Optic Nerve Sheath Decompression

Key Points at a Glance

Optic nerve sheath decompression (ONSD/ONSF) is a surgical procedure that creates a slit or window in the optic nerve dura to drain cerebrospinal fluid (CSF) and relieve compression on the optic nerve.
The most common indication is idiopathic intracranial hypertension (IIH), performed in cases of vision loss resistant to medical treatment.
A meta-analysis (19 studies, 1159 observations) reported visual acuity improvement in 41%, visual field improvement in 76%, and papilledema improvement in 97%.
It has been confirmed that unilateral surgery can improve contralateral papilledema, and some reports show bilateral effects in all cases.
This procedure does not lower intracranial pressure (ICP) itself; its main purpose is vision protection and it is ineffective for headache treatment.
Surgical delay beyond 6 months from diagnosis is associated with worse visual field outcomes, and early intervention is recommended.
After optic atrophy has occurred, visual recovery with ONSF is limited.

1. What is Optic Nerve Sheath Decompression?

Optic nerve sheath decompression (ONSD), also called optic nerve sheath fenestration (ONSF), refers to the same surgical procedure. A slit or window (fenestration) is created in the dura mater surrounding the optic nerve, allowing CSF from the subarachnoid space to drain, thereby locally reducing pressure on the optic nerve. CPT code 67570 is assigned.

The most common indication is idiopathic intracranial hypertension (IIH), with about 25% of cases refractory to medical treatment requiring surgical intervention. Other indications may include cerebral venous sinus thrombosis, cryptococcal meningitis, all-trans retinoic acid (ATRA)-induced pseudotumor cerebri¹⁾, and moyamoya disease⁴⁾.

Epidemiology (IIH): The annual incidence of IIH in the United States is 1.15 per 100,000. It is higher in women (1.97 per 100,000) than in men (0.36 per 100,000), with the highest rate in those aged 18–44 years (2.47 per 100,000). The prevalence of IIH is rising with the global increase in obesity.

Historical Background

Year	Event
1853	Turck and Coccius first report papilledema
1872	De Wecker first reports ONSD (as treatment for neuroretinitis)
1964	Hayreh demonstrated resolution of papilledema after optic nerve sheath fenestration
1973	Galbraith & Sullivan developed the medial transconjunctival approach
1988	Tse et al. extended the lateral orbital approach
2001	Pelton & Patel reported the superomedial eyelid crease approach

Q Are optic nerve sheath decompression and optic nerve sheath fenestration different surgeries?

Both refer to the same surgical procedure. The difference is only in terminology; both involve creating a slit or window in the optic nerve dura to drain CSF. The confusion arises because the English terms ONSD (optic nerve sheath decompression) and ONSF (optic nerve sheath fenestration) are translated into Japanese as “decompression surgery” and “fenestration surgery,” respectively.

2. Main Symptoms and Clinical Findings

optic nerve sheath decompression bilateral disc edema

Papilledema With Intracranial Hypertension and Ectopic Orbital Calcification During Hemodialysis: A Case Report. Cureus.; 17(3):e80284. Figure 1. PMCID: PMC11977438. License: CC BY.

(A) Fundus photography at the initial visit showing optic disc swelling and redness in both eyes; (B) Autofluorescence showing no signs of optic disc drusen

Subjective Symptoms

Intracranial hypertension (especially IIH) indicated for ONSD presents with the following symptoms.

Headache: Typically a positional throbbing headache. It can interfere with daily activities.
Transient visual obscurations: Brief vision loss lasting seconds, occurring with position changes. Characteristic of IIH.
Pulsatile tinnitus: Tinnitus synchronized with the heartbeat. A characteristic symptom of intracranial hypertension.
Decreased visual acuity: Subjective vision loss. In IIH, it is mild initially but becomes pronounced as the disease progresses.
Horizontal diplopia: Double vision in the horizontal direction due to abducens nerve palsy.
Photopsia and retro-orbital pain: Discomfort or flashes of light in the orbit.

Clinical Findings (Findings Confirmed by Physician Examination)

Papilledema: The most important finding in IIH. Typically, bilateral optic disc swelling is observed.
Abducens nerve (sixth cranial nerve) palsy: A false localizing sign of increased intracranial pressure. Causes esotropia and horizontal diplopia.
RAPD (Relative Afferent Pupillary Defect): Positive when optic neuropathy is asymmetric. In ATRA-induced pseudotumor cerebri cases, RAPD in the right eye has been confirmed¹⁾.
Visual field abnormalities: Enlargement of the physiological blind spot is an early finding. As it progresses, peripheral visual field constriction and generalized sensitivity loss appear.
Optical coherence tomography (OCT) findings: Thickening of the peripapillary retinal nerve fiber layer (pRNFL). In severe cases, it may exceed 300 μm¹⁾.

