Lamina cribrosa pore analysis in glaucomatous human optic nerve heads in vivo

Abstract

Purpose: The aim of this study was to use a novel semi-automatic segmentation technique to analyse the pore parameters in optical coherence tomography (OCT) datasets of the human glaucomatous lamina cribrosa (LC).

Methods: Optic nerve heads (ONHs) of ten glaucoma and ten age-matched controls were imaged using a laboratory 1050nm spectral domain OCT device, operating at 47,000 a-scans/sec, with 5-7µm axial resolution. OCT volumes of 512x512 a-scans over a 18.7 degree field centred on the ONH were acquired. ONH OCT datasets were post-processed using ImageJ. Three different regions of interest (ROIs) were selected within each LC avoiding shadows cast by ONH vasculature. Semi-automatic segmentation was performed in ImageJ on 300x300 µm ROI within the LC to analyse pore orientation, aspect ratio, area, and count.

Results: Segmentation of individual pores within different regions of interest within the LC was achieved in at least one ROI in all ONHs. However vascular shadowing caused by the temporal arcades or cilioretinal artery prevented the location of the ROI in some subjects, notably in the superior region of control ONHs. Analysis of the anterior LC to a depth of 10µm revealed that pore areas ranged from 436-6853 µm² in the glaucoma group and 418-4542 µm² in the controls. Pores were significantly more oval (reflected by an increase in aspect ratio) in the inferior and superior regions of the ONH, when compared to centro-temporal region in the glaucoma group (p=0.011, Kruskal Wallis test). Pore count was lower in glaucoma subjects, compared to age-matched controls.

Conclusions: Our preliminary findings indicate that changes in LC pores parameters in the glaucomatous ONHs can be detected using OCT at 1050nm. Further improvements in segmentation methodology and ROI selection will increase the area of ONH available for analysis and improve the accuracy of this technique. Ultimately, this will provide us with an opportunity to analyse the LC in vivo, for the detection of changes and monitoring progression in glaucomatous optic neuropathy. In addition, this is likely to be an invaluable tool in assessing the effects of therapeutic interventions on the ONH.

Keywords: 577 lamina cribrosa • 519 extracellular matrix • 550 imaging/image analysis: clinical