Compressive Optic Neuropathy

Optic nerve dysfunction caused by external pressure on the nerve in the orbit, optic canal, or intracranial space, leading to axonal conduction block and then axonal loss. Early recognition allows recovery because dysfunction is initially reversible.

• Causes by site:
  • Orbital: thyroid eye disease (enlarged extraocular muscles at the apex), optic nerve sheath meningioma, optic nerve glioma, orbital tumours (cavernous haemangioma, lymphoma, metastases), idiopathic orbital inflammation, abscess, and haematoma.
  • Optic canal and sphenoid region: sphenoid wing meningioma, fibrous dysplasia, hyperostosis, mucocele, and trauma.
  • Intracranial prechiasmal: pituitary adenoma extending upwards, tuberculum sellae and planum meningioma, craniopharyngioma, anterior communicating and ophthalmic artery aneurysm, dolichoectatic carotid arteries, and arachnoid cyst.
  • Infiltrative: sarcoid, lymphoma, leukaemia, and carcinomatous meningitis.
• Pituitary tumours are the commonest cause of chiasmal and optic nerve compression in adults; thyroid eye disease is the commonest cause of orbital compressive neuropathy.

• Slowly progressive, painless unilateral (or asymmetric) visual loss over weeks to years; acute presentation with haemorrhage (apoplexy, aneurysm) or thyroid disease.
• Dyschromatopsia (early), relative afferent pupillary defect, central, arcuate or junctional scotoma; temporal field loss in the fellow eye (junctional scotoma).
• Disc: normal early, then swelling or pallor (atrophy); optociliary shunt vessels (meningioma); choroidal folds.
• Associated signs: proptosis, restricted eye movements (orbital), headache, hypopituitarism (pituitary disease), hyperprolactinaemia features, and cranial neuropathies.
• Thyroid eye disease: lid retraction, chemosis, restricted motility, and apical crowding, even with minimal proptosis.

• Visual acuity, colour vision, pupils, automated perimetry (central fields, with temporal fields of the fellow eye), dilated fundus examination, and optical coherence tomography of the retinal nerve fibre layer and ganglion cell layer (thinning predicts poor recovery).
• Neuroimaging: MRI brain and orbits with gadolinium and fat suppression (the investigation of choice); CT orbits for bone and calcification; CT or MR angiography for aneurysm.
• Endocrine tests: prolactin, IGF-1, cortisol, thyroid function, LH, FSH, testosterone or oestradiol; thyroid antibodies.
• Blood tests: ESR, CRP, ACE, ANCA, IgG4; biopsy if inflammatory or neoplastic cause is unclear.

• Decompress the nerve and treat the cause:
  • Thyroid eye disease: intravenous methylprednisolone 500 mg to 1 g daily for 3 days (or alternate days), then oral prednisolone; urgent orbital decompression if no improvement within 1 to 2 weeks or if vision is rapidly falling; adjuncts: radiotherapy, teprotumumab 10 mg/kg then 20 mg/kg every 3 weeks.
  • Pituitary adenoma: transsphenoidal surgery (endoscopic) for visual compromise; prolactinoma: cabergoline 0.25 mg twice weekly increased every 4 weeks to a maximum of 1 to 3 mg weekly (shrinkage within days to weeks); apoplexy: hydrocortisone 100 mg IV then 50 mg every 6 hours and urgent surgery.
  • Meningioma: surgery when accessible and resectable, or fractionated radiotherapy (50.4 to 54 Gy in 28 to 30 fractions) for optic nerve sheath meningioma; observation for small asymptomatic tumours.
  • Aneurysm: endovascular coiling or clipping.
  • Fibrous dysplasia: optic canal decompression only for documented progressive visual loss.
  • Lymphoma and sarcoid: chemotherapy or radiotherapy for lymphoma; prednisolone 1 mg/kg and steroid-sparing agents for sarcoid.
  • Abscess and haematoma: drainage and antibiotics.
• Monitor acuity, fields, colour vision, and imaging every 1 to 3 months after treatment.
• Predictors of recovery: short duration of symptoms, normal disc, preserved ganglion cell layer, and early decompression; pallor and ganglion cell loss predict limited recovery.
• Low-vision rehabilitation for residual deficits.