Blood supply to the face: facial artery anatomy
How the facial arteries are arranged, why the external and internal carotid systems meet around the eye, and what that anastomosis means for injectable safety.
Facial vascular anatomy matters in aesthetic practice for one blunt reason: the arteries of the face are not a closed system. The external carotid supply and the internal carotid supply meet, and material introduced into a branch of one can reach territory belonging to the other. The serious injectable complications described in the literature follow from that single anatomical fact.
The two supplies
The face is served principally by the facial artery, a branch of the external carotid. It crosses the mandible at the anterior border of the masseter, runs a tortuous course toward the nose, and continues as the angular artery alongside the nasal sidewall toward the medial canthus.
The internal carotid supplies the orbit through the ophthalmic artery, whose terminal branches — the supratrochlear and supraorbital arteries — emerge at the superior orbital rim and run upward into the forehead and glabella.
At the medial canthus these territories meet: the angular artery anastomoses with the dorsal nasal branch of the ophthalmic artery. In vascular terms the glabella, nasal dorsum and medial canthus form a junction between an external carotid supply and an internal carotid supply, with the eye sitting on the internal side of that junction.
Why the anastomosis is the whole problem
Injected material that enters an artery travels with the flow. If plunger pressure exceeds arterial pressure, flow in that vessel can be reversed for the duration of the injection — filler moves backwards along the artery, past the branch point. When the pressure stops, normal flow resumes and carries the material forward into whichever branch it now sits closest to.
Where that branch point is the medial canthal anastomosis, the destination can be the ophthalmic artery and its retinal branch. That is the mechanism behind the reported cases of vision loss after cosmetic filler injection — not an idiosyncratic reaction, but a plumbing problem.
Where the reported cases cluster
The published case series identify the same regions repeatedly. In the review by Beleznay and colleagues on blindness caused by cosmetic filler injection (PubMed 25415089) , the distribution of reported cases falls out as:
| Region | Share of reported cases |
|---|---|
| Glabella | 38.8% |
| Nasal region | 25.5% |
| Nasolabial fold | 13.3% |
| Forehead | 12.2% |
The same literature is explicit that this ranking does not describe a safe remainder: there is no absolute safe area of the face to inject. Autologous fat is the filler most frequently implicated in reported blindness; partial visual recovery has been described in some hyaluronic acid and calcium hydroxylapatite cases, but irreversible loss is the common outcome.
Volume and the size of the vessel
An argument that has changed practice is the volume one: the supratrochlear artery, from the glabella to the orbital apex, holds roughly 0.085 mL (reported range 0.04–0.12 mL). A bolus larger than that at a critical point has, in principle, enough material to fill the vessel and reach the orbit. This is the arithmetic behind small-aliquot technique, and it is a more useful constraint than any general instruction to “inject carefully”.
Where retinal artery occlusion does occur, the literature describes a window of roughly 60 to 90 minutes before the loss becomes irreversible — which is why management protocols and hyaluronidase are prepared before the first injection rather than sought afterwards.
Depth is not a reliable shield
A common simplification holds that supraperiosteal placement is safe because named arteries run superficially. Cadaveric work does not support treating that as a rule. In the forehead and glabella the supratrochlear artery becomes progressively more superficial as it ascends, but its course at the orbital rim is deep, and its position varies between individuals and between sides of the same face.
What the anatomy supports is a set of habits rather than a guaranteed plane: know which vessels serve the region, aspirate where the technique allows it, inject slowly and at low pressure, keep each bolus small, keep the needle moving, and prefer a cannula in the regions where the literature reports repeated events.
Variation is the norm
Anatomical studies report substantial variability in the course of the facial artery, and absence or hypoplasia of individual branches is not rare. Textbook diagrams describe a common pattern, not a reliable one. Planning around “where the artery usually is” is planning around a population average that any given patient may not match.
