title: Agreement between automated and manual quantification of corneal nerve fiber length: Implications for diabetic neuropathy research.
abstract: OBJECTIVE
  Quantification of corneal nerve fiber length (CNFL) by in vivo corneal confocal microscopy represents a promising diabetic neuropathy biomarker, but applicability is limited by resource-intensive image analysis. We aimed to evaluate, in cross-sectional analysis of non-diabetic controls and patients with type 1 and type 2 diabetes with and without neuropathy, the agreement between manual and automated analysis protocols.
  
  
  METHODS
  Sixty-eight controls, 139 type 1 diabetes, and 249 type 2 diabetes participants underwent CNFL measurement (N=456). Neuropathy status was determined by clinical and electrophysiological criteria. CNFL was determined by manual (CNFLManual, reference standard) and automated (CNFLAuto) protocols, and results were compared for correlation and agreement using Spearman coefficients and the method of Bland and Altman (CNFLManualsubtracted from CNFLAuto).
  
  
  RESULTS
  Participants demonstrated broad variability in clinical characteristics associated with neuropathy. The mean age, diabetes duration, and HbA1c were 53±18years, 15.9±12.6years, and 7.4±1.7%, respectively, and 218 (56%) individuals with diabetes had neuropathy. Mean CNFLManualwas 15.1±4.9mm/mm2, and mean CNFLAutowas 10.5±3.7mm/mm2(CNFLAutounderestimation bias, -4.6±2.6mm/mm2corresponding to -29±17%). Percent bias was similar across non-diabetic controls (-33±12%), type 1 (-30±20%), and type 2 diabetes (-28±16%) subgroups (ANOVA, p=0.068), and similarly in diabetes participants with and without neuropathy. Levels of CNFLAutoand CNFLManualwere both inversely associated with neuropathy status.
  
  
  CONCLUSIONS
  Although CNFLAutosubstantially underestimated CNFLManual, its bias was non-differential between diverse patient groups and its relationship with neuropathy status was preserved. Determination of diagnostic thresholds specific to CNFLAutoshould be pursued in diagnostic studies of diabetic neuropathy.
authors.affiliation: Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Scarr
authors.affiliation: Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Leif E
authors.initials: LE
authors.lastname: Lovblom
authors.affiliation: Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Ilia
authors.initials: I
authors.lastname: Ostrovski
authors.affiliation: Division of Endocrinology and Metabolism, Department of Medicine, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Dylan
authors.initials: D
authors.lastname: Kelly
authors.affiliation: Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Tong
authors.initials: T
authors.lastname: Wu
authors.affiliation: Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Mohammed A
authors.initials: MA
authors.lastname: Farooqi
authors.affiliation: Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Elise M
authors.initials: EM
authors.lastname: Halpern
authors.affiliation: The Ellen and Martin Prosserman Centre for Neuromuscular Diseases, Krembil Neuroscience Centre, Division of Neurology, Department of Medicine, University Health Network, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Mylan
authors.initials: M
authors.lastname: Ngo
authors.affiliation: The Ellen and Martin Prosserman Centre for Neuromuscular Diseases, Krembil Neuroscience Centre, Division of Neurology, Department of Medicine, University Health Network, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Ng
authors.affiliation: Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Andrej
authors.initials: A
authors.lastname: Orszag
authors.affiliation: The Ellen and Martin Prosserman Centre for Neuromuscular Diseases, Krembil Neuroscience Centre, Division of Neurology, Department of Medicine, University Health Network, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Vera
authors.initials: V
authors.lastname: Bril
authors.affiliation: Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada; Division of Endocrinology and Metabolism, Department of Medicine, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada. Electronic address: bperkins@mtsinai.on.ca.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Perkins
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D003315:Cornea / Q000294:innervation* / Q000473:pathology*; D003430:Cross-Sectional Studies; D003922:Diabetes Mellitus, Type 1 / Q000150:complications / Q000175:diagnosis / Q000473:pathology; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000175:diagnosis / Q000473:pathology; D003929:Diabetic Neuropathies / Q000175:diagnosis* / Q000473:pathology; D003930:Diabetic Retinopathy / Q000175:diagnosis / Q000473:pathology; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D018613:Microscopy, Confocal; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology*; D010363:Pattern Recognition, Automated / Q000379:methods; D010808:Physical Examination / Q000379:methods
keywords: Biomarkers; Corneal confocal microscopy; Corneal nerve fiber length; Diabetes; Diabetic neuropathy; Neuropathy