Quantitative analysis of conjunctival microvasculature imaged using optical coherence tomography angiography

Background:The goal was to quantitatively analyze the bulbar conjunctival microvascular density using optical coherence tomography angiography(OCTA)and compare it to the vessel density using functional slit-lamp biomicroscopy(FSLB).Methods:Temporal bulbar conjunctiva of 20 eyes(10 healthy subjects)was imaged using both OCTA and FSLB.Image processing was performed including equalization,de-noising,thresholding,and skeletonization.The vessel density was measured by fractal analysis(box counting,Dbox)and pixel counting(%).Results:Vessel density(Dbox)of the bulbar conjunctiva obtained using OCTA was 1.28±0.01 Dbox,which was significantly lower than the result(1.32±0.01 Dbox,P<0.001)obtained using FSLB.Furthermore,the vessel density(%)obtained using OCTA was 3.31±0.12%,which was also significantly lower than the result(3.69±0.16%,P<0.001)obtained using FSLB.No significant correlations(r ranged from 0.21 to 0.32,P>0.05)between both instruments were found in both vessel density methods(Dbox and percentage).However,in each of the devices,vessel density in Dbox was significantly correlated with the vessel density in percentage(r=1.0 for FSLB and r=0.98 for OCTA,both P<0.001).Conclusion:This study demonstrated that the vessel density of the bulbar conjunctiva obtained using OCTA can be quantified,and the results were not compatible with that obtained using slit-lamp biomicroscopy photography.