Relating Retinal Blood Flow and Vessel Density in Sickle Cell Retinopathy

Abstract

Purpose : Previous studies have shown increased retinal blood flow and reduced capillary density due to sickle cell retinopathy (SCR). The purpose of the current study was to determine the relationship between retinal blood flow and vessel density in SCR subjects.

Methods : Imaging was performed in 15 subjects (3 control and 12 SCR) using a commercially available optical coherence tomography (OCT) instrument (Avanti, Optovue). A custom scan protocol and image analysis software was used for imaging a 2X2 mm area centered on the optic nerve head to generate enface Doppler OCT images and measure total retinal blood flow (TRBF). OCT angiography images of the superficial vascular plexus were acquired in a 6X6 mm retinal area centered on the fovea. Fractal dimension analysis computed the ratio of fractal dimension of each image pixel to its maximum fractal dimension (FDR). Vessel density was calculated as the ratio of vascularized area (0.7 ≤ FDR ≤ 1.0) relative to the total image area excluding the FAZ area. Vessel gap and non-vessel densities were similarly calculated based on areas with 0.3 < FDR < 0.7 and 0 ≤ FDR ≤ 0.3, respectively. Foveal avascular zone (FAZ) area was measured by processing connected components in the binary image. The relationship between TRBF and vessel parameters was determined by linear regression analysis. Significance was accepted at P≤0.05.

Results : Subjects’ mean age was 43 ± 13 years and ranged between 27 and 71 years. TRBF was 63 ± 31 microliter/min and ranged between 26 and 126 microliter/min. Vessel density was 67% ± 8% and ranged between 51% and 80%. TRBF was linearly related to vessel density (r²=0.36, P=0.02). The vessel gap density was 26% ± 5% and ranged between 17% and 33%. There was an inverse linear relationship between TRBF and vessel gap density (r²=0.35, P=0.02). Non- vessel density was 7.3% ± 3.7% and ranged between 2.3% and 15.7%. There was an inverse linear relationship between TRBF and non- vessel density (r²=0.34, P=0.02). There was no significant linear relationship between TRBF and FAZ area (r²=0.03, P=0.51).

Conclusions : Higher TRBF was associated with larger vessel densities and smaller vessel gaps and non-vessel retinal areas, suggesting blood flow compensation to augment oxygen delivery.

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