Optic Chiasm Inflammation

Key Points at a Glance

Highlights of this disease

• Chiasmitis is a type of optic neuritis involving inflammation of the optic chiasm.
• Bitemporal hemianopsia is the typical visual field defect pattern, and the type of visual field loss varies depending on the lesion location in the optic chiasm.
• It often occurs as optic neuritis associated with multiple sclerosis (MS).
• Causes include idiopathic, infectious, toxic, autoimmune, and antibody-mediated etiologies.
• Unlike optic neuritis, idiopathic chiasmitis often does not involve eye pain.
• Steroid pulse therapy is the first-line treatment, with reports of 97% of affected eyes recovering to visual acuity of 20/40 or better.
• Approximately 40% of idiopathic chiasmitis progresses to MS within 3 years, requiring long-term follow-up.

1. What is chiasmitis?

Chiasmitis, also called chiasmal optic neuritis, is a type of optic neuritis involving inflammation of the optic chiasm. It is characterized by acute vision loss, visual field defects mainly as bitemporal hemianopia, and imaging findings of the chiasm.

It often occurs with optic neuritis associated with multiple sclerosis (MS). In 1975, Bell first documented the pathological correlation between MS and chiasmal lesions, and in 1987, Rosenblatt reported chiasmal optic neuritis on MRI. ²⁾

Idiopathic chiasmitis and demyelinating optic neuritis are considered different manifestations of the same pathological process. Risk factors for idiopathic chiasmitis are similar to those for optic neuritis, with a higher prevalence in women and young adults.

Kawasaki & Purvin conducted the largest study following 20 cases of idiopathic chiasmitis and reported that the course of patients was similar to optic neuritis. Within 3 years, 6 cases (40%) were diagnosed with clinically definite MS, and 4 of them had a second demyelinating event within 1 year.

Q What is the difference between optic chiasmitis and optic neuritis?

A

Optic chiasmitis is a type of optic neuritis, differing in that the inflammation is located in the optic chiasm. While optic neuritis typically presents with a central scotoma in one eye, optic chiasmitis shows visual field defects characteristic of chiasmal lesions, such as bitemporal hemianopia. The pathophysiology and treatment are similar, and they are considered different manifestations of the same demyelinating process.

2. Main symptoms and clinical findings

Subjective symptoms

• Blurred vision and decreased visual acuity: Often acute onset. Worsens over days to weeks, then stabilizes and improves.
• Photopsia: Usually transient, perceived as flashes or glare.
• Temporal visual field darkening: The temporal side of the visual field appears dark.
• Hemifield slide phenomenon and diplopia: The patient perceives image misalignment despite normal eye movements.
• Loss of depth perception at the fixation point: Due to impaired binocular vision associated with bitemporal hemianopia.
• Eye pain: Usually absent in idiopathic cases. In the report by Kawasaki & Purvin, only 20% of 20 cases had eye pain.

Q Is there pain in chiasmitis?

A

Idiopathic chiasmitis usually does not involve eye pain. In a report of 20 cases, only 20% had eye pain. This is an important difference from typical optic neuritis, where eye movement pain is present in about 60% of cases. However, infectious or autoimmune causes may be accompanied by headache.

Clinical Findings

The pattern of visual field defects varies depending on the location of the lesion within the optic chiasm.

Anterior Chiasm

Junctional scotoma: Central scotoma in one eye with superotemporal visual field defect in the contralateral eye.

Traquair junctional scotoma: Temporal visual field defect only in the ipsilateral eye.

Body of the Chiasm

Bitemporal hemianopia: The most typical finding of chiasmal lesions.

Respect for the vertical meridian: The temporal visual fields of both eyes are symmetrically lost.

Posterior chiasm

Bitemporal hemianopic scotoma: Due to damage to posterior crossing fibers.

Lateral lesions: Damage to non-crossing fibers results in homonymous hemianopia.

Other clinical findings include the following.

• Decreased central vision: Ranges from mild to severe depending on the extent and severity of the lesion.
• Abnormal pupillary light reflex: The pupillary light response may become sluggish.
• Band atrophy: In the chronic phase, the nasal and temporal sides of the optic disc atrophy, while the superior and inferior sides are preserved, showing a “bow-tie” pattern.

3. Causes and Risk Factors

The causes of optic chiasm inflammation are diverse.

