Definitions for Keratoconus Progression and Their Impact on Clinical Practice

Purpose: There is currently no consensus on which keratoconus need cross-linking nor on how to establish progression. This study assessed the performance of diverse progression criteria and compared them with our clinical knowledge of keratoconus evolution.Methods: This was a retrospective, longitudinal, observational study. Habitual progression criteria, based on (combinations of) keratometry (K-MAX ), front astigmatism (A(F)), pachymetry (P-MIN ), or ABCD progression display, from 906 keratoconus patients were analyzed. For each criterion and cutoff, we calculated %eyes flagged progressive at some point (R-PROG), individual consistency C-IND (%examinations after progression detection still considered progressive), and population consistency C POP (% eyes with C-IND >66%). Finally, other monotonic and consistent variables, such as front steep keratometry (K-2F), mean radius of the back surface (R-mB), and the like, were evaluated for the overall sample and subgroups.Results: Using a single criterion (e.g., triangle K-MAX >1D) led to high values of R-PROG. When combining two, (K-MAX and A F ) led to worse C POP and higher variability than (K-MAX and P-MIN); alternative criteria such as (K-2F and R-mB) obtained the best C POP and the lowest variability ( P <0.0001). ABC, as defined by its authors, obtained R-PROG of 74.2%. Using wider 95% confidence intervals (95% CIs) and requiring two parameters over 95CI reduced R-PROG to 27.9%.Conclusion: Previous clinical studies suggest that 20% to 30% of keratoconus cases are progressive. This clinical R-PROG value should be considered when defining KC progression to avoid overtreatment. Using combinations of variables or wider margins for ABC brings R PROG closer to these clinical observations while obtaining better population consistency than current definitions.