title: From clinical examination of the optic disc to clinical assessment of the optic nerve head: a paradigm change.
abstract: OBJECTIVE
  To review and interpret the anatomy of the optic nerve head (ONH) detected with spectral-domain optical coherence tomography (SD OCT) pertaining to the clinical examination of the optic disc and to propose that a paradigm change for clinical assessment of the ONH is necessary.
  
  
  METHODS
  Perspective.
  
  
  METHODS
  Presently, the clinician evaluates neuroretinal rim health according to the appearance of the optic disc, the clinically visible surface of the ONH. Recent anatomic findings with SD OCT have challenged the basis and accuracy of current rim evaluation. We demonstrate why incorporation of SD OCT imaging of the ONH into the clinical examination of the disc is required.
  
  
  RESULTS
  Disc margin-based rim evaluation lacks a solid anatomic basis and results in variably inaccurate measurements for 2 reasons. First, the clinically visible disc margin is an unreliable outer border of rim tissue because of clinically and photographically invisible extensions of Bruch's membrane. Second, rim tissue orientation is not considered in width measurements. We propose alternative anatomically and geometrically accurate SD OCT-based approaches for rim assessment that have enhanced detection of glaucoma. We also argue for new data acquisition and analysis strategies with SD OCT that account for the large interindividual variability in the angle between the fovea and ONH.
  
  
  CONCLUSIONS
  We propose a 4-point paradigm change for clinical assessment of the ONH that is anchored to the eye-specific anatomy and geometry of the ONH and fovea. Our approach is designed to enhance the accuracy and consistency of rim width, as well as of peripapillary and macular intraretinal thickness measurements.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia, Canada. bal@dal.ca
authors.forename: Balwantray C
authors.initials: BC
authors.lastname: Chauhan
authors.forename: Claude F
authors.initials: CF
authors.lastname: Burgoyne
mesh_terms: D016570:Bruch Membrane / Q000033:anatomy & histology; D006801:Humans; D009412:Nerve Fibers; D009898:Optic Disk / Q000033:anatomy & histology*; D010781:Photography; D012165:Retinal Ganglion Cells / Q000166:cytology; D041623:Tomography, Optical Coherence / Q000379:methods*