Establishing a precision reference benchmark for corneal epithelial aberration measurements using a new hybrid device across keratoconus stages.

Background: To establish a precision reference benchmark for corneal epithelial aberration measurements across different stages of keratoconus (KC) by evaluating the precision of a new spectral-domain optical coherence tomography-Placido disk device (MS-39; CSO).

Methods: Eyes with KC were classified into forme fruste keratoconus (FFKC), mild, moderate, and severe disease stage. Three consecutive corneal epithelial aberration measurements were obtained with the MS-39 by two skilled operators. The intraobserver repeatability and interobserver reproducibility were evaluated using within-subject standard deviation (S_w), test-retest variability (TRT), and intraclass correlation coefficient (ICC).

Results: The prospective study enrolled 141 eyes from 141 KC subjects. Subgroups included 32 eyes with FFKC, 29 with mild, 45 with moderate, and 35 with severe KC. In the FFKC, mild, moderate, and total groups, S_w and TRT for intraobserver repeatability were ≤ 0.18 μm and ≤ 0.50 μm, respectively. ICCs were ≥ 0.884 for most parameters except trefoil and astigmatism II. The S_w and TRT for interobserver reproducibility were ≤ 0.15 μm and ≤ 0.41 μm, respectively. ICCs were ≥ 0.917 except for trefoil and astigmatism II. In the severe group, the ICCs for intraobserver repeatability and interobserver reproducibility were 0.366 to 0.904 and 0.493 to 0.908.

Conclusions: The new MS-39 device demonstrated moderate-to-good precision in corneal epithelial aberration measurements for FFKC, mild, moderate and total KC. Despite the decrease associated with increasing KC severity, the potential of the device for early diagnosis and monitoring was still evident. The instrument's precision should be tailored to disease severity. Stage-specific TRT thresholds for epithelial aberration measurements were proposed for KC management.