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Ocular blood supply
Anatomy & Optics
Key Points
- •Ophthalmic artery: first intracranial branch of the ICA; enters via optic canal; branches include CRA (inner retina - end artery, no anastomoses), SPCAs (~15-20, supply choroid/outer retina via choriocapillaris + optic nerve head prelaminar/laminar), LPCAs (2 - medial/lateral, travel to form major arterial circle of iris), ACAs (7 total - 2 per rectus except LR which has 1)
- •Two retinal circulations: (1) CRA → inner retina (NFL to inner OPL), low flow, high O2 extraction, autoregulated, inner BRB (tight junctions); (2) choriocapillaris (from SPCAs) → outer retina (photoreceptors/RPE by diffusion), highest blood flow per unit weight in the body, low O2 extraction, fenestrated, outer BRB at RPE level
- •Watershed zones: (1) optic nerve head (CRA vs SPCA territory) → AION (NAION: disc at risk + nocturnal hypotension; arteritic: GCA - emergency steroids to save fellow eye); (2) between SPCA territories → choroidal ischaemia (Elschnig spots); (3) between CRA branch territories → peripheral retinal non-perfusion
- •CRAO: sudden painless visual loss, cherry-red spot (thin foveola allows choroidal colour through; no inner retinal oedema at foveola); CRA is an end artery → inner retinal infarction within ~90-120 min; cilioretinal artery (present in 15-30%) → spares its territory; rule out GCA (ESR/CRP) in all patients >50
- •Venous drainage: CRV (within optic nerve, shares adventitial sheath with CRA at lamina cribrosa → CRVO), vortex veins (4-7, ~one per quadrant, posterior to equator → drain choroid/ciliary body/iris), anterior ciliary veins → all drain to superior/inferior ophthalmic veins (NO VALVES) → cavernous sinus; lack of valves → retrograde spread of infection → cavernous sinus thrombosis
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Keep reading Ocular blood supply
13 more sections are included with the Clinical plan.
- Definition
- Epidemiology
- Aetiology and causes
- Pathogenesis
- Classification
- Clinical features