Category	Causative disease
Infectious	Tuberculosis, syphilis, EBV, varicella-zoster virus, mumps, Lyme disease, cryptococcus, cysticercosis, schistosomiasis
Inflammatory	Sarcoidosis
Autoimmune	MS, SLE
Antibody-mediated	NMO (AQP4 antibody), MOGAD (MOG antibody)
Vasculitic	Giant cell arteritis
Ischemic	Moyamoya disease
Toxic	Ethambutol

Syphilis can cause chiasmal inflammation in association with uveitis. Ishibe et al. reported a case of syphilitic uveitis complicated by chiasmal optic neuritis presenting with bitemporal hemianopic visual field defects. ⁴⁾

In toxic optic neuropathy due to ethambutol, damage may extend to the optic chiasm, resulting in bitemporal hemianopia. ³⁾

In AQP4 antibody-positive NMOSD, isolated chiasmal lesions are characteristic, and MOGAD-related optic neuritis may also extend to the chiasm. ⁵⁾

Risk factors

• Female
• Young age (15–45 years)

Prevention and daily care

Since optic chiasmitis may progress to multiple sclerosis, long-term follow-up in collaboration with a neurologist is necessary after onset. If you experience sudden vision loss or visual field abnormalities, consult an ophthalmologist early.

Q What is the risk of developing multiple sclerosis from optic chiasmitis?

A

In a study tracking 20 cases of idiopathic optic chiasmitis, 40% were diagnosed with clinically definite MS within 3 years. Among them, 4 cases had a second demyelinating event within 1 year, highlighting the importance of early follow-up. This risk is considered similar to the rate of MS conversion from optic neuritis.

4. Diagnosis and Examination Methods

There are no definitive diagnostic criteria for optic chiasmitis. Diagnosis is made clinically based on the presence of visual field defects consistent with the pattern of chiasmal lesions.

MRI

MRI is the most important imaging test.

• Imaging technique: Fat-suppressed sequences (STIR) show enlargement and high signal intensity of the optic chiasm. Contrast-enhanced T1-weighted images confirm enhancement.
• Imaging planes: In addition to axial sections, coronal and sagittal sections are useful.
• Findings: Enlargement and contrast enhancement of the optic chiasm are observed. In the report by Kawasaki & Purvin, enlargement or contrast enhancement of the optic chiasm was found in 12 of 15 patients (80%) who underwent MRI.
• FLAIR images: Evaluate the presence of demyelinating lesions near the lateral ventricles to assess the risk of MS.

Even if MRI findings are normal, optic chiasmitis cannot be ruled out. Cases of SLE-related optic chiasmitis with normal MRI have been reported. ¹⁾

Blood tests and cerebrospinal fluid tests

The following are evaluated to identify the cause.

• Anti-AQP4 antibody: Essential for evaluating NMOSD. Early evaluation is important in cases unresponsive to steroids or with a relapsing course.
• Anti-MOG antibody: Used to differentiate MOGAD-related optic neuritis.
• Cerebrospinal fluid (CSF) analysis: Evaluate MS based on the presence of oligoclonal bands. In infectious cases, consider CSF RPR and Treponema pallidum antibodies. ⁴⁾
• Syphilis serology: RPR, TPHA (Treponema pallidum hemagglutination assay).

Features of Atypical Optic Neuritis

If the following features are present, suspect atypical optic neuritis and investigate the underlying disease.

• Age outside 15–45 years
• Bilateral onset
• Progression of symptoms beyond 2 weeks after onset
• Steroid-dependent course
• Presence of systemic symptoms

Optical Coherence Tomography (OCT) and Optical Coherence Tomography Angiography (OCTA)

• OCT: Evaluates thinning of the peripapillary retinal nerve fiber layer (RNFL) and macular ganglion cell-inner plexiform layer (mGCIPL) over time. In the chronic phase, it shows a pattern corresponding to band atrophy.
• OCTA: Cuna et al. reported that in MS-related optic chiasmitis, the superficial capillary plexus density diffusely decreases. In compressive optic chiasmopathy, a selective decrease corresponding to the crossing fibers is observed, whereas in demyelinating disease, a global decrease is seen. ²⁾

5. Standard Treatment

There is no established treatment for optic chiasmitis, and treatment is based on the underlying cause.

Pharmacotherapy

Steroid pulse therapy is the first-line treatment.

• Administration: Intravenous methylprednisolone 1,000 mg/day for 3 days.
• Post-therapy: In Japan, oral prednisolone after pulse therapy (post-therapy) is not performed. In the Optic Neuritis Treatment Trial (ONTT) overseas, a regimen of oral prednisolone 1 mg/kg/day for 11 days after pulse therapy is used.
• Side effects: Be cautious of hyperglycemia, peptic ulcers, and induction of infections.

AQP4 antibody-positive cases

If steroid pulse therapy is ineffective, plasma exchange may be performed.

Treatment by cause

• Infectious: Use antibacterial or antiviral drugs according to the causative microorganism. For syphilitic cases, systemic administration of penicillin antibiotics is the standard, and there are reports of improvement with oral amoxicillin. ⁴⁾
• Toxic (ethambutol): Immediately discontinue the causative drug. Visual recovery may take several months. ³⁾
• Autoimmune (SLE): In addition to steroids, immunosuppressants such as cyclophosphamide or mycophenolate mofetil may be used. ¹⁾

Prognosis

In a follow-up of 20 cases by Kawasaki & Purvin, 97% of affected eyes improved to visual acuity of 20/40 (0.5) or better, and all visual fields stabilized or improved. Only one case showed progressive visual loss beyond one month.

