Measurement of the hypotenuse of the vertical optic nerve head cup with spectral-domain optical coherence tomography for the structural diagnosis of glaucoma

Purpose: To evaluate the hypotenuse of the vertical optic nerve head cup (HVOC), measured using the length and depth of the cup obtained with enhanced depth imaging spectral-domain optic coherence tomography (SD-OCT), as a biomarker for glaucoma diagnosis. Methods: This was a prospective cross-sectional study of patients with glaucoma and controls. SD-OCT was performed in all participants to assess average circumpapillary retinal nerve fiber layer (RNFL) thickness. A vertical B-scan of the optic nerve head (ONH) was obtained for HVOC measurement. The length and depth of the optic nerve cup formed the sides of a right triangle that were used to calculate the HVOC. Participants also underwent standard automated perimetry. Results: One hundred and fifty-six eyes were divided into three groups: mean deviation (MD) <-7 dB (60 eyes); MD ≥-7 dB (74 eyes); and healthy subjects (22 eyes). The mean (SD) HVOC in these groups was 1,419.8 (347.2) µm, 1,234.6 (258.8) µm, and 685.79 (315.4) µm (P<0.01), respectively. In the secondary structure-function analysis, only discs with a vertical diameter of 1.51-2.00 mm were included (120 eyes). The HVOCs were divided into four percentile groups, with the following means: 940, 1,128, 1,390, and 1,662 µm. There was a significant difference in MD between percentile groups 1 and 3 (P<0.03), 1 and 4 (P<0.001), 2 and 3 (P<0.02), and 2 and 4 (P<0.001). RNFL thickness differed among all percentile groups (P<0.001). Conclusion: HVOC may provide an additional morphometric biomarker for the structural evaluation of ONH remodeling in glaucoma.