title: Measurement of the optic disc vertical tilt angle with spectral-domain optical coherence tomography and influencing factors.
abstract: OBJECTIVE
  To report a novel method for measuring the vertical tilt angle of the optic nerve (ON) head and to investigate the associated factors.
  
  
  METHODS
  Cross-sectional diagnostic study.
  
  
  METHODS
  One hundred and twelve normal, glaucomatous, and glaucoma suspect eyes (99 patients) were enrolled in this study. Subjects underwent a full eye examination, biometry, and spectral-domain optical coherence tomography (SDOCT). The vertical tilt angle was measured on high-resolution cross-sectional SDOCT images passing through the ON head and foveal centers using the inner edges of the Bruch membrane opening as the reference plane. The correlation between the vertical tilt angle with the ovality index and the potential associated factors was estimated with univariate and multivariate linear regression analyses.
  
  
  RESULTS
  The median (interquartile range, [IQR]) axial length and visual field mean deviation were 24.5 (23.8-25.3) mm and -0.9 (-2.76 to 0.26) dB. The median (IQR) tilt angle was 3.5 (1.2-11.2) degrees. There was a moderate correlation between the ovality index and tilt angle (Spearman ρ = 0.351; P < .001). In univariate analyses, axial length, spherical equivalent, and mean deviation were correlated with the tilt angle (P = .002, P = .011, and P = .013, respectively). Axial length, mean deviation, and their interaction showed a statistically significant correlation with the tilt angle in multivariate analyses (P = .044 for axial length, P = .039 for mean deviation, and P = .028 for their interaction).
  
  
  CONCLUSIONS
  We describe a new method for measuring the ON head vertical tilt angle with high-resolution SDOCT imaging. The ovality index demonstrated only a moderate correlation with the tilt angle measurements and hence is not a good proxy measure for the vertical ON head tilt angle. Axial length and visual field mean deviation are the main factors associated with the ON head vertical tilt angle. The underlying basis for the relationship of vertical tilt angle and glaucoma severity should be further explored.
authors.affiliation: Glaucoma Division, Jules Stein Eye Institute, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.
authors.forename: Hamid
authors.initials: H
authors.lastname: Hosseini
authors.forename: Nariman
authors.initials: N
authors.lastname: Nassiri
authors.forename: Parham
authors.initials: P
authors.lastname: Azarbod
authors.forename: JoAnn
authors.initials: J
authors.lastname: Giaconi
authors.forename: Tom
authors.initials: T
authors.lastname: Chou
authors.forename: Joseph
authors.initials: J
authors.lastname: Caprioli
authors.forename: Kouros
authors.initials: K
authors.lastname: Nouri-Mahdavi
mesh_terms: D058452:Axial Length, Eye / Q000473:pathology; D001699:Biometry; D003430:Cross-Sectional Studies; D005260:Female; D005902:Glaucoma, Open-Angle / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009798:Ocular Hypertension / Q000175:diagnosis; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis*; D011446:Prospective Studies; D012307:Risk Factors; D041623:Tomography, Optical Coherence; D014794:Visual Fields