Ultrasonography is a noninvasive, relatively inexpensive, rapid, office-based technique for imaging the globe, orbit, and carotid arteries. The images are based on the reflection of 8–20 MHz (megahertz) ultrasound waves at acoustic interfaces. One form of ultrasonography, carotid Doppler imaging, is generally accurate at detecting cervical carotid artery stenosis, but it does not provide information about the more proximal or distal vessels. The primary use of carotid Doppler imaging in neuro-ophthalmology is detection of cervical carotid artery stenosis in patients with transient monocular blindness that is suggestive of retinal or optic nerve ischemia. It is not accurate at detecting carotid artery dissection.
Orbital Doppler sonography is useful in the evaluation of a suspected carotid-cavernous fistula by detecting reversal of normally retrograde venous blood flow within the superior ophthalmic vein. Orbital ultrasound provides data concerning the retrobulbar structures, including extraocular muscles, optic nerve, and vessels, but it does not provide accurate imaging of the orbital apex. Ultrasound is also useful for evaluating the optic nerve head (ONH) and can help distinguish ONH edema from ONH drusen; the latter is strongly echogenic (see Chapter 4, Fig 4-22).
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.