Influence of automated disc margin determination on Stratus OCT optic nerve head measurements

Abstract

André Soares de Camargo, Luiz Alberto Soares Melo Jr, Flavio Eduardo Hirai, Ivan Maynart Tavares Glaucoma Service, Department of Ophthalmology and Visual Sciences, Federal University of São Paulo, Paulista Medical School, São Paulo, Brazil Purpose: To analyze the influence of manual correction of the automatically determined edge of the optic nerve head (ONH) in optic disc measurements in cases in which the optical coherence tomography did not identify the disc limits correctly. Methods: The study included 127 eyes from 127 consecutive patients with glaucoma, suspects, and healthy individuals. In a retrospective analysis, eyes that underwent testing with the Stratus OCT (software version 4.0, Carl Zeiss Meditec, Dublin, CA, USA) Fast Optic Disc protocol were evaluated. Forty-seven eyes in which either the manual assignment was not necessary or the signal strength was below six were excluded. After image acquisition and processing, one expert examiner manually corrected the determination of the edge of the ONH, identified as the end of the retinal pigment epithelium/choriocapillaris complex. Disc area, cup area, rim area, and cup/disc area ratio results were compared before and after the optic disc margin manually corrected determination. Paired t-test was performed to evaluate the differences, and Bland–Altman plots were used to display the relationships between measurements. Results: Eighty eyes from 80 individuals were included in the analyses. No statistically significant difference (P=0.538) was found when analyzing results obtained with automated and manual determination of rim area (mean ± standard deviation; 1.30±0.45 mm2 and 1.29±0.39 mm2, respectively). Cup area (1.39±0.58 mm2 and 1.31±0.55 mm2, respectively), cup/disc area ratio (0.50±0.16 mm2 and 0.49±0.15 mm2, respectively), and disc area results (2.69±0.55 mm2 and 2.60±0.51 mm2, respectively) were significantly different. Conclusion: The Stratus OCT ONH Report results were little influenced when optic disc limits were manually determined. Therefore the standard automated Stratus OCT disc margin assignment is adequate, and manual correction is not necessary. Keywords: optical coherence tomography, optic nerve head, glaucoma, diagnosis