Reference planes for measuring of lamina cribrosa depth with optical coherence tomography

Abstract

Purpose : Anterior lamina cribrosa depth (LCD) is thought to be an important structural parameter of the optic nerve in glaucoma. However, there is no agreement on the optimal technique for its measurement. We performed a reproducibility study to compare two possible reference planes from which to measure LCD: Bruch’s membrane (BM) or choroid-sclera interface (CSI).

Methods : We included 16 glaucoma patients (mean[SD] age: 65.5[8.7] years) and 16 normal controls (mean[SD] age: 51.0[19.6] years). One randomly selected eye of each subject was examined with enhanced depth imaging spectral-domain optical coherence tomography (EDI-OCT, Spectralis, Heidelberg Engineering) 3 times on the same day. The EDI-OCT scan pattern consisted of 24 angularly equidistant radial B-scans centered on Bruch’s membrane opening (BMO). In each scan we manually segmented the inner limiting membrane, BM, CSI and the anterior laminar surface. Two independent reference planes were generated, one based on the BM and other based on the CSI, according to their position at a ring centered on the BMO, with inner radius of 1700 µm and outer radius of 1800 µm. From each reference plane, the LCD was measured at all visible locations and combined into a surface, to compute the average LCD and visible laminar area (Figure 1). The optic nerve head neuroretinal rim was quantified by the global BMO-minimum rim width (BMO-MRW). Reproducibility of measurements was assessed by within-subject standard deviations. Factors related to the measurements reproducibility were assessed with Spearman correlation coefficients.

Results : The mean (SD) LCD measured with the BM and CSI reference planes was 485 (124) µm and 344 (112) µm, respectively. The respective within-subject standard deviation of LCD was 7.0 µm (95% CI: 5.8 - 8.2 µm) and 8.0 µm (95%CI: 6.6 - 9.4 µm). The reproducibility of LCD was not significantly related to its magnitude (Figure 2), the visible laminar area or BMO-MRW (P > 0.15). The mean (SD) visible laminar area corresponded to 84 (26)% of the BMO area. Eyes with larger BMO-MRW had smaller visible laminar areas (P < 0.01).

Conclusions : The LCD can be measured with similar reproducibility with either BM or CSI reference planes. However, because the BM reference plane likely depends on choroidal thickness, which can vary with age and other factors, the CSI reference plane is likely more suitable for longitudinal studies.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.