Normal Anatomy on OCT: Retinal Layers, Vitreoretinal Interface, Choroid and Optic Nerve Head
Reading the retina from inside out
On a normal macular B-scan the bands run: ILM (hyperreflective, first interface with vitreous), RNFL, GCL, IPL (hyperreflective), INL (hyporeflective), OPL (hyperreflective, contains Henle fibre layer temporally), ONL (hyporeflective), then the four outer bands - ELM, ellipsoid zone (EZ, formerly IS/OS junction), interdigitation zone (IZ), and the RPE/Bruch membrane complex. The EZ is the single most clinically weighted band: its continuity tracks photoreceptor integrity. The RPE and Bruch membrane are usually resolved as one hyperreflective complex on standard scans; do not claim to see them separately unless the scan proves it.
Fovea and vitreoretinal interface
At the foveola the inner layers are displaced eccentrically (clivus), the ONL is thickest, and the RNFL disappears. The vitreous is normally hyporeflective/optically empty with a barely visible posterior hyaloid; a separated hyaloid appears as a faint reflective line with a Weiss ring nasally.
Choroid
Below Bruch membrane sit the choriocapillaris, Sattler layer (medium vessels) and Haller layer (large vessels), then the chorioscleral interface. Choroidal thickness is measured perpendicular from Bruch membrane to that interface; subfoveal values vary widely (roughly 250–300 µm in normal young eyes) and are higher in pachychoroid and lower in high myopia and atrophy.
Optic nerve head
Disc-centred scans show Bruch membrane opening (BMO), prelaminar tissue, the lamina cribrosa with its pore pattern, and the peripapillary RNFL, which is thickest superiorly and inferiorly.
Traps: mislabelling the IZ as the EZ; calling a double line the RPE when it is RPE plus Bruch; assuming a hyporeflective band is fluid when it is the INL or ONL; forgetting that Henle fibres sit in the OPL and can mimic fluid in oblique scans.
Rule of thumb: count the four outer bands (ELM, EZ, IZ, RPE/Bruch) - if you can account for all four, your layer identification is almost certainly correct.