Fundus Examination
Slit-lamp microscopy: Identifies tortuous looped vessels on the optic disc.
RAPD (Relative Afferent Pupillary Defect): Correlates with the degree of ischemia and is useful for determining the ischemic type of CRVO 1).
Opticociliary Shunt Vessels
Key Points at a Glance
Section titled “Key Points at a Glance”1. What are Optociliary Shunt Vessels?
Section titled “1. What are Optociliary Shunt Vessels?”Optociliary shunt vessels are collateral vessels formed on the optic disc. They connect the retinal venous system with the choroidal venous system (peripapillary choroidal veins), diverting blood from the retina to the vortex veins and ophthalmic venous system. They are also called optociliary collateral vessels.
Congenital shunt vessels are extremely rare; most are acquired. They result from chronic retinal venous stasis, leading to dilation and development of pre-existing anastomotic capillary channels.
Q
Are there congenital shunt vessels?
A
Congenital shunt vessels exist but are extremely rare. Most are acquired and form as a result of underlying diseases that cause chronic retinal venous stasis.
2. Main Symptoms and Clinical Findings
Section titled “2. Main Symptoms and Clinical Findings”Subjective Symptoms
Section titled “Subjective Symptoms”Shunt vessels themselves do not cause symptoms. All symptoms reported by patients are due to the underlying disease.
- Vision loss: Due to underlying diseases such as CRVO or optic nerve sheath meningioma.
- Visual field defects: Associated with optic nerve compression or retinal ischemia.
- Asymptomatic: Shunt vessels may be discovered incidentally during fundus examination.
Clinical Findings
Section titled “Clinical Findings”Observed as tortuous vascular loops on the optic disc. The number of visible loops ranges from one to several, arising from the disc margin and winding.
The most important clinical challenge is differentiation from neovascularization of the disc (NVD). It is distinguished from disc neovascularization by the following features.
| Finding | Shunt Vessel | Disc Neovascularization (NVD) |
|---|---|---|
| Course | Loop-like, tortuous | Fine vascular network |
| Caliber | Relatively thick | Thin and irregular |
| FA Leakage | None | Present (marked) |
Optic nerve sheath meningioma presents with the triad of shunt vessels, visual loss, and optic atrophy (Hoyt-Spencer sign). Shunt vessels are observed in about 60% of optic nerve sheath meningiomas.
Q
How to differentiate between optic disc neovascularization and shunt vessels?
A
The most reliable method of differentiation is fluorescein angiography (FA). Shunt vessels do not show leakage of fluorescein dye, whereas optic disc neovascularization shows marked leakage. In addition, shunt vessels have a larger diameter than optic disc neovascularization and exhibit a loop-like course.
3. Causes and Risk Factors
Section titled “3. Causes and Risk Factors”Chronic retinal venous outflow obstruction is a prerequisite for the formation of shunt vessels. The causative diseases are as follows.
Diseases that chronically cause venous stasis at the optic disc are responsible.
| Frequency | Causative Disease |
|---|---|
| Common | CRVO, optic nerve sheath meningioma |
| Rare | Chronic glaucoma, optic disc drusen, optic glioma, pseudotumor cerebri |
CRVO (central retinal vein occlusion) is the most common cause. Retinal vein occlusion (RVO) is the second most common retinal vascular disease after diabetic retinopathy, with hypertension, diabetes, and glaucoma being major risk factors 1). Iris neovascularization occurs in 25% of CRVO patients 1).
Optic nerve sheath meningioma accounts for 1–2% of all meningiomas and about 10% of all orbital tumors. A meningioma arising in the retrobulbar region compresses the central retinal vein, causing chronic venous stasis.
4. Diagnosis and Examination Methods
Section titled “4. Diagnosis and Examination Methods”Diagnosis of shunt vessels is based on fundus examination and confirmed/evaluated by multiple imaging tests.
FA/ICG Angiography
Fluorescein angiography (FA): Confirms the absence of dye leakage from shunt vessels. It is essential for differentiation from optic disc neovascularization.
ICG angiography: Can visualize blood flow patterns from the choroidal circulation to the vortex veins and ophthalmic veins.
OCTA/Imaging Tests
OCTA (Optical Coherence Tomography Angiography): Non-invasively confirms blood flow in shunt vessels.
CT/MRI: In optic nerve sheath meningioma, the tram-track sign (thickening of the optic nerve sheath with calcification) is a characteristic finding.
5. Standard Treatment
Section titled “5. Standard Treatment”Shunt vessels themselves do not require treatment. They function as protective collateral circulation, and removing or occluding them is contraindicated. Treatment is directed at the underlying disease.
