Automated Quantification of Glaucomatous RNFL Reflectance Change using en-face OCT-Reflectance

Abstract

Purpose : To develop an automated method to quantify retinal nerve fiber bundle (RNFB) defect progression, in patients with glaucoma, captured by en-face OCT-Reflectance (OCT-R) scans.

Methods : Six eyes of 5 POAG patients with arcuate visual field defects were imaged at two visits 11-29 months apart using a SD-OCT system (Avanti RTVue-XR; Optovue). Ten 4.5x4.5mm circumperipapillary OCT-R scans were taken at each imaging session. The scans were then co-registered and averaged using ImageJ (PMID:28068370). A layer between the ILM and RNFL was extracted for analysis. The difference in illumination between scans was adjusted using background image correction based on the OCT-R choroid layer (76μm anterior to the RPE and the posterior limit of the OCT-R scan). Images with motion and specular reflectance artifacts were excluded. Remaining images were polar transformed for vertical representation of arcuate RNFB defects.

For each patient, within-visit variation of en-face OCT-R at 3.4mm from the optic disk was computed using the two baseline scans with the greatest difference in pixel-intensity variance. Difference in normalized pixel intensity was calculated between scans after excluding major blood vessels, and mean±SD of this pixel-intensity difference was computed.

RNFL defect progression was determined by similarly calculating pixel-intensity difference between the first baseline and follow-up scan and identifying regions 3.5 standard deviations or more below the mean baseline pixel-intensity.

Results : Thirteen regions of RNFL-defect progression were identified in five out of six eyes. Five inferior temporal progressions were revealed between 141.1° and 160.2° in three eyes, with a yearly change of 0.6°±0.8° (mean+SD) per eye in this region. Six superior temporal areas of progression were found between 196.2° and 224.3° in two eyes, with 3.7°±0.6° annual superior temporal progression per eye. Global yearly progression was 1.7°±2.2° per eye.

Conclusions : Comparison of RNFL reflectance change via en-face OCT-R provides an additional automated quantitative metric for identifying glaucoma progression. The regions of RNFB alteration can be delineated and compared to local changes in visual field defects, RNFL thickness, and OCT-Angiography perfusion.

This abstract was presented at the 2019 ARVO Imaging in the Eye Conference, held in Vancouver, Canada, April 26-27, 2019.