any serious adverse events in patients with keratoconus. The demarcation line depth was significantly higher with oxygen compared to the control group. Further data are required with a control group and long-term follow-up across a range of CXL protocols for implementation into standard clinical practice.

Update on corneal crosslinking for keratoconus and corneal ectasia

“…Early results of transepithelial crosslinking have been mixed. A recent meta-analysis comparing epi off and epi on CXL, including 27 studies comprising a total of 1622 eyes from 1399 patients with keratoconus, was performed [18]. The primary outcomes measured were changes in corrected distance visual acuity (CDVA) and maximum keratometry (Kmax), and the secondary outcomes included uncorrected distance visual acuity (UDVA), central corneal thickness (CCT), and adverse events.…”

Corneal collagen cross-linking in patients with keratoconus from the Dresden protocol to customized solutions: theoretical basis

“…Safety: Pulsed CXL The proposed clinical solution, to address these problems, is represented by the use of pulsed light: instead of administering the dosage of UV-A continuously, irradiation involves alternating phases on/off. These protocols have shown good efficacy and tolerability, at least as regards some parameters, mainly represented by the depth of the demarcation line (DL) and by the reduced toxicity [68][69][70] . The problem is that, even from a clinical point of view, the results collected are contradictory.…”