Characteristics of fulminant IIH: Rapid vision loss within weeks, pRNFL >300 μm, and mean CSF opening pressure on first lumbar puncture of 54.1 cm H₂O (range 29–70) are characteristic. Visual recovery is poor when the Humphrey visual field mean deviation is < -7 dB.

3. Causes and Risk Factors

The most common risk factors for IIH, for which ONSF is most frequently performed, are listed below.

Obesity: The greatest risk factor. Even a 5–10% weight loss can lead to significant symptom improvement.
Female sex and young age: Overwhelmingly more common in women (female:male ≈ 5:1), with peak incidence between 18 and 44 years.
Endocrine disorders: Conditions such as Addison’s disease and polycystic ovary syndrome (PCOS) are involved.
Drug-induced: Vitamin A and retinoids (including ATRA ¹⁾), tetracyclines, growth hormone, and steroid withdrawal can be triggers.
Race: Highest in Black individuals (2.05/100,000) > White (1.04) > Hispanic (0.67) > Asian/Pacific Islander (0.16).
Anemia: Iron deficiency anemia has been reported to be associated with IIH.
Genetic factors: Candidate regions have been identified on chromosomes 5, 13, and 14, but no Mendelian inheritance pattern has been established.

ONSF may also be indicated for other causes of increased intracranial pressure (such as moyamoya disease ⁴⁾, cerebral venous sinus thrombosis, infections, and space-occupying lesions).

Q Are there diseases other than IIH for which optic nerve sheath decompression is performed?

In addition to IIH, indications may include cerebral venous sinus thrombosis, cryptococcal meningitis, increased intracranial pressure associated with moyamoya disease, and ATRA (all-trans retinoic acid)-induced pseudotumor cerebri syndrome. In cases of moyamoya disease, ONSF has been performed for refractory increased intracranial pressure, with reports of visual recovery.

4. Diagnosis and Examination Methods

IIH Diagnostic Criteria (Modified Dandy Criteria)

All of the following items must be met.

Symptoms of increased intracranial pressure (headache, nausea, transient visual obscurations, papilledema)
No focal neurological signs except abducens nerve palsy
Patient is awake and alert
Normal CT/MRI findings (including exclusion of venous sinus thrombosis)
Lumbar puncture opening pressure >250 mm H₂O (adults), normal CSF composition
No other cause of increased intracranial pressure

Main diagnostic tests

Fundus examination: Assessment of presence and degree of papilledema. Grading using the Frisén classification is useful.
Visual field testing (Humphrey automated perimetry): Enlarged blind spot, peripheral visual field constriction, generalized sensitivity reduction. Also serves as an indicator for follow-up.
OCT: Quantitative assessment of pRNFL thickness. Useful as a severity indicator and for follow-up.
Brain MRI/MRV: Exclusion of space-occupying lesions, hydrocephalus, and venous sinus thrombosis. Characteristic findings in IIH include empty sella, transverse sinus stenosis, optic nerve sheath distension, and posterior scleral flattening.
Lumbar puncture: Measurement of opening pressure (≥250 mm H₂O) and confirmation of CSF composition. Also serves as a temporary therapeutic measure at the time of diagnosis.
Fluorescein fundus angiography: Useful for differentiating papilledema from optic disc drusen.

Differential diagnosis: Venous sinus thrombosis, anemia, obstructive sleep apnea, drug-induced (tetracyclines, vitamin A, etc.), endocrine abnormalities. When accompanied by acute visual loss, differentiation from malignant hypertension, meningitis, optic neuritis (MOG, NMOSD, etc.), and optic nerve infiltration (leukemia, lymphoma) is important.

5. Standard treatment

Medical Treatment (First-Line)

Weight loss: The most important disease-modifying therapy. A 5–10% weight reduction can significantly improve papilledema and visual field. Combination with a low-sodium weight-loss diet is recommended.
Acetazolamide: First-line drug (carbonic anhydrase inhibitor). Reduces CSF production and lowers ICP. In fulminant cases, start at 500 mg three times daily and may be rapidly titrated up to 3–4 g/day.
Topiramate: Alternative when acetazolamide is not tolerated. Lowers ICP and improves visual function.
Furosemide: Diuretic. An adjunctive agent that reduces CSF production.
Intravenous methylprednisolone (1 g/day for 3 days): Used only in fulminant cases. Reported in pediatric cases in North America, but routine use in adult fulminant cases is not recommended in the UK.

