Optic nerve head prelaminar tissue schisis: a sign of glaucomatous deformation?

Abstract

Purpose : We recently described¹ optical coherence tomography (OCT) scans of glaucomatous eyes that appear to represent splitting within the prelaminar tissues of the optic nerve head (ONH, e.g., Fig.1). The purpose of this study was to compare the frequency of observing ONH schisis in glaucomatous eyes (GL) versus healthy control eyes and to characterize the relationship between ONH schisis and glaucoma severity.

Methods : We included 298 eyes of 150 patients with a diagnosis of glaucoma or glaucoma suspect and 88 control eyes of 44 healthy volunteers. OCT scans were obtained using the SPECTRALIS (Heidelberg Engineering GmbH) Glaucoma Module Premium Edition with the Anatomic Positioning System, which records 24 radial B-scans centered on the ONH (Bruch’s membrane opening). Two reviewers masked to all other clinical, demographic and ocular information, rated the OCT scans of each eye for the presence of ONH schisis on a 4-point scale: 0 (none) to 3 (severe). Presence of schisis was defined as an average grade ≥2. The probability of ONH schisis was compared between study groups and against demographic and ocular factors, including function (visual field mean deviation, MD and pattern standard deviation, PSD) and structure (circumpapillary retinal nerve fiber layer thickness, RNFLT, ONH minimum rim width (MRW), mean and max cup depth).

Results : The probability of observing ONH schisis was greater in glaucomatous eyes (16.8%) compared to healthy control eyes (6.8%, p=0.023, logistic regression, Fig.2A). ONH schisis was more likely to be observed in eyes with thinner MRW, deeper cup (larger mean and max cup depth) and eyes of older individuals (Fig.2A). Severe ONH schisis in GL was typically accompanied by nasalization of the vasculature. Among GL individuals with any ONH schisis, it was present bilaterally in 32%; none of the healthy controls had bilateral ONH schisis.

Conclusions : ONH schisis may be a sign of glaucomatous deformation and reflect ongoing pathophysiological damage. It is observed by OCT more frequently in eyes with a diagnosis of glaucoma or glaucoma suspect, in eyes with thinner ONH rim tissue (MRW) and in eyes with deeper optic cups, including some with normal visual fields and RNFL thickness. ONH schisis can impact OCT image segmentation and diagnostic parameters, resulting in substantial overestimation of the true rim tissue thickness and underestimation of cup depth (e.g., Fig.2B).

¹Fortune B. IOVS 2019.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.