# En-Face Optical Coherence Tomography Angiography for Longitudinal Monitoring of Retinal Injury
## 3 Results
En-Face and OCTA: The C-scan of the data cubes were processed with a custom algorithm [36] to spatially enhance the microvasculature. The en-face volume was assessed for morphology changes throughout the depth (Figure 10). Once features were identified, 60 \(\upmu\)m optical slabs were projected into color depth-coded OCTA images for qualitative analysis (Figure 6). The inner retinal capillary layers identified were the Superficial Vascular Plexus (SVP), Intermediate Vascular Plexus (IVP), and Deep Vascular Plexus (DVP). The DVP (Figure 7) was most affected and analyzed in the following section (Figure 10). In the final images, motion artifacts still appear as banding, but the registration step minimizes the net effect. In the depth projections, the microvasculature is discernable from the background. Figure 5: The lesion dynamics presented as first derivative percent change (**a**) and as the second derivative (**b**). (**a**): Measurements of lesion parameters (width and height) as percent change with error bars for std. The CNV (red traces) parameters all show an increase in lesion size. Parameters: ONL lateral disruption, RPE lateral disruption, height of lesion, and photoreceptor layers (PR) measuring intrusion into ONL. The Acute injury lesions (black traces) show initial swelling in the RPE layer, but peaking at day 3 and overall change to reduced lesion size reaching steady state at day 7. The height of the acute injury lesions shows no change. (**b**): The percent difference plots of the lesion measurements (ONL, RPE, height, PR) are used to assess if the lesions are reaching steady state. When the difference between two timepoints, normalized by initial measurement values approaches zero asymptote, the steady-state region. The acute injury lesions (in black) rapidly approach the zero asymptote 3–7 days. The CNV lesions (in red), are oscillating about the zero crossing at day 21. The acute injury lesion followed the predictable progression of an early inflammatory phase response, peaking at 3 days and reaching steady-state around day 14 (Figure 5 Panel A). The phenotype of the lesions showed initial lateral growth of the hourglass shape, before collapsing into a pyramidal scar in the ONL. The en-face OCTA data in conjunction with the B-scan data show that acute injury lesions may acutely distort the RPE layer while the Bruch's membrane appears to remain intact. The inner retinal capillaries appear unaffected by the acute injury lesion and not an angiogenic response [47]. Figure 6: The longitudinal analysis of CNV as seen through both OCTA and High-Resolution B-Scans of lesion 1 reveals the inflammatory progression. Top row (**a–f**): The progression of inner retinal capillaries shows the day 3–14 non-perfusion of the vasculature as the inner layers are displaced by the edema and protrusions from the choroid. Middle Row (**g–l**): The choroidal layers show the lesion disruption that allows the vasculature infiltration of the retina. Bottom Row (**m–r**): The B-Scans of individual lesions over time tracks the swelling and edema formation in the early stage, then the neovascularization and scarring in the chronic phase. Scale bar 200 \(\upmu\)m.  
Figure 7: Disruptions of the inner retina capillaries are apparent when comparing the acute injury to CNV lesions. Thought the progression, the acute injury capillary bed is not disrupted (**a,b**). The formation of edema at day 7 in CNV (**c**) corresponds with the displacement of capillaries. At day 21 (**d**) most capillaries have returned to a normal distribution. Scale bar 200 \(\upmu\)m.  
Moreover, for acute injury lesions, the scarring is confined to the photoreceptor layers, presenting as the lesion from the IS/OS that protrudes into the ONL yet are asymptomatic of vascular leakage when analyzed with FA.