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Superficial & Deep Capillary Plexus

Two vascular layers, two different clinical stories. Learn to differentiate superficial vs deep pathology using en face segmentation.

Superficial & Deep Capillary Plexus: Reading Flow Maps

The retinal vasculature is organized into two distinct capillary networks at different depths. The superficial capillary plexus (SCP) runs in the ganglion cell and nerve fiber layers. The deep capillary plexus (DCP) occupies the border between the inner nuclear and outer plexiform layers. These are not the same structure — they serve different functions, respond differently to disease, and require separate interpretation.

OCTA separates these plexuses into individual en face slabs. Reading them independently — rather than looking only at a combined slab — is how you avoid missing early ischemia, subtle CNV, and plexus-specific disease changes.

Vascular Anatomy Refresher

Retinal Vascular Plexus Layer AnatomyILM — Inner Limiting MembraneSUPERFICIAL CAPILLARY PLEXUS (SCP) — GCL / IPL borderInner Plexiform Layer (IPL)DEEP CAPILLARY PLEXUS (DCP) — INL / OPL borderOuter Plexiform Layer (OPL)Outer Nuclear Layer — avascularSCP: large capillaries in NFL/GCL • DCP: fine capillaries at OPL, most disease-sensitiveOCTA slabs must be calibrated to each layer boundary for valid plexus imaging

Retinal vascular plexus anatomy: SCP at GCL/IPL, DCP at INL/OPL — Educational illustration, not a clinical scan

Understanding which disease processes affect which plexus requires knowing where each plexus lives in the retinal layer stack.

The SCP spans from the ILM to approximately the middle of the inner plexiform layer. It contains the larger retinal arterioles and venules that form the major vascular arcades visible on fundus photography. The SCP is the reference layer in most OCTA software — its arcades and FAZ boundary serve as the coordinate system for all other flow measurements.

The DCP occupies the boundary zone between the INL and OPL. It is composed of fine, densely packed capillaries that form a honeycomb mesh pattern on en face. The DCP is metabolically critical — it supplies the high-oxygen-demand photoreceptors indirectly via the ONL and provides the primary vascular input to the inner nuclear layer.

  • Intermediate capillary plexus (ICP): some software identifies a third plexus between SCP and DCP; clinically, SCP and DCP are the two primary diagnostic layers
  • Avascular zone: the ONL and outer retina have no capillaries — they are nourished by the choriocapillaris through diffusion
  • Slab calibration: software segmentation must correctly identify the GCL/IPL boundary for SCP and the INL/OPL boundary for DCP — errors here produce artifactual signal
  • Projection artifact: SCP vessel shadows project onto the DCP slab — this is a common source of false-positive "flow" on DCP; use projection-removal algorithms when available
Key principle: When you see an abnormality on OCTA, always identify which plexus it occupies before interpreting it. The same-appearing dark area on SCP vs DCP has different differential diagnoses.

SCP Reference Layer

Superficial Capillary Plexus (SCP): Reference LayerSCP En Face — Normal appearanceFAZLarge arcades clearly visibleSCP clinical role• Reference for all flow quantification• Major arcades: temporal superior/inferior• Less sensitive than DCP for ischemia• Glaucoma: focal RNFL wedge defects• DR: microaneurysms dot-like bright foci• BRVO: non-perfusion zones = dark sectorsSCP provides vascular roadmap; pathological SCP changes lag behind DCP

SCP en face: arcade pattern, FAZ boundary, reference layer for flow maps — Educational illustration, not a clinical scan

The SCP en face slab should be your first stop when reviewing any OCTA. It gives you the vascular roadmap: the location of the major arcades, the FAZ boundary on the SCP, and any large vessel abnormalities.

On a normal SCP slab, you see a symmetric arcade pattern with the superior and inferior temporal arcades framing the macula. The FAZ appears as a clearly demarcated avascular zone centered on the fovea, with a regular oval boundary and average area of 0.3 mm².

