Comparison of Reference Planes in Volumetric SD OCT for Optic Nerve Head Morphometry

Abstract

 

Purpose:

 

Reference plane variability in SLO has been observed as a source of measurement error in time course studies of optic nerve head (ONH) morphometry. The purpose of this study was to investigate the longitudinal stability and inter-rater reliability of the Bruch’s Membrane Opening (BMO) as a reference plane for morphometric analysis of the human ONH in SD OCT images.

 

Methods:

 

ONH images of healthy human volunteers were acquired using a prototype SD OCT system. The BMO, Bruch’s Membrane (BM) and Inner Limiting Membrane (ILM) were manually delineated on every second B-scan in the SD OCT volumes (Fig 1) by 3 delineators on 3 different occasions. The SD OCT measurements were validated by calculating the cup volume using the conventional reference plane and comparing it to values obtained with SLO. The variability of post-BMO cup volume measurements (using the BMO as a reference plane) between delineations was calculated. The disc margin was identified in the SD OCT B-scans as the BMO. The SD OCT delineation was compared to the clinical disc margin from stereo disc photography (SDP) by directly overlaying the images and scaling to match landmarks.

 

Results:

 

The SD OCT cup volume measurements were consistent with the SLO values to within experimental error. The post-BMO cup volume variability over all delineations (intra- and inter-rater) had a coefficient of variance of < 0.01. The delineation of the disc margin in the SD OCT corresponded to the disc margins from SDP.

 

Conclusions:

 

The BM is a highly reflective surface which is easily detected by SD OCT. The high planarity BMO permitted correction of the volume tilt during acquisition. The SD OCT measurements of cup volume, rim area and cup area were validated with respect to SLO. Delineation of the BMO corresponded to a slightly larger area than the clinical disc margin. The results of this study provide a foundation to investigate the BMO as stable reference plane in clinical glaucoma.  

 

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