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Published on: November 12, 2015
New keratoconus grading system based on OCT: threshold adjustment for SS-OCT
Nan-Ji Lu1, Frederik Raiskup, Lutz E Pillunat
1From the Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China (Lu); Department of Ophthalmology, University Hospital Carl Gustav Carus, TU Dresden, Dresden, Germany (Raiskup, Pillunat, Herber); National Clinical Research Center for Ocular Diseases, Eye Hospital, Wenzhou Medical University, Wenzhou, China (Wang, Cui); State Key Laboratory of Ophthalmology, Optometry and Visual Science, Eye Hospital, Wenzhou Medical University, Wenzhou, China (Wang, Cui).
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.
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