Overview
This lecture covers the ocular blood supply, focusing on the branches of the ophthalmic artery, arterial supply to the retina, optic nerve, choroid, eyelids, conjunctiva, extraocular muscles, and clinical correlations.
Ophthalmic Artery and Its Branches
- The ophthalmic artery originates from the internal carotid artery and enters the orbit medial to the anterior clinoid process.
- Its first branch is the central retinal artery, which supplies the inner six layers of the retina (not the fovea).
- Other major branches include the lacrimal artery (supplies lacrimal gland and eyelids) and the muscular arteries (medial and lateral).
Central Retinal Artery
- Travels under the optic nerve, enters it, and then branches into superior and inferior trunks with nasal and temporal branches.
- Supplies the inner six layers of the retina; the fovea is supplied by the choroidal (ciliary) circulation.
- Central retinal artery occlusion causes retinal edema and "cherry red spot" due to preserved foveal circulation.
- In 20% of people, a cilioretinal artery (from ciliary circulation) can preserve central vision in central retinal artery occlusion.
Posterior Ciliary Arteries
- Two types: short (10–20 branches) and long (medial and lateral).
- Short posterior ciliary arteries supply the choroid (posterior to equator) and outer four retinal layers, form the circle of Zinn-Haller around optic disc.
- Long posterior ciliary arteries run in the suprachoroidal space and join anterior ciliary arteries to form the major arterial circle of the iris.
Blood Supply of Retina, Optic Nerve, and Choroid
- Inner six retinal layers: central retinal artery.
- Outer four retinal layers: choroidal (ciliary) circulation via short posterior ciliary arteries.
- Optic nerve head blood supply mainly from the posterior ciliary arteries; segmental supply explains altitudinal field defects in anterior ischemic optic neuropathy (AION).
Muscular and Anterior Ciliary Arteries
- Muscular arteries supply extraocular muscles and give rise to anterior ciliary arteries.
- Each muscle has two anterior ciliary arteries except the lateral rectus, which has one.
- Anterior ciliary arteries form part of the major arterial circle of the iris; damage can cause anterior segment ischemia.
Other Major Branches and Terminal Arteries
- Supraorbital artery supplies the forehead and scalp.
- Anterior and posterior ethmoidal arteries supply the sinuses.
- Terminal branches: supratrochlear and dorsal nasal arteries.
- Palpebral arteries (from dorsal nasal and lacrimal) form arcades in eyelids.
Venous Drainage
- Vortex (vorticose) veins (usually 4–7) drain the choroid into the superior and inferior ophthalmic veins.
- Their position helps identify the equator of the eye; attached sites explain lobular choroidal detachment patterns.
- Anterior ciliary veins follow arteries, drain into vortex veins.
Clinical Nuggets
- Central retinal artery occlusion: cherry red spot, vision loss except in cilioretinal artery presence.
- AION: segmental blood supply leads to altitudinal visual field defects (often inferior field loss).
- Anterior segment ischemia risk increases with surgery on more than two recti muscles, especially vertical muscles.
- Scleral buckling can compress vortex veins, leading to choroidal effusion.
Key Terms & Definitions
- Ophthalmic artery — main arterial supply to the orbit, branch of internal carotid.
- Central retinal artery — supplies inner retina; first branch of ophthalmic artery.
- Cilioretinal artery — branch of ciliary circulation that can supply the macula.
- Short posterior ciliary arteries — supply choroid and outer retina, form circle of Zinn-Haller.
- Long posterior ciliary arteries — join anterior ciliary arteries at the major arterial circle of iris.
- Vortex veins — main venous drainage of the choroid.
- Anterior segment ischemia — inadequate blood to front eye structures, often surgical complication.
Action Items / Next Steps
- Review anatomy of iris, ciliary body, and choroid for better understanding.
- Watch linked videos on optic nerve and conjunctiva blood supply as suggested.
- Remember clinical implications of artery occlusions and their classic signs.