As mentioned previously, the SOV runs medial to the tendinous insertion of the superior rectus muscle. The SOV then courses diagonally to the lateral border of the superior rectus in the posterior orbit near the annulus of Zinn. The IOV runs just superior to the inferior rectus muscle.[4]

The ophthalmic veins are less well-defined and have more variability than the arteries of the orbit. For example, the diameter of the SOV ranges from 2 to 10 millimeters. Further, the roots of origin and communicating branches vary occasionally and give rise to the medial ophthalmic vein, which is usually unilateral. The IOV shows a much more variable organization. The length of the IOV is inconsistent in the literature, and it drains through a variety of indirect and direct routes.[4]

Carotid-Cavernous Fistula Embolization (Superior Ophthalmic Vein Approach)

Direct cannulation of the SOV is one important approach to the treatment of indirect carotid-cavernous sinus fistulas. The SOV approach may be considered to access these lesions when standard percutaneous coiling techniques are unsuccessful or anatomically challenging. The surgical technique is briefly described as follows.[15][16][17]

After obtaining informed consent, the patient is brought to the angiography suite and placed in the supine position. The upper eyelid is infiltrated with a local anesthetic, and the face is prepped and draped in the usual sterile fashion for oculoplastic surgery. A #15 blade is used to create a skin incision in the upper eyelid crease. A combination of blunt and sharp dissection is carried down through the orbicularis oculi muscle, and the orbital septum is incised with Westcott scissors or monopolar cautery. The pre-aponeurotic fat is dissected until an arterialized feeder vessel of the SOV is visualized, which can be followed to the main trunk of the SOV. The surgeon then bluntly isolates and exposes the SOV and enters the vessel wall with an angiocatheter. After confirming catheter location, standard endovascular techniques, including coiling and injection of liquid embolic agents, are used to obliterate the cavernous sinus. The SOV is then occluded by suture ligation or bipolar cautery unless the vein is too large and thick-walled, in which case, primary closure is necessary.[16][17] Lastly, the skin incision is closed with the surgeon’s choice of suture material.

In rare cases where the traditional approaches fail, including transvenous access by way of the inferior petrosal sinus and direct cannulation of the SOV as described above, percutaneous puncture of the IOV has been shown to be a safe alternative. In this approach, percutaneous access of the IOV is achieved with the aid of ultrasound guidance or advanced imaging techniques.[18][19] Other non-conventional transvenous access techniques have been described, including through the frontal vein, facial vein, pterygoid plexus, inferior petro-occipital vein, and superficial temporal vein.[19][20][21]

Important clinical considerations regarding the ophthalmic veins include the following:

• Carotid-cavernous sinus fistula (CCF): CCF is a rare disorder involving abnormal communication between the cavernous sinus and the carotid arterial system. As the arterial blood flows into the cavernous sinus, the increased pressure causes stasis of venous blood, leading to dilation of the ophthalmic veins—patients present with exophthalmos, ophthalmoplegia, and conjunctival injection. The CCF and dilated ophthalmic veins are viewable on neuroimaging of the orbits. The gold standard for diagnosis and treatment is carotid angiography, although computed tomography angiography is a minimally-invasive alternative for diagnosis only. Treatment via a transarterial approach in direct CCFs is often required to prevent vision loss from elevated intraocular pressure as a result of venous congestion. For indirect CCFs, the preferred treatment is transvenous endovascular embolization. One approach, as outlined above, is the cannulation and ligation of the SOV or IOV under direct visualization.[17][18][22]

• Ophthalmic vein varix: A varix is a rare orbital venous malformation characterized by dilation of thin-walled veins and low blood flow. The inferior ophthalmic venous plexus, in particular, includes many interconnected, narrow valveless veins. Varices are usually present at birth but manifest in young adulthood as diplopia and proptosis during maneuvers that increase venous pressure, such as Valsalva or prone positioning. Over time, there may be paradoxical enophthalmos when the globe retracts as the varix deflates. Imaging, including ultrasound, computed tomography, and magnetic resonance imaging, can be used to detect varices. For symptomatic varices, treatment options include surgical excision with the aid of clips, endovascular coiling, and percutaneous injection of N-butyl cyanoacrylate glue.[23] 

• Increased intracranial pressure: Studies have shown that the diameter of the SOV on imaging correlates directly with intracranial pressure. Isolated bilateral dilation of the SOVs may be the initial sign of increased intracranial pressure, which should prompt urgent evaluation.[24]

• Graves' disease: Color doppler ultrasound has been highlighted in the literature for its use in assessing the SOV in Graves' orbitopathy. During the active phase of thyroid eye disease, there is a significant reduction or reversal in SOV blood flow due to orbital congestion and inflammation. The circulation typically returns to normal following successful treatment, which is supported by clinically and radiographically improved signs of orbital congestion.[25][26]

• Mass effect: Orbital pseudotumor is benign, idiopathic orbital inflammation with no identifiable neoplastic or infectious disorder. The mass effect from orbital edema may compress structures of the orbit, leading to occlusion or constriction of the superior ophthalmic veins, causing venous stasis.[27][28] The most common finding is unilateral dilation of the SOV seen on neuroimaging. This elevated superior ophthalmic venous pressure may increase vascular permeability and decrease venous outflow, even causing choroidal detachment in rare cases.[29]

The ophthalmic veins drain the orbital contents and are the link between the facial and intracranial veins. As such, dilation of the ophthalmic veins is an important clinical consideration. The differential diagnosis for dilated ophthalmic veins is broad, with most common pathologies including carotid-cavernous sinus or dural-cavernous sinus fistulas, venous thrombosis, and facial or orbital arteriovenous malformations.[30]