Enhanced Glaucoma Detection With An Anatomically Accurate Spectral Domain OCT Derived Neuroretinal Rim Parameter

Abstract

 

Purpose:

 

Rim assessment based on the clinical disc margin (DM) lacks a solid anatomical basis for two reasons. 1) the DM is not a reliable outer border of rim tissue due to clinically and photographically invisible extensions of Bruch’s membrane (BM) inside the DM¹ and 2) rim tissue orientation in the ONH is unaccounted for. We introduced a parameter, BM opening-minimum rim width (BMO-MRW),² that quantifies the rim from its true anatomical outer border and accounts for its variable trajectory in the measurement plane. Here we report its diagnostic capability.

 

Methods:

 

Glaucoma patients (n = 107) and normal controls (n = 48) had Spectralis SD-OCT imaging (24 B-scans centred on the optic nerve head). The median (IQR) age and mean deviation were 69.9 (64.3, 76.9) and 65.0 (58.1, 74.3) yrs, and -3.92 (-7.87, -1.62) and 0.33 (-0.32, 0.98) dB respectively. The internal limiting membrane (ILM) and BMO were manually segmented in all B-scans and two parameters (Fig 1) derived with custom software: 1) BMO-horizontal rim width (BMO-HRW), the distance between BMO and ILM in the BMO reference plane, akin to current BMO-based measurements and 2) BMO-MRW, the minimum distance between BMO and ILM. Global and 6 sectoral Moorfields Regression Analysis (MRA) from Heidelberg Retina Tomograph scans yielded MRA1 and MRA 2 where "borderline" was classified as normal and abnormal respectively. Diagnostic performance was evaluated in Receiver Operating Characteristics (ROC) space.

 

Results:

 

In controls, BMO-MRW was significantly more correlated to age than BMO-HRW (r = -0.26 and -0.06, P <0.01) or BMO area (r = -0.46 and -0.07, P < 0.01). Global BMO-MRW had consistently higher discrimination than global BMO-HRW (Fig 2). At 95% specificity, the sensitivity of BMO-MRW was 83% and BMO-HRW, 25%. Both MRA1 and MRA2 performed substantially worse. Sectorally, at 95% specificity, the sensitivity of BMO-MRW ranged 56-81%, and BMO-HRW, 10-46%. BMO-MRW performed better than MRA1 or MRA2 in all sectors.

 

Conclusions:

 

The >3-fold higher sensitivity at 95% specificity in early glaucoma of BMO-MRW compared to current methods is clinically significant, indicating a new structural marker for the detection and risk-profiling glaucoma.¹Reis et al, Ophthalmology (in press)²Reis et al, submitted  

 

Keywords: optic disc • imaging/image analysis: clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)