SCP in glaucoma: The primary OCTA biomarker for glaucoma is focal loss of capillary flow in the SCP, corresponding to RNFL wedge defects. This appears as a dark sector in the superior or inferior arcuate zone, matching the RNFL thinning on the thickness map. OCTA can detect SCP flow loss before visual field defects are measurable.

SCP in DR: Microaneurysms appear as small bright dots on the SCP slab (high flow foci). Non-perfusion zones appear as dark areas where capillary density is lost. Early NPDR may show only scattered microaneurysms; advanced PDR shows large NP areas that correlate with cotton-wool spot distribution on fundus photography.

  • BRVO: sectoral non-perfusion on SCP within the territory of the occluded vein
  • CRVO: diffuse reduced flow across all four quadrants of SCP and DCP
  • SCP FAZ: regularly round in health; irregular, scalloped margins suggest capillary dropout at the FAZ boundary
  • Superficial CNV (type 2): high-flow vascular network on SCP level above the RPE — rare but important

DCP Sensitive Layer

Deep Capillary Plexus (DCP): The Disease-Sensitive LayerDCP Normal — denser capillary meshFAZFine honeycomb meshDCP in DR — ischemia / cystsIschemiaCystMADCP: ischemia zones, cysts, microaneurysmsDCP detects ischemia and DME earlier than SCP — always examine both slabs

DCP en face: normal honeycomb mesh vs ischemia/cysts in DR — Educational illustration, not a clinical scan

The DCP is where early ischemic disease becomes visible before clinical symptoms appear. It is more susceptible than the SCP because its capillaries are smaller, have less redundancy, and are under higher metabolic demand. In diabetic retinopathy specifically, DCP changes precede SCP changes in the natural history of ischemia.

Normal DCP on OCTA shows a fine honeycomb mesh of uniform density — denser than the SCP, with capillaries packed tightly together and no large vessel shadows. The DCP FAZ is typically slightly larger than the SCP FAZ.

DCP in DME: Intraretinal cysts (pseudocysts) in DME expand in the OPL and INL — exactly where the DCP runs. Cysts appear as dark holes in the DCP flow map with disruption of the surrounding capillary mesh. The cyst size and location on DCP correlates with visual acuity better than central subfield thickness alone.

DCP ischemia: Non-perfusion zones on DCP appear as dark areas devoid of capillary signal. In DR, DCP NP often precedes SCP NP by several ETDRS steps. This is why OCTA can restage DR patients who appear lower-risk on fluorescein angiography.

  • DCP cysts: dark round voids within the capillary mesh; track size and number at each visit as a surrogate for DME severity
  • DCP flow density: automated quantification available on most OCTA platforms; values below 40% in the parafoveal zone are associated with reduced acuity
  • Projection artifact on DCP: always use projection-artifact removal; without it, SCP vessel shadows create false bright bands on DCP
  • DCP in AMD: Type 1 CNV (sub-RPE) can appear as abnormal flow at or just above the DCP level; correlate with structural en face RPE slab

Disease-Specific Patterns

Plexus Patterns by DiseaseDR/DMENP zoneCystsNP + MAs + cystsGlaucoma (SCP)RNFL wedge defectFocal arcuate flow lossBRVO (SCP)NP sectorSectoral non-perfusionAMD (DCP)CNV flow loopType 1/2 CNV on DCPEach disease stamps a characteristic pattern — pattern recognition speeds diagnosis

Disease-specific plexus signatures: DR, glaucoma, BRVO, AMD — Educational illustration, not a clinical scan

Each major retinal disease produces a characteristic signature when the SCP and DCP are examined together. Developing fluency with these patterns allows rapid triage at the OCTA workstation.

Diabetic retinopathy: The DR pattern is defined by the triad of microaneurysms (bright dots, SCP), intraretinal cysts (dark voids, DCP), and non-perfusion zones (dark sectors, both plexuses). The DCP is typically more involved than the SCP at equivalent stages. Neovascularization at the disc or elsewhere (NVD/NVE) appears as a frond-shaped high-flow network on the SCP slab extending anterior to the ILM.

