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Ruojin Ren, Hongli Yang, Stuart Gardiner, Lin He, Juan Reynaud, Brad Fortune, Shaban Demirel, Claude Burgoyne; Global and Regional Discordance between Colocalized Heidelberg Retinal Tomograph (HRT) Rim Area and Spectral Domain Optical Coherence Tomography (SDOCT) Minimum Rim Measurements. Invest. Ophthalmol. Vis. Sci. 2013;54(15):85.
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To quantify global and regional neuroretinal rim area discordance between colocalized HRT Rim Area (RAHRT) and SDOCT minimum rim area (MRASDOCT) measurements in 190 glaucoma or high-risk ocular hypertension subjects.
Same day SDOCT (48 high-resolution, ONH centered, radial B-scans, Spectralis, 870nm, Heidelberg Engineering) and HRT (Heidelberg Engineering) images from one eye of each patient were colocalized using the HRT and SDOCT fundus reflectance images. For each SDOCT data set, Bruch’s membrane opening (BMO) and the internal limiting membrane (ILM) were hand delineated within every other SDOCT radial B-scan (n=24) allowing MRASDOCT, BMO centroid and the Fovea - BMO centroid (FoBMO) axis to be determined. RAHRT was based on a glaucoma specialist’s determination of the clinical disc margin and a 320 μm reference plane. Colocalized HRT and SDOCT data were divided into 12 common FoBMO-based segments (Figure 1) and the magnitude of global and sectoral RAHRT vs MRASDOCT discordance among all 190 eyes was assessed.
While global RAHRT was significantly larger than MRASDOCT (P < 0.001, Wilcoxon signed- rank test) there was wide discordance (Figure 2). Regionally, while RAHRT was significantly larger than MRASDOCT in the temporal inferior, temporal superior, superior temporal, superior, superior nasal and nasal superior sectors (all P < 0.001, Wilcoxon signed- rank test), there was no significant difference in the inferonasal quadrant (Figure 2). Sectoral RAHRT vs MRASDOCT discordance was substantial and similarly variable among all sectors.
SDOCT/HRT colocalization and a common, FoBMO regionalization strategy has allowed a precise comparison between HRT rim and SDOCT minimum rim assessments. HRT overestimates neuroretinal rim area compared to SDOCT especially in the superior and temporal quadrants. This discordance is substantial and varies across individual eyes, but its average magnitude is similar for all sectors. The clinical importance of this discordance is under study.
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