In collateral flow via ECA to the brain, what happens to ophthalmic artery flow?

• A. Reversed flow
• B. Normal forward flow
• C. No flow
• D. Bidirectional flow

Answer: (C)

The key idea is that external carotid to intracranial collateral flow can use the ophthalmic artery as a bridge. The ophthalmic artery normally arises from the internal carotid and supplies the eye. When collateral blood supply comes from the external carotid system, pressure from those branches can drive blood backward through the ophthalmic artery into intracranial vessels. So the ophthalmic artery flow is reversed relative to its usual direction. On Doppler, you’d expect retrograde flow in the ophthalmic artery as part of this collateral pattern. In some situations, flow may appear bidirectional depending on exact pressure gradients, but the classic finding is reversed flow.