Effect of apical clearance rigid corneal contact lens fitting on keratoconus progression: a controlled longitudinal analysis

Purpose: To evaluate the impact of apical clearance rigid corneal contact lens (RCCL) fitting on keratoconus (KC) progression compared to untreated KC patients over a 12-month period. Methods: This retrospective, controlled longitudinal study included 237 eyes with KC from two centers between 2018 and 2023. Following propensity score matching for baseline age and maximum keratometry (K_max), 31 eyes each were assigned to untreated and RCCL groups. RCCLs were fitted using the apical clearance method. Assessments at baseline, 3, 6, and 12 months included best-corrected visual acuity (BCVA), Scheimpflug corneal tomography and higher-order aberrations (HOAs). KC progression was defined by any of the following: an increase in K_max or anterior steep keratometry (K2) of >1.0 D, a decrease in thinnest corneal thickness (TCT) of > 10 μm, or a loss of >1 line of BCVA. Longitudinal changes were analyzed using generalized estimating equations (GEE). Results: No significant differences in BCVA, tomographic indices, or HOAs were observed between the untreated and RCCL groups at baseline or during follow-up at 3 and 12 months (all p > 0.05). KC progression rates were comparable between the groups, occurring in 12.9 % of untreated eyes and 19.35 % of RCCL treated eyes by 12 months (p = 0.731). GEE analysis revealed a significant reduction in K2 at 3 months within the RCCL group (p = 0.003); however, no other significant longitudinal differences were detected within or between groups at any follow–up period. Conclusion: Apical clearance RCCL fitting did not significantly affect overall KC progression compared with no treatment over 12 months. However, the significant reduction in K2 at 3 months in the RCCL group suggests that one week of contact lens discontinuation may not be sufficient for the cornea to fully return to its natural state.