Elevated Episcleral Venous Pressure (EVP)
Elevated episcleral venous pressure (EVP) is a clinical finding which may be associated with elevated intraocular pressure (IOP) and glaucoma if left chronically untreated. In many cases the diagnosis is secondary to an underlying etiology, however it can also be idiopathic if all other causes are excluded. The idiopathic form can be familial or sporadic. In German literature idiopathic elevated EVP leading to secondary open angle glaucoma has been termed Radius-Maumenee Syndrome.
Based on the Goldmann equation, intraocular pressure (IOP) is the rate of aqueous humor production divided by the facility of outflow plus EVP. The average EVP ranges from 8-10 mmHg, although can transiently change based on head positioning. In the acute setting, there is a linear relationship and 1 mmHg rise in EVP correlates to a 1 mmHg rise in IOP. However, this relationship is not as well understood in chronic cases.
In the conventional drainage pathway, aqueous humor flows through the efferent channels of the canal of Schlemm and then through the anterior ciliary venous circulation before converging with the episcleral venous plexus at Tenon’s capsule and the conjunctiva. Given the paucity of capillary networks in episcleral vessels, arteriovenous vasculature anastomosis predominate. The aqueous in the episcleral venous plexus will then drain into the superior ophthalmic vein and enters the cavernous sinus above the annulus of Zinn, before flowing into the internal jugular vein and into the right atrium via the superior vena cava. Any obstruction along this pathway may cause elevated EVP.
If there is increased venous pressure downstream to the episcleral anastomoses, then there is subsequent decrease in outflow of blood from the orbit and aqueous. Thus, in chronic cases, elevated EVP can cause blood reflux into Schlemm’s canal. This can subsequently raise IOP chronically, which can lead to glaucomatous damage due to secondary open angle glaucoma.
Etiologies can range from venous obstruction to arteriovenous anomalies and can be acute or chronic in nature. It is important to elicit the timing of any trauma and do a full review of systems, including any previous infectious exposures, to rule out life or vision threatening causes of elevated EVP.
Jugular Vein Obstruction
Congestive Heart Failure
Thrombosis of cavernous sinus or orbital vein
Vasculitis involving episcleral or orbital vein
Superior Vena Cava Syndrome (Mediastinal Tumor)
Carotid-Cavernous Sinus Fistula (acute vs. chronic)
Any history of head trauma is a risk factor for developing a carotid cavernous sinus, dural fistula or other arteriovenous anomaly which can lead to the development of elevated EVP.
Typically, when patients present for evaluation of elevated EVP it is due to chronic eye redness that has not responded to previous treatment and often is misdiagnosed as chronic conjunctivitis. They are usually unaware of their condition or underlying cause and typically do no describe pain or irritation. It is important to ask about recent trauma, specifically craniofacial, that can suggest a carotid cavernous sinus (high flow) or dural (low flow) fistula. A complete past medical history should be obtained to rule out etiologies that may cause venous obstruction, including but not limited to hyperthyroidism, amyloidosis, congestive heart failure, hypercoagulable states, vasculitis, superior vena cava syndrome and Sturge-Weber Syndrome.
Clinical exam is the gold standard for diagnosing elevated EVP. Typically, on physical examination, the episclera is injected and demonstrates the pathognomonic corkscrew episcleral vessels without inflammation (Figure 1). It is important to perform gonioscopy, which can show an open angle with blood reflux in Schlemm’s canal or hyalinization of the wall of Schlemm’s canal due to chronic accumulation of blood. Other signs include chemosis, proptosis and the presence of an orbital bruit, however these are specific signs for elevated EVP. If the elevated EVP is secondary to a carotid-cavernous fistula, then pulsatile exophthalmos can sometimes be seen. Intraocular pressure (IOP) can often times be elevated in the affected eye. Ancillary testing would include a optic coherence tomography (OCT) scan and Humphrey Visual Field testing to assess for glaucomatous changes.
· Ataxia Telangiectasia
· Acute Closed Angle Glaucoma
· Episcleral Nodule
· Corneal lesion near limbus
· Foreign body
· Herpetic Keratitis
· Uveal Neoplasm
A complete workout to rule out underlying etiology should be done when elevated EVP is suspected. In the setting of detecting an arteriovenous fistula, cerebral angiography is the gold standard, however orbital Doppler ultrasound is a non-invasive method which can confirm dilation of the superior ophthalmic vein. Other modalities for diagnosis include orbital ultrasound, ultrasound biomicroscopy (UBM), computerized axial tomography and magnetic resonance imaging.
There are diagnostic modalities that measure EVP however are not routinely used in clinical practice. Direct cannulation is a direct method and can be done with the complete occlusion or partial vessel occlusion method; this is the most accurate test. Indirect methods include the venomanometer pressure chamber, torsion balance and air jet. Of the indirect methods the venomanometer is the most accurate.
The aim of management should revolve around first treating the primary underlying etiology. If no etiology is determined for the elevated EVP then treatment is similar to that of primary open angle glaucoma (POAG).
Medical therapy is aimed at decreasing aqueous humor production and increasing uveoscleral outflow. Medications that enhance outflow through the conventional pathway are not as effective. Beta blockers and carbonic anhydrase inhibitors are favored in treatment of elevated EVP. Given its action on the arterial vasculature, Apraclonidine may be considered as it decreases blood flow to the eye.
Surgical therapy should be considered if patients are refractory to medical therapy. Again, aim should be to bypass the trabecular outflow, therefore selective laser trabeculoplasty (SLT) and micro-pulse laser trabeculoplasty (MLT) are not recommended. Trabeculectomy and sclerotomy are appropriate surgical options. Eyes with elevated EVP have been reported to be at higher risk for uveal effusion syndrome. Therefore, special consideration is needed to prevent hypotony during surgery. Prophylactic sclerotomies or scleral windows may be necessary. One case recommends a surgical technique where a tight trabeculectomy with multiple adjustable sutures, the sutures can then be used to titrate the IOP gradually and therefore prevent acute shallowing of the anterior chamber intraoperatively. Other reports suggest maintaining the anterior chamber with injection of balance salt solution and viscoelastic, in addition to adjustable suture placement on the scleral flap. Medical management post operatively can include use of cycloplegic agents and glucocorticoids to reduce inflammation.
The major complication for untreated elevated EVP is development of secondary open angle glaucoma. Elevated EVP can also lead to acute angle closure glaucoma as suprachoroidal hemorrhage with subsequent forward displacement of the lens-iris diaphragm. Rarely, neovascular glaucoma can occur as a result of ocular ischemia.
Follow up for these cases varies depending on the underlying etiology and IOP. If following for secondary open angle glaucoma, frequent follow up is needed with routine IOP checks, gonioscopy, OCT and visual fields to monitor and prevent glaucomatous progression.
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