title: Variation in optical coherence tomography signal quality as an indicator of retinal nerve fibre layer segmentation error.
abstract: OBJECTIVE
  Commercial optical coherence tomography (OCT) systems use global signal quality indices to quantify scan quality. Signal quality can vary throughout a scan, contributing to local retinal nerve fibre layer segmentation errors (SegE). The purpose of this study was to develop an automated method, using local scan quality, to predict SegE.
  
  
  METHODS
  Good-quality (global signal strength (SS) ≥ 6; manufacturer specification) peripapillary circular OCT scans (fast retinal nerve fibre layer scan protocol; Stratus OCT; Carl Zeiss Meditec, Dublin, California, USA) were obtained from 6 healthy, 19 glaucoma-suspect and 43 glaucoma subjects. Scans were grouped based on SegE. Quality index (QI) values were computed for each A-scan using software of our own design. Logistic mixed-effects regression modelling was applied to evaluate SS, global mean and SD of QI, and the probability of SegE.
  
  
  RESULTS
  The difference between local mean QI in SegE regions and No-SegE regions was -5.06 (95% CI -6.38 to 3.734) (p<0.001). Using global mean QI, QI SD and their interaction term resulted in the model of best fit (Akaike information criterion=191.8) for predicting SegE. Global mean QI ≥ 20 or SS ≥ 8 shows little chance for SegE. Once mean QI<20 or SS<8, the probability of SegE increases as QI SD increases.
  
  
  CONCLUSIONS
  When combined with a signal quality parameter, the variation of signal quality between A-scans provides significant information about the quality of an OCT scan and can be used as a predictor of segmentation error.
authors: UPMC Eye Center, Eye & Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.
authors: Lindsey S
authors: LS
authors: Folio
authors: Gadi
authors: G
authors: Wollstein
authors: Hiroshi
authors: H
authors: Ishikawa
authors: Richard A
authors: RA
authors: Bilonick
authors: Yun
authors: Y
authors: Ling
authors: Larry
authors: L
authors: Kagemann
authors: Robert J
authors: RJ
authors: Noecker
authors: James G
authors: JG
authors: Fujimoto
authors: Joel S
authors: JS
authors: Schuman
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005500:Follow-Up Studies; D005902:Glaucoma, Open-Angle / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D007089:Image Enhancement / Q000592:standards*; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology*; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D011446:Prospective Studies; D015203:Reproducibility of Results; D012165:Retinal Ganglion Cells / Q000473:pathology*; D041623:Tomography, Optical Coherence / Q000592:standards*; D014794:Visual Fields