Overview
This lecture covers the fundamentals of interpreting Optical Coherence Tomography (OCT) for retinal disease, emphasizing key retinal anatomy, normal and pathological findings, and major differential diagnoses based on fluid location.
OCT Basics & Anatomy
- OCT is used for both quantitative (retinal thickness) and qualitative (structural interpretation) purposes.
- Retinal thickness is highly variable among individuals and best for patient follow-up rather than diagnosis.
- OCT images: hyperreflective (white, intense signal), hyporeflective/hypolucent (dark, low signal).
- The retina is visualized from vitreous (anterior) to choroid (posterior), with distinct anatomical layers.
- Key retinal layers (from inside out): internal limiting membrane (ILM), nerve fiber layer, ganglion cell layer, inner plexiform/nuclear layers, outer plexiform/nuclear layers, external limiting membrane, ellipsoid zone, interdigitation zone, RPE/Bruch's membrane.
- Choroid includes choriocapillaris, Sattler’s layer, Haller’s layer, and is bounded externally by the sclera.
Pathological Findings on OCT
- Intraretinal fluid (within retina) is seen in diabetic macular edema, vein occlusions, postoperative CME, uveitis, or medication toxicities (e.g., fingolimod, niacin, tamoxifen).
- Subretinal fluid (beneath retina, above RPE) indicates central serous retinopathy, wet AMD, macroaneurysm, retinal detachment, or tumor.
- Sub-RPE fluid (beneath RPE) is classic for pigment epithelial detachment, often in wet AMD or central serous.
- Retinal detachments present as large areas of subretinal fluid, often extending to periphery.
- Retinal tubules (circular areas with hyperreflective walls) resemble fluid but don't require treatment.
- Retinoschisis shows splitting of inner retina with vertical columns ("schisis cavities").
Special Conditions & Clinical Correlations
- Best disease shows subretinal vitelliform material, typically well-defined under the retina.
- Macular hole (full-thickness): complete break through all retinal layers at fovea; lamellar holes spare outer retina.
- Vein occlusion: localized retinal thickening with intraretinal fluid.
- Solar retinopathy: focal hyperreflectivity through ellipsoid zone.
- Plaquenil toxicity: paracentral loss of ellipsoid zone, thinning of outer nuclear layer, and downward displacement of inner layers.
- Angioid streaks: linear breaks in Bruch’s membrane, risk of choroidal neovascularization.
- Epiretinal (pre-retinal) membranes: surface wrinkling, retinal distortion, possible pseudoholes or schisis.
- Vitreomacular traction: partially detached cortical vitreous pulling on fovea, may cause schisis or full-thickness holes.
Key Terms & Definitions
- OCT (Optical Coherence Tomography) — an imaging technique for detailed cross-sectional retinal anatomy.
- Hyperreflective — brighter (white) zones; more light reflected.
- Hyporeflective/Hypolucent — darker (black) zones; less light reflected.
- Ellipsoid zone — hyperreflective line, inner segment/outer segment junction of photoreceptors.
- Subretinal fluid — fluid between retina and RPE.
- Sub-RPE fluid — fluid beneath the retinal pigment epithelium.
- Vitreo-macular traction — adhesion of vitreous to macula, causing distortion or schisis.
- Epiretinal membrane — fibrosis on retinal surface, causing puckers.
- Drusen — deposits under RPE, sign of dry AMD.
- Retinoschisis — splitting of retinal layers, seen as schisis cavities.
Action Items / Next Steps
- Review OCT anatomy diagrams.
- Practice distinguishing fluid location on sample OCT images.
- Read about major retinal diseases (AMD, central serous, vein occlusion, diabetic edema).
- For those on Plaquenil, ensure consistent screening by OCT, visual fields, and autofluorescence.