Difference between revisions of "Elevated Episcleral Venous Pressure (EVP)"
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== Surgery ==
== Surgery ==
Surgical intervention should be considered in cases that have not responded first to more conservative efforts. According to several case reports in the literature, uveal effusion-like syndromes have complicated trabeculectomies in elevated EVP and some authors recommend sclerotomies with filtering surgery.<ref name=":1" /><ref>Bhagat N, Lim JI, Minckler DS, Green RL. Posterior uveal effusion syndrome after trabeculectomy in an eye with ocular venous congestion. British Journal of Ophthalmology. 2004 Jan 1;88(1):153-4. </ref> Laser trabeculoplasty has shown not to be beneficial.<ref name=":0" /> One case report recommends performing a "tight" trabeculectomy with multiple releasable sutures to titrate the IOP gradually and prevent anterior chamber
Surgical intervention should be considered in cases that have not responded first to more conservative efforts. According to several case reports in the literature, uveal effusion-like syndromes have complicated trabeculectomies in elevated EVP and some authors recommend sclerotomies with filtering surgery.<ref name=":1" /><ref>Bhagat N, Lim JI, Minckler DS, Green RL. Posterior uveal effusion syndrome after trabeculectomy in an eye with ocular venous congestion. British Journal of Ophthalmology. 2004 Jan 1;88(1):153-4. </ref> Laser trabeculoplasty has shown not to be beneficial.<ref name=":0" /> One case report recommends performing a "tight" trabeculectomy with multiple releasable sutures to titrate the IOP gradually and prevent anterior chamber during surgery.<ref>Pradhan ZS, Kuruvilla A, Jacob P. Surgical management of glaucoma secondary to idiopathic elevated episcleral venous pressure. Oman Journal of Ophthalmology. 2015 May;8(2):120.</ref>
== Follow up ==
== Follow up ==
Revision as of 21:41, June 17, 2017
Elevated episcleral venous pressure (EVP) is a clinical finding which may be observed in a variety of primary conditions. It can also bean be idiopathic, although this is a diagnosis of exclusion. In either case, elevated EVP may be associated with elevated intraocular pressure (IOP) and glaucoma. Idiopathic elevated EVP leading to secondary open angle glaucoma is also known as Radius-Maumenee syndrome in German literature.
Average EVP ranges from 8-10 mmHg, although it can transiently elevate with downward displacement of the head. Persistently elevated EVP is a known cause of open-angle glaucoma as it can lead to obstruction of the aqueous drainage into the orbital venous system. If not caught early it can lead to an insidious onset of glaucoma and subsequent vision loss. Idiopathic elevated EVP was first described in 1968 by Thomas Minas and Steven Podos in a case report of a family with two members found to have the condition after ruling out primary entities known to cause secondary elevated EVP.
The Goldmann equation describes intraocular pressure (IOP) as the rate of aqueous humor production divided by the facility of outflow plus EVP. In the acute setting, IOP rises 1 mmHg for every 1 mmHg increase in EVP. However, the relationship between IOP and elevated EVP in chronic conditions is less well understood. Chronically elevated EVP can cause blood to reflux into Schlemm’s canal, which can decrease the facility of outflow of aqueous into the trabecular meshwork and subsequently raise the IOP.
Etiologies leading to elevated EVP are numerous and can be divided into several subcategories including venous obstruction, arteriovenous anomalies, and idiopathic pathologies. Patients may endorse a distant history of craniofacial trauma that might suggest the cause of a carotid cavernous sinus, dural fistula, or other arteriovenous anomaly. Potential causes of elevated EV include:
- Venous Obstruction
- Retrobulbar tumor
- Orbital amyloidosis
- Thyroid ophthalmopathy
- Jugular vein obstruction
- Congestive heart failure
- Thrombosis of cavernous sinus or orbital vein
- Vasculitis involving episcleral vein or orbital vein
- Superior vena cava syndrome (mediastinal tumor)
- Arteriovenous Anomalies
- Carotid-cavernous sinus fistula
- Orbital varix
- Sturge–Weber syndrome
- Orbital–meningeal shunts
- Carotid–jugular venous shunts
- Intraocular vascular shunts
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.
Branches of the anterior ciliary venous circulation system anastomose with efferent channels of the canal of Schlemm before converging with the episcleral venous plexus of Tenon's capsule and the conjunctiva. With very few capillary networks present in the angioarchitecture of the episcleral vessels, arteriovenous vasculature anastomoses predominate. The episcleral venous plexus will ultimately drain into the ophthalmic veins, which then drain into the cavernous sinus.
Increased venous pressure downstream to the episcleral anastomoses leads to decreased outflow of venous blood from the orbit and decreased outflow of aqueous. A subsequent pressure difference across the trabecular meshwork occurs, lowering aqueous egress. Elevated EVP resulting in chronic IOP elevations can then lead to glaucomatous damage and the eventual diagnosis of secondary open angle glaucoma.
Patients with elevated EVP may be entirely unaware of their condition or the underlying cause. They generally present without typical glaucomatous signs or symptoms early in their disease. Patients may endorse a distant history of craniofacial trauma that might suggest the cause of a carotid cavernous sinus, dural fistula or any other arteriovenous anomaly. It is important to review the patient’s medical history, particularly for conditions such as amyloidosis, hyperthyroidism, congestive heart failure, hypercoagulable states, vasculitis, superior vena cava syndrome, Sturge–Weber syndrome, or other arteriovenous anomalies which may suggest an underlying cause for the elevated EVP.
