Measurement of the Hypotenuse of the Vertical Optic Nerve Head Cup with SD-OCT as a Diagnostic Biomarker for Glaucoma.

Abstract

Purpose : This study aims to evaluate the hypotenuse of the vertical optic nerve head cup (HVOC) and its association with structural and functional parameters in glaucomatous eyes and controls.

Methods : Subjects with glaucoma and controls underwent 24-2 perimetry and OCT. A vertical B-scan of the ONH with the largest cup extension was used for the measurements. The HVOC was calculated using the sides of a right triangle formed by the length and depth of the optic nerve cup. The length was measured as the distance between the innermost portion of the descending RNFL tissue at the Bruch’s membrane opening level. The depth was measured as the mean of the distances between the former line and the maximum and minimum depth of the superior, central and inferior portions of the anterior prelaminar tissue and the anterior limit of the lamina cribrosa (Figure 1). The circumpapillary retinal nerve fiber layer (cRNFL) and ganglion cell layer/inner plexiform layer (GCIPL) were analyzed using the average of the sectors from the ETDRS grid circles. Statistical analysis was performed using generalized estimating equations to allow for clustered observations. Age, gender, presence of glaucoma and disc area were accounted in the model. The area under the receiver operating characteristics curve (AUROC) for HVOC was also calculated.

Results : 109 eyes (67 subjects) were included, 95 in the glaucoma group and 14 in the control. The mean age was 66.13±12.38. The mean HVOC at the pre-laminar level (PL-HVOC) was 1298.80±291.99µm and 758.58±300.70µm for glaucoma and normal eyes, respectively, whereas the HVOC at the lamina cribrosa level (LC-HVOC) was 1341.15±290.22µm and 791.43±286.53µm, respectively. Both HVOC measurements were significantly associated with the cRNFL, GCIPL, mean deviation and visual field index, with a negative correlation (Table 1). Age and gender weren’t significant in any of the models. The AUROC for the PL-HVOC and LC-HVOC was 0.901 and 0.907, respectively (P<0.001).

Conclusions : The HVOC was significantly associated with structural and functional glaucoma parameters both at the pre-laminar and at the laminar levels. It differentiated well between normal and glaucomatous eyes. This parameter may constitute an additional ONH biomarker for the structural diagnosis and monitoring of glaucoma.

This is a 2020 Imaging in the Eye Conference abstract.

 

Measurement of the HVOC

 

Association between HVOC and Visual Field, cRNFL and GCIPL.