Treatment of CRVO
Anti-VEGF therapy (first-line): Ranibizumab, aflibercept, faricimab, and bevacizumab are used. Repeated intravitreal injections are the standard 1).
Steroids: Triamcinolone and dexamethasone implants are also used, but due to risks of elevated intraocular pressure and cataracts, they are considered second-line 1).
Treatment of Meningioma
Stereotactic radiotherapy: This is the standard treatment for optic nerve sheath meningioma. Regression of shunt vessels after treatment has been reported.
Observation: In cases with slow progression, regular monitoring may be chosen.
Increased Intracranial Pressure
Optic nerve sheath fenestration: For shunt vessels associated with pseudotumor cerebri (idiopathic intracranial hypertension), regression after optic nerve sheath fenestration has been reported.
Medical treatment: Management with intracranial pressure-lowering drugs such as acetazolamide is also performed.
Q
Do shunt vessels need to be treated?
A
Shunt vessels themselves do not require treatment. They play a protective role by diverting venous blood from the retina to the choroid, and blocking them would be harmful. The focus of management should always be on treating the underlying disease.
6. Pathophysiology and Detailed Mechanism
Section titled “6. Pathophysiology and Detailed Mechanism”Normal Retinal Venous Blood Flow
Section titled “Normal Retinal Venous Blood Flow”Under physiological conditions, the central retinal vein collects venous blood from the retina and drains into the cavernous sinus via the superior ophthalmic vein. Blood supply to the optic disc is provided by the short posterior ciliary arteries, which perfuse the prelaminar region 2).
Mechanism of shunt vessel formation
Section titled “Mechanism of shunt vessel formation”When chronic occlusion or compression is applied to the central retinal vein, collateral channels develop between the peripapillary choroidal veins in the prelaminar region.
- Dilation of pre-existing anastomoses: Even in healthy eyes, fine anastomotic channels exist in the prelaminar region. Chronic venous stasis creates a pressure gradient, causing these channels to dilate and open.
- Formation of a bypass route: Through the dilated collateral channels, retinal venous blood flows into the choroidal veins and is drained via the vortex veins into the ophthalmic veins. ICG angiography shows outflow from the choroidal circulation to the vortex veins.
Mechanism in optic nerve sheath meningioma
Section titled “Mechanism in optic nerve sheath meningioma”A meningioma arising in the retrobulbar region compresses the central retinal vein from the outside, leading to chronic venous stasis. Even as optic atrophy progresses, some visual acuity may be preserved, which is thought to be due to improved venous drainage via shunt vessels. After CRVO, improved venous drainage through collateral vessels also contributes to visual recovery 1).
Q
Can shunt vessels disappear?
A
Cases have been reported in which shunt vessels regress after treatment of the underlying disease. Regression has been observed after stereotactic radiotherapy for optic nerve sheath meningioma and after optic nerve sheath fenestration for pseudotumor cerebri. However, regression cannot be expected in all cases.
7. Latest research and future perspectives (reports under investigation)
Section titled “7. Latest research and future perspectives (reports under investigation)”Large-scale clinical trials for CRVO treatment
Section titled “Large-scale clinical trials for CRVO treatment”The efficacy of anti-VEGF therapy for CRVO has been demonstrated in multiple large-scale RCTs.
In the COPERNICUS and GALILEO trials, 56% of patients who received intravitreal aflibercept achieved a gain of 15 or more letters in visual acuity at 24 weeks (vs. 12% in the placebo group) 1).
In the CRUISE study, the ranibizumab 0.5 mg group achieved a mean visual acuity improvement of 14.9 letters from baseline at 6 months, significantly outperforming the sham injection group (0.8 letters improvement) 1). This is important evidence supporting the efficacy of anti-VEGF therapy for CRVO.
Long-term data from BVOS show that 37% of CRVO patients experience spontaneous visual improvement of 2 lines or more, with 34% achieving final visual acuity of 20/40 or better, and 23% remaining at 20/200 or worse 1).
Prognostic Value of Shunt Vessels
Section titled “Prognostic Value of Shunt Vessels”Whether the presence of shunt vessels predicts CRVO prognosis remains a topic of debate. It has been suggested that cases able to form shunt vessels may have relatively better prognosis because venous drainage is preserved to some extent, but established evidence is still lacking.
8. References
Section titled “8. References”- AAO Retina/Vitreous Panel. Retinal Vein Occlusions Preferred Practice Pattern. Ophthalmology. 2024.
- Salvetat ML, Pellegrini F, Spadea L, et al. Non-Arteritic Anterior Ischemic Optic Neuropathy: A Comprehensive Review. Vision. 2023;7(4):72.