Association of Visual Field, Cup-Disc Ratio, and Magnetic Resonance Imaging of Optic Chiasm

Objective: To assess the association of visual field, vertical cup-disc (VC/D) ratio, and vertical height of optic chiasm. Design: Case series. Setting: Outpatient eye clinic. Patients: Eighteen patients with low, normal, or elevated intraocular pressure, with or without visual field defects. Intervention: Measurement of visual field, VC/D ratio, and vertical height of optic chiasm. Main Outcome Measures: Association between VC/D ratio and visual field defects compared with association between vertical height of optic chiasm and visual field defects. Results: Visual field defects were graded as 0, 1 to 10, and 11 to 20 (from least to most severe). Group mean VC/D ratios were 0.47 (0), 0.55 (1-10), and 0.69 (11-20) for right eyes and 0.48(0), 0.57 (1-10), and 0.75 (11-20) for left eyes. The significance level for trend was P =.02 for right eyes and P =.006 for left eyes. Group mean chiasm heights were 3.5 (0), 2.9 (1-10), and 2.2 (11-20) mm for right eyes and 3.5 (0), 2.8 (1-10), and 2.2 (11-20) mm for left eyes. The significance level for trend was P P =.002 for left eyes. To assess the simultaneous effects of VC/D ratio and chiasm height on the visual field defects groups, we used ordinal logistic regression models. Models with both variables implied that chiasm height was a stronger predictor of visual field defects group than VC/D ratio (for right eyes, P =.04 [VC/D ratio], P =.001 [chiasm height]; for left eyes, P =.11 [VC/D ratio], P =.005 [chiasm height]). Conclusions: When chiasm and VC/D ratio were analyzed in the same model, chiasm height was a stronger predictor of visual field defects. In advanced visual field defects, the optic chiasm is atrophic.