Elevated Episcleral Venous Pressure
Episcleral venous pressure (EVP) is an important factor in the determination of IOP. Normal EVP ranges between 6 and 9 mm Hg, depending on the measurement technique used. Elevated EVP may be caused by conditions that either obstruct venous outflow or involve arteriovenous malformations (Table 8-1).
Table 8-1 Causes of Elevated Episcleral Venous Pressure
Patients may note a chronic red eye without ocular discomfort, itching, or discharge. Occasionally, a distant history of a significant head trauma may suggest the cause of a carotid-cavernous sinus (high-flow) fistula or a dural (low-flow) fistula. However, most cases are idiopathic, and some may be familial. Clinically, patients with elevated EVP present with tortuous, dilated episcleral veins (Fig 14-8). These vascular abnormalities may be unilateral or bilateral. Gonioscopy may reveal blood in the Schlemm canal (see Chapter 4, Fig 6-4). In rare instances, signs of ocular ischemia or venous stasis may be present. Sudden, severe carotid-cavernous fistulas may be accompanied by proptosis and other orbital or neurologic signs. Magnetic resonance imaging or angiography to rule out a vascular malformation may be appropriate for these patients. If these tests fail to show an abnormality and the clinical suspicion is high, traditional angiography with neuroradiologic intervention (eg, coiling of fistula) can be considered when the benefits to the patient outweigh the risks.
Figure 8-14 Prominent episcleral vessels in a patient with idiopathic elevated episcleral venous pressure.
(Courtesy of Keith Barton, MD.)
Topical ocular hypotensive medications, particularly those that reduce aqueous production, may be effective in some patients. Because of the etiology of the condition, laser trabeculoplasty is not effective. Glaucoma filtering surgery may be indicated. However, given the risk of a ciliochoroidal effusion or suprachoroidal hemorrhage, prophylactic sclerotomies or scleral windows should be considered.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.