Optic Disc Characteristics in Patients With Glaucoma and Combined Superior and Inferior Retinal Nerve Fiber Layer Defects

IMPORTANCE Eyes with initial bihemifield defects show faster progression compared with eyes with initial single-hemifield involvement, suggesting greater optic nerve susceptibility to glaucomatous damage. We hypothesized that certain disc phenotypes may exist in patients with glaucoma who have bihemispheric structural damage at the initial stage of the disease. OBJECTIVE To identify the optic disc characteristics related to bihemispheric retinal nerve fiber layer (RNFL) defects in early-stage glaucoma. DESIGN, SETTING, AND PARTICIPANTS A cross-sectional study of 136 patients with early-stage primary open-angle glaucoma from a glaucoma referral practice. Eyes were divided into those with RNFL defects in the superior or the inferior hemisphere (group 1) and those with bihemispheric RNFL defects (group 2). We measured the degree of horizontal tilt angle and RNFL thickness using spectral-domain optical coherence tomography. We performed multivariate logistic regression analysis to determine potential risk factors related to the bihemispheric RNFL defects. EXPOSURES Bihemispheric RNFL defects. MAIN OUTCOMES AND MEASURES Disc ovality (defined as the ratio between the longest and shortest diameters of the optic disc), the degree of horizontal tilt angle, and the presence of bihemispheric RNFL defects. Asymmetry in RNFL thickness between hemispheres was defined as the difference between the superior and inferior mean RNFL thickness. RESULTS Disc ovality (mean [SD], 1.09 [0.12] in group 1 vs 1.18 [0.18] in group 2; difference, -0.09; 95% Cl, -0.14 to -0.03), proportion of tilted discs (5.3% vs 17.5%, respectively; difference, -12.2; 95% Cl, -13.0 to -11.4), and horizontal tilt angle (mean [SD], 4.17 degrees [4.13 degrees] vs 5.93 [4.84], respectively; difference, -1.76; 95% Cl, -3.47 to -0.03) were significantly different between groups land 2 (P = .001, P = .03, and P = .045, respectively). The asymmetry in RN FL thickness decreased with increased disc ovality (exponentiation of the B coefficient, 1.67; 95% CI, 1.10-2.55; P = .02), although associations were not identified with spherical equivalent, axial length, or the angle between the temporal retinal veins. In multivariate logistic analysis, disc ovality was suggested to be an independent risk factor for bihemispheric RNFL defects, after controlling for mean deviation, age, axial length, and disc area (P = .02). CONCLUSIONS AND RELEVANCE Optic disc tilt appears to be associated with bihemispheric RN FL defects in patients with early glaucoma, regardless of their refractive status. These data suggest that disc tilt, associated with bihemispheric structural damages, is a risk factor for glaucoma progression.