Glaucoma: Focal arcuate capillary loss on SCP, corresponding to the RNFL map. DCP is relatively preserved in glaucoma compared to DR. Whole-image capillary density metrics from OCTA have been shown to correlate with mean deviation on Humphrey VF with R² approaching 0.7 in advanced disease.

RVO: Branch RVO shows sectoral involvement respecting the horizontal meridian (BRVO) or the quadrant of the affected vessel. CRVO shows global flow reduction. Ischemic RVO shows large NP zones on both SCP and DCP; non-ischemic shows preserved flow with perivascular cuffing.

AMD: Type 1 CNV (occult) appears on DCP or just below it as a lacy vascular network. Type 2 CNV (classic) appears on SCP above the RPE. Type 3 (retinal angiomatous proliferation, RAP) appears as a high-flow focus at the DCP level communicating with a sub-RPE component.

FAZ Metrics & Interpretation

FAZ Metrics and Clinical InterpretationFAZ measurementsHWPerim.Area: 0.3 mm² avg (0.2-0.4 normal)Perimeter irregularity index = roundnessFAZ clinical significanceEnlarged FAZDME, DR, RVO, sickle cellIrregular FAZIschemia, capillary dropoutAsymmetric FAZBRVO sector, focal ischemiaSmall FAZHigh myopia, artifactSCP vs DCP FAZDCP FAZ larger, more sensitiveSerial FAZ areaIschemia progression trackingFAZ area and perimeter irregularity: quantitative biomarkers for ischemic burden

FAZ dimensions and clinical interpretation across disease states — Educational illustration, not a clinical scan

The foveal avascular zone is the most quantifiable biomarker available from OCTA. It requires no dye, no timing, and no subjective reading — the software measures it automatically from the SCP and DCP slabs.

Normal FAZ parameters: Area 0.2–0.4 mm², approximately circular with a perimeter irregularity index (acircularity index) close to 1.0. The DCP FAZ is typically 20–30% larger than the SCP FAZ due to the finer capillaries and different layer geometry at the DCP level.

Enlarged FAZ: The most common abnormality. Seen in DME (ischemic), sickle cell retinopathy, RVO, and advanced DR. A FAZ area above 0.5 mm² on SCP should prompt careful review of the DCP for dropout and quantification of parafoveal flow density.

Irregular FAZ: Scalloped or jagged FAZ margins indicate focal capillary dropout at the FAZ boundary. This is an early sign of ischemia and may precede enlargement. A perimeter irregularity index above 1.6 is associated with reduced acuity in DR patients independent of FAZ area.

  • Serial FAZ monitoring: FAZ area is a reproducible, inter-visit stable metric — enlargement of more than 0.05 mm² between visits is clinically significant
  • FAZ asymmetry: compare fellow eye FAZ; asymmetry above 0.1 mm² suggests unilateral ischemic process
  • Pediatric caution: FAZ area is smaller in children and increases with myopia — use age-matched normative data
  • High myopia: FAZ may appear artificially enlarged due to choroidal image stretching; correlate with axial length
SUPERFICIAL vs DEEP CAPILLARY PLEXUS — DEPTH SLABS SUPERFICIAL CAPILLARY PLEXUS ILM → IPL (0–20 µm below ILM) FAZ Large arcade vessels · clear FAZ DEEP CAPILLARY PLEXUS INL → OPL (50–85 µm below ILM) NPA dropout Dense capillary honeycomb · DR dropout

Educational illustration — SCP (teal, left) vs DCP (indigo, right): depth slabs, FAZ, capillary density pattern, and DR non-perfusion dropout. Not a clinical scan.

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In This Course

1. ILM Surface Analysis2. Superficial & Deep Capillary Plexus3. Outer Retina & RPE/Bruch's Complex4. Choriocapillaris & Choroid5. 10 Management-Changing Clinical Scenarios6. Artifacts, Segmentation Errors & Documentation