Introduction to En Face Views
Your first look at the coronal plane. Understand how en face images are generated from volumetric OCT data and why they reveal what B-scans miss.
Introduction to En Face Views
This is where everything changes. En face OCT shows you the retina from above — the coronal plane — rather than in cross-section. It's like switching from a side view of a building to a floor plan. Both are useful; together, they're transformational.
How En Face Images Are Generated
Every volumetric OCT scan acquires a 3D cube of data — typically 512 × 128 or 512 × 512 A-scans covering a 6mm × 6mm area. An en face image is created by:
- Choosing a layer or slab: The software selects a horizontal plane at a specific retinal depth (e.g., the RPE, the EZ, or a slab spanning multiple layers)
- Mapping reflectivity: At each (x,y) position, the reflectivity value at that depth becomes a pixel brightness
- Displaying as a 2D image: The result is a top-down view of that retinal layer
Think of it like slicing a CT scan horizontally. Each slice shows a different "floor" of the retina.
Structural En Face vs. OCT Angiography
| Feature | Structural En Face | OCTA En Face |
|---|---|---|
| What it shows | Tissue reflectivity (anatomy) | Blood flow (motion contrast) |
| Requires | Standard OCT volume scan | Repeated B-scans + motion analysis |
| Best for | Drusen mapping, ERM extent, GA boundaries, fluid distribution | CNV detection, ischemia, FAZ assessment |
| Available on | All modern SD-OCT and SS-OCT | OCT-A capable devices only |
Important: You don't need OCTA hardware to use en face imaging. Every volumetric OCT scan already contains the data for structural en face views. Most devices generate them automatically — you just need to know how to read them.
Key En Face Slabs
Different slab depths reveal different pathology:
- ILM slab: ERM extent, vitreomacular traction footprint, inner retinal surface irregularities
- RNFL slab: Nerve fiber layer defects (glaucoma), peripapillary atrophy patterns
- Inner retina slab (GCL → OPL): Cystoid spaces in DME/RVO, paracentral acute middle maculopathy
- Outer retina slab (ONL → EZ): Subretinal fluid extent, outer retinal tubulations, photoreceptor damage footprint
- RPE slab: Drusen map, geographic atrophy boundaries, RPE detachments, hyperreflective foci
- Sub-RPE / Bruch's slab: Drusenoid PED extent, basal deposits, type 1 CNV (sub-RPE neovascularization)
- Choroidal slab: Pachyvessel pattern, Haller layer vessel dilation, choroidal thickness maps
Reading En Face: What to Look For
En face images use brightness = reflectivity:
- Bright spots/areas: High reflectivity at that depth — could be normal tissue, hard exudates, or fibrosis
- Dark spots/areas: Low reflectivity — could be cysts (fluid), shadowing from above, or tissue absence (atrophy)
- Patterns: Round dark circles = cysts. Irregular dark patches = atrophy. Bright rings = drusen margins. Branching dark lines = vessels (on OCTA)
Always correlate with B-scan. En face gives you the map; B-scan gives you the depth. Use both together.
Key Takeaways
- En face = coronal view generated from volumetric OCT data. No special hardware needed
- Different slab depths reveal different pathologies
- En face reveals geographic extent that B-scans underestimate
- Structural en face (reflectivity) is different from OCTA (blood flow)
- Always correlate en face findings with the corresponding B-scan
Educational illustration — How en face imaging works: 3D OCT volume → depth slab selection → coronal projection. Not a clinical scan.
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