AMD: OCT Findings & En Face Correlation

AMD: OCT Findings & En Face Correlation

Age-related macular degeneration is the leading cause of irreversible vision loss in adults over 50. OCT has transformed how we detect, stage, and monitor AMD — and en face imaging reveals the full geographic extent of disease that B-scan alone consistently underestimates.

Dry AMD: The Drusen Foundation

🔭 Clinical Reference — CC BY 4.0

AMD drusen on OCT (Fig.2). Left: hard drusen (small focal RPE elevations). Middle: cuticular drusen (triangular sub-RPE deposits with 'sawtooth' pattern). Right: drusenoid PED (broad, flat RPE elevation with homogeneous fill). — Kulyabin M et al. Sci Data 11:365 (2024), CC BY 4.0

Drusen are deposits between the RPE and Bruch's membrane. On B-scan, they appear as sub-RPE elevations — the RPE is lifted, creating an irregular baseline. Their characteristics carry prognostic weight:

Geographic Atrophy (GA)

GA represents complete loss of the RPE, Bruch's membrane, and overlying photoreceptors. On B-scan, the key features are:

• RPE loss: The bright RPE band disappears — enhanced light transmission to the choroid creates a characteristic "choroidal hypertransmission" (brighter choroid beneath the atrophic zone)
• EZ disruption: The ellipsoid zone is absent or severely attenuated over the atrophic area
• Outer retinal thinning: ONL and photoreceptor layers thin and eventually disappear
• Junction zone: At the GA border, you can often identify a "junctional zone" where EZ is intact but transitioning

En face imaging at the RPE slab transforms GA assessment: the atrophic area appears as a bright, well-demarcated zone (enhanced choroidal signal through absent RPE). This gives you an accurate lesion area measurement that drives monitoring frequency and trial eligibility decisions.

Wet AMD: Choroidal Neovascularization

🔭 Clinical Reference — CC BY 4.0

Wet AMD fluid compartments (Fig.3). SRF (subretinal fluid): hyporeflective space between RPE and photoreceptors. IRF (intraretinal fluid): cystoid spaces within retinal layers. Sub-RPE fluid: PED with fibrovascular fill. Each signals active exudation requiring treatment. — Kulyabin M et al. Sci Data 11:365 (2024), CC BY 4.0

CNV represents growth of abnormal vessels from the choroid through Bruch's membrane. On B-scan, the presentation depends on CNV type:

En Face Correlation: The AMD Advantage

En face views at the RPE and sub-RPE slabs are game-changers for AMD:

• RPE slab: Drusen appear as bright spots against the normal RPE. GA appears as areas of very bright choroidal signal (transmission defect). Reticular pseudo-drusen form a distinctive reticular pattern.
• Sub-RPE / Bruch's slab: Type 1 CNV shows as a lacy, irregular bright lesion. Drusenoid PED shows as a large confluent bright area.
• Outer retina slab: Photoreceptor loss over atrophy creates characteristic dark (low reflectivity) zones that map the functional loss area.

AMD Monitoring Protocol

• Intermediate AMD (medium drusen only): Annual OCT minimum; consider 6-month if soft drusen, RPD, or drusenoid PED
• Advanced dry AMD / GA: Every 6 months — monitor for wet conversion. GA growth rate ~1.7 mm²/year average but highly variable
• Treated wet AMD: Follow your treating retinologist's protocol; typically monthly initially, then T&E or PRN
• Fellow eye with wet AMD: 25–50% 5-year fellow eye conversion risk; minimum every 6 months

Key Takeaways

• Drusen type and size predict progression risk — soft drusen and RPD carry the highest risk
• GA shows as choroidal hypertransmission on B-scan; en face gives accurate lesion area
• CNV type (1, 2, 3) guides treatment urgency and expectation of response
• Always assess the en face RPE slab — B-scan alone underestimates disease extent
• Fellow eye of wet AMD needs minimum 6-month monitoring