Surgical Treatment

Optic Nerve Sheath Decompression (ONSD/ONSF)

Indications: When headache is mild but there is marked papilledema with progressive or threatening vision loss. The main goal is to protect vision; it is ineffective for headache treatment.

Surgical approaches: Three main approaches are used.

Medial transconjunctival

Frequency of use: 59%, the most common.

Advantages: Shortest route. Cosmetically superior.

Disadvantages: Strabismus risk, longer surgery time.

Superomedial eyelid margin incision

Frequency of use: 31%.

Advantages: Shortest surgery time. No microscope needed.

Disadvantages: Longer route, risk of ptosis.

Lateral orbitotomy

Frequency of use: 10%, the least common.

Advantages: Good visualization of the optic nerve.

Disadvantages: Risk of ciliary ganglion injury.

Surgical outcomes (meta-analysis: 19 studies, 1159 observations)³⁾:

Outcome measure	Improvement rate	95% CI
Visual acuity improvement	41.09%	29–55%
Visual field improvement	76.34%	61–87%
Papilledema improvement	97%	84–100%

The visual field improvement rate with the transconjunctival approach (86%) is significantly higher than with other approaches (57%) (p=0.018). There is no significant difference in visual acuity improvement rates between approaches (p=0.715)³⁾.

Bilateral effect from unilateral surgery: Unilateral ONSF also improves contralateral papilledema. In a 2-year follow-up of 9 patients (all female) with idiopathic intracranial hypertension after unilateral ONSF, bilateral visual improvement was confirmed in all cases²⁾.

Complication risk: Overall 10–15%. The most serious complication is vision loss due to central retinal artery occlusion or central retinal vein occlusion (1–2%). Other reported complications include diplopia (22.2%), subconjunctival hemorrhage (44.4%), and orbital cellulitis (11.1%), but these are often transient²⁾.

CSF Shunt Surgery

Lumbar peritoneal shunt (LPS): Widely used as a first-line surgical intervention for idiopathic intracranial hypertension. It lowers ICP and is effective for headache improvement (short-term).
Ventriculoperitoneal shunt (VPS): Effectively lowers ICP. Complications include shunt failure, infection, and migration.

Venous Sinus Stenting (VSS)

Venous sinus stenting may be useful in drug-refractory cases with proven venous sinus stenosis and pressure gradient. Postoperative antiplatelet therapy for 6 months is required. The level of evidence is still low, and an RCT (shunt vs. stent) is ongoing in the UK.

Bariatric Surgery

When obesity is the main cause, high success rates have been reported even in cases resistant to conventional treatment. Remission has been reported with a 3–15% weight reduction. Not recommended for fulminant type.

Q Does surgery on one side affect both eyes?

Unilateral ONSF has been confirmed to improve contralateral papilledema. In a 2-year follow-up study of 9 patients with idiopathic intracranial hypertension, bilateral visual improvement was reported in all cases. The expected protective effect on the contralateral eye after unilateral surgery is one of the important features of this procedure.

Q Can symptoms recur after surgery?

Clinical recurrence has been reported in 32% of patients. If recurrence occurs, additional surgical treatment (reoperation, shunt surgery, or stent placement) may be necessary. Regular ophthalmologic examinations for follow-up are important.

6. Pathophysiology and Detailed Mechanism of Onset

Optic Nerve Damage Due to Increased Intracranial Pressure

The subarachnoid space of the optic nerve is continuous with that of the central nervous system. When elevated ICP is transmitted along the entire length of the optic nerve to the optic disc, damage occurs through the following mechanisms.

Increased intraneural pressure → impaired axonal transport → axonal swelling
Swelling impairs optic nerve perfusion → ischemia of the optic disc and optic nerve
Progression of ischemia → vision loss

The pattern of vision loss begins with enlargement of the blind spot in the early stage and progresses to peripheral visual field defects.

Mechanism of action of ONSF

The mechanism by which ONSF protects the optic nerve can be divided into two stages.

Direct pressure reduction: CSF outflow through dural incision.
Long-term maintenance effect: Prevention of CSF reaccumulation by fibrosis and scar formation at the incision site. Increased blood flow in the posterior ciliary arteries has also been reported, which is thought to contribute to improved optic disc perfusion.

Important point: ONSF does not lower ICP. It only exerts a local protective effect on the optic nerve, so no effect on systemic symptoms such as headache can be expected.