Precautions and side effects in treatment

Treatment with oral steroids alone has been reported to increase the recurrence rate of optic neuritis and is not recommended. If steroid pulse therapy is ineffective or shows a steroid-dependent course, consider the possibility of atypical optic neuritis such as NMOSD or MOGAD, and perform anti-AQP4 antibody and anti-MOG antibody tests early.

Q What should I do if steroid pulse therapy is not effective?

A

In cases where steroids are ineffective, consider the possibility of anti-AQP4 antibody-positive NMOSD and perform plasma exchange. If the course is steroid-dependent, investigate the underlying disease such as MOGAD or SLE and consider combination immunosuppressive therapy. For details, see the section on “Causes and Risk Factors” (#3-causes-and-risk-factors).

6. Pathophysiology and Detailed Mechanism of Onset

The pathophysiology of optic chiasmitis is not fully understood. The mechanism varies depending on the cause.

Demyelinating (idiopathic, MS-related)

Idiopathic optic chiasmitis, where the cause is not identified in the early stage, is thought to result from demyelination. An autoimmune reaction against the myelin sheath damages nerve fibers in the optic chiasm. Some cases are later diagnosed as MS, and it may belong to the same demyelinating spectrum as optic neuritis.

Infectious/Inflammatory

Infectious or inflammatory causes can directly damage the optic chiasm through ischemia or degenerative changes. It may also occur as an immune-mediated parainfectious or post-infectious sequela.

Toxic (Ethambutol)

Ethambutol impairs autophagy in retinal ganglion cells, inducing apoptosis. It also disrupts oxidative phosphorylation via metal chelation, leading to mitochondrial dysfunction. ³⁾ It is hypothesized that optic neuropathy progresses proximally to involve the optic chiasm.

Antibody-Mediated

AQP4 antibodies target aquaporin-4 channels on astrocytes, forming lesions that preferentially affect the posterior optic nerve, including the optic chiasm. ⁵⁾ MOG antibodies target myelin oligodendrocyte glycoprotein, primarily damaging the anterior optic nerve but can extend to the chiasm. ⁵⁾

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

For Patients: Please Read Carefully

The following content is currently at the research stage or in clinical trials and is not standard treatment available at general hospitals. It is reference information for professionals regarding future medical developments.

Evaluation of Demyelinating Optic Chiasmitis Using OCTA

Cuna et al. (2022) performed longitudinal evaluation using OCTA over 3 years in MS-related optic chiasmitis. Despite visual acuity recovering to 20/20, progressive decreases in superficial capillary plexus density and ganglion cell complex were observed. While compressive optic chiasm disorders show selective vascular density reduction corresponding to crossing fibers, demyelinating optic chiasmitis exhibited diffuse reduction. This difference is speculated to be because demyelinating lesions cause more extensive optic nerve damage. ²⁾

Evaluation of Toxic Chiasmal Disorders Using mGCIPL

Lin et al. (2022) reported that nasal thinning of the macular ganglion cell–inner plexiform layer (mGCIPL) reflects retrograde trans-synaptic degeneration in ethambutol-related chiasmal disorders. Even after best-corrected visual acuity recovered to 20/20, mGCIPL thinning persisted, suggesting it may serve as a structural marker of irreversible neuronal damage. ³⁾

Combined Syphilitic Uveitis and Chiasmal Optic Neuritis

Ishibe et al. (2026) reported a case of syphilitic uveitis (acute syphilitic posterior placoid chorioretinitis) complicated by chiasmal optic neuritis. The bitemporal hemianopia-like visual field defect could not be explained by fundus findings alone, and MRI revealed contrast enhancement of the optic chiasm. This case highlights the importance of neuroimaging to rule out intracranial lesions when visual field defects do not match fundus findings in ocular syphilis. ⁴⁾

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8. References

1. Almeida GB, Moro N, Monteiro MLR. Recurrent and Reversible, Bitemporal Field Defect from Presumed Chiasmitis in a Patient with Systemic Lupus Erythematosus. Neuro-Ophthalmology. 2021;45(2):117-119.
2. Cuna A, Pellegrini F, Interlandi E, et al. Optical Coherence Tomography Angiography in Chiasmitis. Case Rep Ophthalmol. 2022;13:517-522.
3. Lin YW, Wang JK, Huang TL. Ethambutol optic neuropathy with correspondent chiasmitis manifestation in magnetic resonance imaging. Taiwan J Ophthalmol. 2022;12:343-346.
4. Ishibe T, Otsuka M, Itotani M, et al. Syphilitic Uveitis-Associated Chiasmal Optic Neuritis Presenting As Bitemporal Hemianopia-Like Visual Field Defects. Cureus. 2026;18(1):e100656.
5. Cacciaguerra L, Flanagan EP. Diagnosis and Treatment of NMOSD and MOGAD. Neurol Clin. 2024;42(1):81-114.