Impact of the scan field on flow measurements in Optical Coherence Tomography Angiography (OCTA) images of diabetic eyes

Abstract

Purpose : To evaluate the impact of the scan field in Optical Coherence Tomography Angiography (OCTA)-derived flow parameters in images captured with the 3 commercially available scanning protocols (3x3 mm, 6x6 mm and 8x8mm) of the Cirrus HD-OCT device (Carl Zeiss Meditec, Dublin, CA, USA) in a cohort of diabetic eyes from a larger OCTA trial (ClinicalTrials.gov, NCT03422965).

Methods : 60 diabetic eyes underwent prospectively OCTA imaging using the 3 scanning protocols. Images were processed using custom-made research software (University of Washington, Seattle, US) to obtain measurements in both the superficial and deep capillary plexus (SCP and DCP, respectively) of vessel diameter (VD), vessel area density (VAD), vessel skeleton density (VSD), vessel perimeter index (VPI), vessel complexity index (VCI), flow impairment (FI) and flux. Differences between scanning protocols and correlations between measurements and relevant clinical data were determined.

Results : Significant differences were observed in all the parameters in the SCP and DCP when comparing the measurements in the 3x3, 6x6 and 8x8 mm scans (p<0.001 in all cases). However, a significant correlation was observed in both the SCP and DCP between the VAD of the 3x3 and the 6x6 mm (SCD 0.70, p<0.001, DCP 0.51, p<0.001) and 8x8 mm scans (SCP 0.66, p<0.001, DCP 0.50, p<0.001). Significant differences in VAD were observed in the DCP between no DR and proliferative DR eyes in the 3x3 (0.33 vs 0.29, p=0.007) and 6x6 mm (0.40 vs 0.39, p=0.014) but not in 8x8 mm scans (0.44 vs 0.43, p=0.27).

Conclusions : Quantification of OCTA parameters cannot be directly extrapolated from a small scan field (i.e. 3x3 mm) to a larger field (i.e. 6x6 or 8x8 mm). One of the major limitations of OCTA is the decreased quality of the images as the scan area increases. The advent of wide field OCTA devices will provide an interesting opportunity to evaluate the extent of the differences reported.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Composite image of a study eye. Superior row (A, B, C), superficial capillary plexus. Inferior row (D, E, F), deep capillary plexus. OCTA 3x3 mm (A, D), OCTA 6x6 mm (B, E), OCTA 8x8mm (C, F).

 

Correlation of vessel area density measurements in superficial and deep capillary plexuses (SCP and DCP, respectively) in 3x3mm, 6x6mm and 8x8mm.