In a TCD evaluation through the transorbital window, what vessel is being interrogated if an antegrade signal is received at a depth of 50 mm?

In a transorbital Doppler ultrasound evaluation, the target vessel identified at a depth of 50 mm is the ophthalmic artery. The ophthalmic artery typically resides at a depth of approximately 40 to 60 mm when assessed via the transorbital window, which gives rise to measurements corresponding to an antegrade signal. This antegrade flow indicates that the blood is flowing towards the probe, which is characteristic for the ophthalmic artery as it branches from the internal carotid artery and supplies parts of the eye and surrounding structures.

The central retinal artery, while also important in ocular circulation, is usually located deeper around 60 mm and may not consistently produce an identifiable antegrade signal. The superficial temporal artery is located at a much shallower depth of about 10 mm and is assessed using a different approach, typically not through the transorbital window. Lastly, the anterior choroidal artery has a more variable and generally deeper location also precluding it from being discernible at the stated depth as it has a more complex route compared to the ophthalmic artery. Thus, identifying an antegrade signal specifically indicates blood flow within the ophthalmic artery at that depth, confirming it as the vessel being interrogated in this particular scenario.