400kHz Optical Coherence Tomography Angiography based capillary density assessment in 3D vs 2D as a potential biomarker of retinal neurodegeneration

Abstract

Purpose : To apply high speed OCT angiography in the peripapillary region for evaluation of the vessel density from 3D volumes as opposed to 2D projections in glaucoma patients with a notch sign and compare it with the RNFL thickness measured with an SD-OCT device.

Methods : A SS-OCTA system at 1060 nm was scaled to 400kHz using intra-spectral scanning. High speed enables calculating high contrast angiographies over 20° Field of View. The angiographic signal was used to calculate the mean vessel density (MVD) of peripapillary capillaries in angular sectors masking out vessels >50µm. For 3D analysis, the RNFL/ganglion cell layer down to the outer plexiform layer have been segmented using a graph based approach. Projection artifacts have been reduced using a weighted substraction of superficial layers. We compare MVD obtained in 3D to MVD extracted from 2D projection maps. The sectorial MVDs are compared with RNFL thickness measurements using a commercial SD-OCT device employing a peripapillary ring scan pattern.

Results : The 400kHz OCTA system was used to image 9 glaucoma patients with notch sign allowing comparing areas with a present notch and without. The MVD was calculated in 2D and 3D for a more robust interpretation of microvascular structures. The measured values were compared with RNFL thickness measurements. The MVD was 0.0956 ± 0.014 for non-notch regions and 0.0787 ± 0.015 for notch segments in 2D and 0.0581± 0.0077 for non-notch segments and 0.497 ± 0.0112 for notch segments in 3D. The deviation value of the RNFL thickness to standard values was measured with SDOCT resulting in 0.53 ± 0.074 % deviation in the notch sector and 0.865 ± 0.18 % in the non-notch sector; this difference was statistically significant (p = 0.008). Easy visual correlation of MVD with RNFL thickness maps is found by overlaying color coded MVD plots to OCTA (see figure).

Conclusions : Our preliminary results in glaucomatous eyes with notch sign indicate that OCTA based MVD measurements allow to distinguish between atrophic and nonatrophic RNFL sectors. This strengthens further the potential of MVD as potential biomarker for neuro-retinal degeneration. 3D MVD does not indicate a statistically significantly improvement as opposed to standard evaluation on 2D projections.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Glaucomatous retina with notch defect: (lhs) Overlay of color coded MVD to OCTA (rhs) RNFL thickness plot.