Definition of Progressive Keratoconus: A Systematic Review.

Purpose: To identify the definitions used for progressive keratoconus in the literature.

Methods: A systematic literature review aimed to identify the definitions used for "progressive keratoconus" in the published articles. A comprehensive search from January 2018 to May 2023 was conducted across Cochrane Library, PubMed, Taylor & Francis, Web of Science, and other bibliographic databases at Oftalmosalud, Lima, Peru. The inclusion criteria were articles including patients with keratoconus without any previous surgical procedure and containing the definition of "progressive keratoconus" or "keratoconus progression" and a sample size greater than 10 eyes.

Results: A total of 221 articles were included for analysis. The 3 most frequent parameters to define progression included data from anterior curvature, pachymetry, and refraction used in 97.8% (216/221), 37.6% (83/221), and 32.1% (71/221) of the articles, respectively. Specifically, the most frequent criterion used was maximum keratometry (Kmax), used in 85.5% (189/221) of the articles. Progression was assessed between 6- and 12-month follow-up in 64.7% (143/221) of the articles. Data from posterior cornea were used in only 8.1% (18/221) of the studies. None of the studies included data from the corneal epithelium.

Conclusions: The present study demonstrates the lack of unified criteria to define progression of keratoconus and an underutilization of the technology described. It also shows that the single point Kmax measurement is the most commonly used criterion, followed by a change in refractive astigmatism and thinning at the thinnest pachymetric point.