Reading OCTA Scans: A Beginner's Guide to Vascular Layer Analysis

The Four OCTA Layers You Need to Know

OCTA systems separate the retinal vasculature into depth-resolved layers. Most platforms give you four standard slabs, and learning to read them in sequence is the foundation of systematic OCTA interpretation:

1. Superficial Capillary Plexus (SCP)

Inner retina — 70 μm below ILM

Highest vessel density, most sensitive to early diabetic changes. The SCP is where capillary non-perfusion first becomes visible in diabetic retinopathy. Also where you see most neovascularization activity in wet AMD.

2. Deep Capillary Plexus (DCP)

Middle retina — 70-170 μm below ILM

Situated in the outer plexiform and inner nuclear layers. More sensitive to ischemic injury than the SCP. DCP loss is a hallmark finding in diabetic macular ischemia and certain types of macular telangiectasia.

3. Outer Retina / Choriocapillaris Interface

Outer retina — Bruch's membrane level

In normal eyes, the outer retina is avascular. Any flow signal here in a patient over 50 should raise concern for choroidal neovascularization (CNV), which is the hallmark of wet AMD. The absence of normal outer retinal vessels is what you want to see here.

4. Choriocapillaris

Choroid — below Bruch's membrane

Dense vascular mesh supplying the RPE and outer retina. In AMD, you see focal flow void areas — regions where choriocapillaris perfusion is reduced — which precede and predict RPE atrophy progression.

A Systematic Approach to Reading Any OCTA Scan

When you open a new OCTA volume, don't start by hunting for pathology. Start with the systematic review:

Check scan quality first. Look for motion artifact lines, signal dropout at edges, and adequate signal strength. A low-quality scan is not diagnostically reliable — note the quality and reschedule if needed.
Review the superficial plexus. Map the foveal avascular zone (FAZ). Measure its area if your system provides this. An enlarged FAZ is a sign of diabetic or ischemic damage. Normal FAZ is roughly 0.25-0.5 mm².
Assess the deep capillary plexus. Compare density to the superficial layer. If DCP appears sparse relative to SCP, this is abnormal — correlates with ischemic pathology.
Examine the outer retina layer. Look for any flow signal in the avascular zone. Any flow here is pathological until proven otherwise — document it and refer or image further.
Check the choriocapillaris. Look for focal flow voids, especially in AMD patients. Geographic atrophy on structural OCT maps closely to choriocapillaris flow voids on OCTA.

Common Findings and What They Mean

Diabetic retinopathy: Early DR shows microaneurysms in the SCP, often as round or saccular dilations of capillary segments. As DR progresses, you'll see capillary non-perfusion areas — black patches on OCTA where vessels have closed. The DCP is frequently more affected than the SCP in moderate DR.

Wet AMD: The outer retinal layer is where CNV lives. A tangled vascular network — often described as a "glomerular" or "pruned" pattern — in the outer retina is the hallmark of choroidal neovascularization. You'll see it branching from the deep layer upward. Early CNV may only be visible on OCTA and not yet on structural OCT.

Glaucoma: The SCP shows区域性 vessel density loss in the peripapillary region in glaucoma. This appears as focal flow deficits that correlate with visual field defects, often before RNFL thinning is evident on structural OCT.

Normal Variants vs True Pathology

Some things that look abnormal on OCTA are actually normal:

Projection artifacts: Vessels from superficial layers can project downward and appear in deep layer images. Most modern systems have projection artifact removal — turn it on.
FAZ irregularity in older patients: Slight FAZ contour irregularity is common with age. Document it, but don't over-read it unless it's associated with vision loss or structural changes.
Flow void at the foveal center: The fovea is avascular — this is normal. What you don't want is flow signal inside the FAZ boundary where there should be no vessels.

Practice tip: Build a routine of reading one en face OCTA slab per patient per visit — even patients without retinal complaints. Consistency builds pattern recognition faster than case-based learning alone.

Go deeper: Our lesson on Vascular Layer Analysis covers the four layers in detail with real scan examples. Free to access — no subscription required.

Build your OCTA interpretation skills

Take our free OCT course — step-by-step lessons covering vascular layer anatomy, scan interpretation, and clinical application.

Start Free Course