New keratoconus grading system based on OCT: threshold adjustment for SS-OCT

Abstract

Purpose: To assess the performance of the STEP keratoconus (KC) grading system using swept-source optical coherence tomography (SS-OCT) and to compare the relative performance of SS-OCT and spectral-domain OCT (SD-OCT) for thickness measurements.

Setting: University hospitals in Germany and China.

Designs: Retrospective case-control study.

Methods: Rotating Scheimpflug tomography (RSC, Pentacam) and SS-OCT (ANTERION) were used to examine 152 normal and 314 KC eyes from a German cohort; the STEP system (stroma thinnest thickness [ST] and epithelium SD [EP]) was generated in SS-OCT and compared with RSC ABC system. Pentacam and SD-OCT (RTVue-XR) data from a Chinese cohort of 236 normal and 331 KC eyes were utilized to indirectly assess interdevice agreement between SS-OCT and SD-OCT using Bland-Altman plots and linear regression. Optimized thresholds for STEP "ST" were determined for SS-OCT.

Results: In normal eyes, STEP "ST" agreement with RSC "C" was 91.45%, dropping to 28.98% in KC eyes. STEP "EP" showed 58.55% and 60.53% agreement with RSC "A" and "B" in normal eyes and 36.62% and 52.87% in KC eyes, respectively. SS-OCT's ST values were estimated to be higher than those of SD-OCT (estimated mean difference = 23.18 and 20.91 μm in the normal and KC eyes, respectively). An adjusted threshold of STEP ST for SS-OCT was proposed.

Conclusions: SS-OCT's STEP EP aligned well with the RSC ABC system, whereas thresholds for SS-OCT's STEP ST required adjustment for more accurate clinical application. These findings highlight important considerations for thickness measurement discrepancies between SS-OCT and SD-OCT, with broader implications for future clinical practice and research.