Optic Disc Tilt Direction Determines the Location of Initial Glaucomatous Damage

PURPOSE. To explore differences in optic disc tilt and torsion between normal control and glaucoma subjects, and to determine whether the direction of optic disc tilt is consistent with the initial location of glaucomatous visual field (VF) defect. METHODS. Glaucoma patients with isolated superior or inferior hemifield loss (n = 136) and normal controls (n = 99) were analyzed. Disc ovality index and torsion degree were measured on retinal photographs. Imaging of optic disc was obtained using Heidelberg retinal tomography (HRT) III and Cirrus spectral-domain optical coherence tomography (OCT). The degree of temporal disc tilt was assessed using horizontal topographic images and vertical (upward or downward) disc tilt using vertical topographic images, respectively. RESULTS. In all subjects, disc ovality was significantly associated with HRT- and OCT-measured temporal disc tilt and axial length (AL) (all P < 0.001), whereas disc torsion degree was associated with HRT-and OCT-measured vertical disc tilt and AL (all P < 0.05). Association of AL with disc ovality and torsion became more evident as the mean deviation increased. When data on glaucoma patients with superior and inferior hemifield defects were compared, the vertical disc tilt (HRT-and OCT-assessed, P < 0.001 and 0.030, respectively) and the torsion degree (P = 0.002) differed significantly. Upon multivariate logistic regression analysis, the HRT-measured vertical disc tilt was an independent factor determining initial location of the VF defect (P = 0.012). CONCLUSIONS. Measurement of vertical disc tilt may give valuable information about the superior versus inferior regional susceptibilities of glaucoma.