A clinical diagnosis of elevated EVP can be suspected when a patient presents with chronically injected episcleral vessels without a history of pain or irritation (Fig. 1). Elevated EVP can lead to small concentrations of blood reflux seen in Schlemm’s canal on gonioscopy. Hyalinization of the inner wall of Schlemm’s canal can occur secondary to this chronic accumulation of blood in the canal.Cite error: Closing
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<ref> tag It should be noted that blood in Schlemm’s canal, hyalinization of the inner wall, and neovascularization of the iris are all not specific for elevated EVP, but one should have raised suspicions of elevated EVP should they occur. It is of particular importance to be suspicious of elevated EVP in patients with unilateral dilated episcleral vessels. Elevated EVP can be present bilaterally, but most commonly presents unilaterally as the condition is commonly a sequela of ipsilateral localized anatomical variants.
Other physical exam findings include chemosis, proptosis, and an orbital bruit. However, these are less reliable findings and their presence can depend on the underlying conditions leading to elevated EVP. Pulsatile exophthalmos may be seen when elevated EVP is associated with a carotid-cavernous fistula. In elevated EVP, glaucomatous optic atrophy and visual field loss can be more insidious than other acute forms of glaucoma.
Elevated EVP is often the result of another underlying disorder. A complete workup of the patient with elevated EVP to rule out underlying causes may include ultrasound biomicroscopy, orbital ultrasonography, computerized axial tomography, magnetic resonance imaging, chest x-ray and angiography. Only after this workup is completed and negative may the patient be considered to have idiopathic elevated EVP.
There are several different diagnostic modalities which may be used to measure the EVP, though many of these are not routinely performed clinically. These include one direct method (cannulation), and three indirect methods (venomanometer pressure chamber, torsion balance, and air jet). The most accurate of these is direct cannulation, and the most accurate form of the indirect method is venomanometer. Other investigators have also used color-coded Doppler sonography to measure blood pulsation from the ophthalmic veins.
Direct Cannulation. This method includes insertion of a cannula into an episcleral vein. These veins range in diameter from 50-100 micrometers, and investigators have used two different cannulation methods: complete and partial vessel occlusion. In the complete occlusion method, plastic tubing is employed to occlude an episcleral vessel completely. In the partial vessel occlusion method, a glass pipette with a beveled 2-5 micrometer tip is placed in the episcleral vessel. For best measurements, the cannula must face downstream.
Venomanometer Pressure Chamber. In short, the venomanometer pressure chamber method requires a particular apparatus to be attached to the slit lamp with a chamber consisting of an encased, highly distensible and transparent membrane, which is applied to the conjunctiva at a preselected episcleral vessel. The pressure within the chamber is slowly increased until a subjective endpoint of a collapsed episcleral vein is observed. Several membranes have been utilized in this technique including latex, serosal membrane, frog pericardium, and silicone rubber. This is the most common non-invasive method for determining EVP in part due to its commercial availability (marketed as Episcleral Venomanometer, Model EV-310, EyeTech Ltd, Morton Grove, IL).
Torsion Balance. This method requires a particular torsion balance instrument (very similar to the Goldmann applanation tonometer) to be mounted to the slit lamp. The applanation surface of the instrument has a diameter of 300 micrometers and is placed directly on the conjunctiva. Magnification is set at 25 to 40X and force is applied until a subjective endpoint of a collapsed episcleral vein is observed. Being that the area of the applanation surface is fixed, EVP can be determined by the force required to collapse the vessel.
Air Jet. Similar to the venomanometer and torsion balance methods, the air jet also utilizes a subjective endpoint of a collapsed episcleral vein by an applied pressure in this case administered via an air jet.
There is currently no laboratory test routinely used to suggest a patient has elevated EVP. Lab testing may be used as needed to evaluate for any underlying conditions.
The differential diagnosis for elevated EVP includes entities that present with prominent ocular vessels. Elevated EVP tends to present with larger caliber, more tortuous vessels than many of the following etiologies. Other differential diagnosis for a chronically injected eye includes:
- Ataxia telangiectasia
- Acute closed angle glaucoma
- Episcleral nodule
- Cornea lesion near the limbus
- Foreign body
- Herpetic keratitis
- Uveal neoplasm
- Polycythemia vera
The management of elevated EVP can be medical or surgical. Care should be taken first to address any primary medical condition that might have caused the elevated EVP and would require specific treatment.
Medical management of elevated IOP and secondary glaucoma due to elevatedEVP includes inhibiting aqueous production via beta-blockers and carbonic anhydrase inhibitor. Apraclonidine may also be considered due to its arterial vasoconstriction effects leading to less blood flow to the eye.
Surgical intervention should be considered in cases that have not responded first to more conservative efforts. According to several case reports in the literature, uveal effusion-like syndromes have complicated trabeculectomies in elevated EVP and some authors recommend sclerotomies with filtering surgery. Laser trabeculoplasty has shown not to be beneficial. One case report recommends performing a "tight" trabeculectomy with multiple releasable sutures to titrate the IOP gradually and prevent anterior chamber shallowing during surgery.
Follow up of elevated EVP may depend upon the underlying cause, but otherwise is similar to that of other glaucomatous conditions. Patients should undergo routine follow-up assessing visual acuity, IOP, gonioscopy, visual fields, OCT, and DFE and EVP with appropriate referral as necessary for any additional underlying condition.
A major complication of untreated elevated EVP is secondary open angle glaucoma. Elevated EVP can also lead to acute angle-closure glaucoma because venous stasis in the vortex veins can cause serous choroidal detachment or suprachoroidal hemorrhage leading to the forward displacement of the lens-iris diaphragm. Neovascular glaucoma has also been reported as a complication of elevated EVP once arterial blood flow has met enough IOP resistance to cause ocular ischemia.
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