Pathophysiology of Idiopathic Intracranial Hypertension

The exact mechanism of intracranial hypertension in idiopathic intracranial hypertension is not fully understood. Dysregulation of CSF dynamics and involvement of metabolic and hormonal factors are considered. Idiopathic intracranial hypertension is increasingly recognized as a systemic metabolic disease independent of obesity, and androgen dysregulation has also been suggested.

Mechanism of ATRA-Induced Pseudotumor Cerebri¹⁾

ATRA is a vitamin A derivative that stimulates RAR receptors in the choroid plexus, increasing CSF production. Impaired CSF absorption at the arachnoid granulations is also speculated to be involved.

7. Latest Research and Future Prospects (Research Stage Reports)

Latest Findings from Meta-Analysis (2024)

Prokop et al. (2024) conducted a systematic review and meta-analysis of 19 studies and 1159 observations, comprehensively evaluating visual outcomes of ONSF³⁾. They reported a visual acuity improvement rate of 41.09% (95% CI: 29–55%), visual field improvement rate of 76.34% (95% CI: 61–87%), and papilledema improvement rate of 97% (95% CI: 84–100%). Surgical delay beyond 6 months after diagnosis significantly worsened visual field outcomes (OR 0.06, 95% CI 0.005–0.70). Clinical recurrence was observed in 32%.

Findings from Case Reports

Latif et al. (2023) performed unilateral medial transconjunctival ONSF in 9 patients (all female, mean age 24 years) with idiopathic intracranial hypertension and followed them for 2 years ²⁾. Preoperative BCVA (logMAR) was 0.5±0.28 in the better eye and 1.0±0.57 in the worse eye. Improvement at 1 week postoperatively (better eye 0.27±0.32, p=0.001) was maintained at 2 years (better eye 0.30±0.30, p=0.002). Bilateral effects from unilateral surgery were confirmed in all cases. Headache improvement and successful medication tapering were achieved in 66.67%.

Hokazono et al. (2023) treated a 32-year-old woman with ATRA (45 mg/m²)-induced pseudotumor cerebri syndrome (lumbar puncture opening pressure 42 cm H₂O) with a combination of ATRA dose reduction, acetazolamide 2 g/day, and right eye ONSF ¹⁾. Complete recovery was achieved at 6 months, with 20/20 vision in both eyes, normal visual fields, resolution of papilledema, and resolution of abducens nerve palsy.

Barh et al. (2021) performed right eye ONSF in a 13-year-old girl with intracranial hypertension (opening pressure 75 cm H₂O) associated with moyamoya disease (left ICA stenosis + left MCA occlusion) ⁴⁾. She was refractory to conservative treatment (mannitol, acetazolamide, topiramate), but at 1 month postoperatively, vision improved to 3/60 in the right eye and 6/24 in the left eye, and bilateral papilledema resolved. At 6 months, vision was maintained at 6/36 in the right eye and 6/24 in the left eye.

Endoscopic transconjunctival ONSF

This is a new approach that offers the advantages of minimal invasiveness, shorter operative time, and no need for muscle disinsertion. It is expected to reduce tissue damage, but standardization has not yet been achieved ³⁾.

Future challenges

Establishment of standardized surgical techniques
Determination of optimal surgical timing (strengthening evidence for early intervention)
Prospective comparative studies between surgical approaches
Identification of patient-specific outcome predictors
RCT of ONSF vs shunt vs stent (ongoing in the UK)
RCT of GLP-1 receptor agonist (exenatide) for IIH

8. References

Hokazono K, Cunha LP, Preti RC, Zacharias LC, Monteiro MLR. Optic nerve sheath fenestration as adjuvant treatment for severe pseudotumor cerebri syndrome induced by all-trans retinoic acid. Case Rep Ophthalmol. 2023;14:326-330.
Latif S, Rizwan A, Khan AA, Zahra S. Optic nerve sheath fenestration for salvaging acutely threatened vision in Idiopathic Intracranial Hypertension - A two-year completed follow up. Pak J Med Sci. 2023;39(6):1853-1857.
Prokop K, Opchowska A, Siekiewicz A, Lisowski L, Mariak Z, Lyso T. Effectiveness of optic nerve sheath fenestration in preserving vision in idiopathic intracranial hypertension: an updated meta-analysis and systematic review. Acta Neurochir. 2024;166:476.
Barh A, Mukherjee B, Ambika S. Optic nerve sheath fenestration for visual rehabilitation in moyamoya disease. Saudi J Ophthalmol. 2020;34:223-226.

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