title: Bayesian machine learning classifiers for combining structural and functional measurements to classify healthy and glaucomatous eyes.
abstract: OBJECTIVE
  To determine whether combining structural (optical coherence tomography, OCT) and functional (standard automated perimetry, SAP) measurements as input for machine learning classifiers (MLCs; relevance vector machine, RVM; and subspace mixture of Gaussians, SSMoG) improves diagnostic accuracy for detecting glaucomatous eyes compared with using each measurement method alone.
  
  
  METHODS
  Sixty-nine eyes of 69 healthy control subjects (average age, 62.0, SD 9.7 years; visual field mean deviation [MD], -0.70, SD 1.41 dB) and 156 eyes of 156 patients with glaucoma (average age, 66.4, SD 10.2 years; visual field MD, -3.12, SD 3.43 dB) were imaged with OCT (Stratus OCT, Carl Zeiss Meditec, Inc., Dublin, CA) and tested with SAP (Humphrey Field Analyzer II with Swedish Interactive Thresholding Algorithm, SITA; Carl Zeiss Meditec, Inc.) within 3 months of each other. RVM and SSMoG MLCs were trained and tested on OCT-determined RNFL thickness measurements from 32 sectors ( approximately 11.25 degrees each) obtained in the circumpapillary area under the instrument-defined measurement ellipse and SAP pattern deviation values from 52 points from the 24-2 grid, independently and in combination. Tenfold cross-validation was used to train and test classifiers on unique subsets of the full 225-eye data set, and areas under the receiver operating characteristic curve (AUROC) for the classification of eyes in the test set were generated. AUROC results from classifiers trained on OCT and SAP alone and those trained on OCT and SAP in combination were compared. In addition, these results were compared to currently available OCT measurements (mean retinal nerve fiber layer [RNFL] thickness, inferior RNFL thickness, and superior RNFL thickness) and SAP indices (MD and pattern standard deviation [PSD]).
  
  
  RESULTS
  The AUROCs for RVM trained on OCT parameters alone, SAP parameters alone and OCT and SAP parameters combined were 0.809, 0.815, and 0.845, respectively. The AUROCs for SSMoG trained on OCT parameters alone, SAP parameters alone, and OCT and SAP parameters combined were 0.817, 0.841, and 0.869, respectively. Combining techniques using both RVM and SSMoG significantly improved on MLC analysis of OCT, but not SAP, measurements alone. Classification performance using RVM and SSMoG was statistically similar.
  
  
  CONCLUSIONS
  RVM and SSMoG Bayesian MLCs trained on OCT and SAP data can successfully discriminate between healthy and early glaucomatous eyes. Combining OCT and SAP measurements using RVM and SSMoG increased diagnostic performance marginally compared with MLC analysis of data obtained using each technology alone.
authors.affiliation: Hamilton Glaucoma Center, Department of Ophthalmology, University of California, San Diego, La Jolla, CA 92037-0946, USA. cbowd@eyecenter.ucsd.edu
authors.forename: Christopher
authors.initials: C
authors.lastname: Bowd
authors.forename: Jiucang
authors.initials: J
authors.lastname: Hao
authors.forename: Ivan M
authors.initials: IM
authors.lastname: Tavares
authors.forename: Felipe A
authors.initials: FA
authors.lastname: Medeiros
authors.forename: Linda M
authors.initials: LM
authors.lastname: Zangwill
authors.forename: Te-Won
authors.initials: TW
authors.lastname: Lee
authors.forename: Pamela A
authors.initials: PA
authors.lastname: Sample
authors.forename: Robert N
authors.initials: RN
authors.lastname: Weinreb
authors.forename: Michael H
authors.initials: MH
authors.lastname: Goldbaum
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001499:Bayes Theorem; D003430:Cross-Sectional Studies; D005902:Glaucoma, Open-Angle / Q000175:diagnosis*; D006801:Humans; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology; D009898:Optic Disk / Q000473:pathology; D009901:Optic Nerve Diseases / Q000175:diagnosis*; D012372:ROC Curve; D012165:Retinal Ganglion Cells / Q000473:pathology; D041623:Tomography, Optical Coherence; D014065:Tonometry, Ocular; D014786:Vision Disorders / Q000175:diagnosis*; D058609:Visual Field Tests; D014794:Visual Fields