Comparison between optical coherence tomography angiography and fundus fluorescein angiography for early detection of diabetic retinopathy
Authors: Badr Amal S.S. , El-Baha Samir M. , Souka Ahmed A.R. , Goma Amir R. 
Published: May 2024

Purpose
This work studied the ability of optical coherence tomography angiography (OCTA) to detect and analyze microvasculature changes in the retina in early nonproliferative diabetic retinopathy (NPDR) compared with fluorescein angiography (FA) regarding the posterior pole. The study compared two groups of patients with NPDR, a group with diabetic macular edema (DME) and another group without DME, with a group of health individuals as the control. The study compared foveal avascular zone (FAZ) size, capillary perfusion (CP), and vessel density in the superficial capillary plexus (SCP) in both the control and the two groups of patients with NPDR with and without DME. The number of microaneurysms (MAs) was also analyzed in the SCP and deep capillary plexus of OCTA and compared with FA.

Patients and methods
The study included 40 eyes of patients with NPDR and 20 eyes of volunteers as control. FA, OCT, and OCTA were done for all 40 eyes of NPDR, and only OCTA was done for the control group. OCTA parameters were as follows: ‘vessel density (mm/mm2), CP (%) (in SCP), and FAZ area (mm2) in SCP of macular area.' OCTA was performed using both 3×3 mm and 6 × 6 mm scans of the OCTA and with production of an OCT macular map. Digital color fundus photography and FA photographs were analyzed in relation to NPDR with evaluation of;Deg;MA;Deg;s, FAZ appearance, and late dye leakage. For;Deg;MA;Deg; counting, a 3×3 mm section centered on the fovea was manually delimited on FA images.

Results
MA count comparison between FA and OCTA (SCP and deep capillary plexus) showed highly a statistically significant differences between them, with P value less than 0.001 in all cases. DMI appeared early in all eyes with NPDR, presented with vessel density, CP, and the FAZ area in the SCP in both groups of patients with NPDR (in group A without DME and in group B with DME), with no significant statistical difference between the two groups of NPDR. Group A had a mean±SD vessel density of 9.95±2.805 mm/mm2, mean±SD of CP 18.97±4.754%, and mean±SD FAZ size of 0.59±0.228 mm2, whereas in group B, mean±SD vessel density was 10.19±3.152 mm/mm2, mean±SD CP was 20.14±6.131%, and mean±SD FAZ size was 0.63±0.270 mm2. When comparing groups A and B of patients with NPDR with the control group (group C), the control group showed a mean±SD vessel density of 13.23±2.454 mm/mm2, mean±SD of CP 27.89±5.627%, and mean±SD FAZ size of 0.36±0.097 mm2. A highly significant difference was found between patients with NPDR (both groups A and B) and healthy participants (group C).

Conclusions
MAs are more prominent in FA than in OCTA. Superficial vessel density and CP of macular region in NPDR eyes with and without DME are both decreased, in correlation to control group. The FAZ region of patients with NPDR is also enlarged when compared with healthy participants. CP and vessel density cannot be evaluated by FA, which is an advantage of OCTA over FA, but by using FA, we can evaluate the periphery, which cannot be evaluated by OCTA up till now.