Visual field defects

A visual field defect is loss of part of the visual field, found on examination or reported by the patient. It localises the lesion along the visual pathway: retina, optic nerve, chiasm, optic tract, optic radiation or occipital cortex.

Anatomy. Retinal and optic nerve lesions cause monocular, arcuate, altitudinal or central loss. Chiasmal lesions cause bitemporal loss. Lesions behind the chiasm cause homonymous loss (same side in both eyes) with congruity increasing towards the occipital cortex. Macular sparing is typical of occipital cortex lesions with dual blood supply.

Classification.

• Monocular: retinal disease (detachment, vascular occlusion, retinitis pigmentosa), glaucoma (arcuate, nasal step), optic nerve (optic neuritis, ischaemic optic neuropathy, compression).
• Bitemporal: chiasmal compression (pituitary adenoma, craniopharyngioma, meningioma, aneurysm).
• Homonymous: hemianopia, quadrantanopia (temporal lobe: upper "pie in the sky"; parietal lobe: lower), central scotoma, and macular sparing.
• Constricted (tunnel) fields: glaucoma, retinitis pigmentosa, papilloedema, functional.
• Altitudinal: ischaemic optic neuropathy, retinal artery branch occlusion.

Key distinctions. Sudden painless homonymous loss indicates a stroke. Bitemporal loss with headache and endocrine features indicates a pituitary lesion. Arcuate loss with a raised intraocular pressure indicates glaucoma. A spiral field with inconsistent results indicates functional loss.

History.

• Onset (sudden, gradual) and laterality.
• Description: blind spot, missing half, bumping into objects on one side, missing words.
• Associated symptoms: headache, nausea, double vision, weakness, speech or sensory changes, eye pain, trauma.
• Endocrine symptoms: amenorrhoea, galactorrhoea, acromegaly features, loss of libido, fatigue, thirst and polyuria.
• Vascular risk factors, atrial fibrillation, previous eye disease, family history of glaucoma, cancer, and drug history.

Drug history. Vigabatrin (concentric constriction), ethambutol, amiodarone, hydroxychloroquine, topiramate, anticoagulants, and oestrogens.

Examination.

• Visual acuity, colour vision and pupils (relative afferent defect).
• Confrontation fields: finger counting and red target, each eye separately, then both together. Test for visual inattention.
• Eye movements, intraocular pressure, and dilated fundus (disc cupping and pallor, swelling, haemorrhage, retinal disease).
• Blood pressure, pulse rhythm, carotid bruit, and a full neurological examination.
• Endocrine examination (visual field, features of acromegaly, hypopituitarism, thyroid).

Red flags

• Sudden onset homonymous defect, or with weakness, speech or sensory deficits (stroke, haemorrhage)
• Sudden severe headache with visual loss (pituitary apoplexy, subarachnoid haemorrhage)
• Bitemporal loss with headache or endocrine symptoms (pituitary tumour)
• Rapid progression, papilloedema, or neurological signs (tumour, raised intracranial pressure)
• Relative afferent pupillary defect with painless progressive loss (compressive neuropathy)
• Monocular loss within hours (artery occlusion, giant cell arteritis, detachment)
• Visual field loss with pain on eye movement (optic neuritis)
• Cancer history, anticoagulation, or atrial fibrillation
• Child with field loss or squint

Special groups. Children: optic pathway glioma, craniopharyngioma, hydrocephalus, and retinal dystrophies. Pregnancy: pituitary enlargement, pituitary apoplexy (Sheehan), idiopathic intracranial hypertension, and pre-eclampsia. Older adults: stroke, glaucoma, macular disease. Region specific: neurocysticercosis, tuberculoma and cerebral malaria.

Retinal

• Retinal detachment, retinal artery and vein occlusion, diabetic retinopathy, macular degeneration, retinitis pigmentosa, retinoschisis, chorioretinitis, retinal tumour, cancer associated retinopathy, toxic retinopathy

Optic nerve

• Glaucoma (primary open angle, normal tension, angle closure), optic neuritis, ischaemic optic neuropathy (arteritic, non-arteritic), compressive optic neuropathy (meningioma, glioma, aneurysm, thyroid eye disease), toxic and nutritional neuropathy, papilloedema, optic disc drusen, traumatic optic neuropathy, Leber hereditary optic neuropathy

Chiasm and sellar region

• Pituitary adenoma and apoplexy, craniopharyngioma, meningioma (tuberculum sellae), Rathke cleft cyst, internal carotid aneurysm, chiasmal glioma, optic neuritis, sarcoidosis, hypophysitis, empty sella, trauma, hydrocephalus

Retrochiasmal (tract, radiation, cortex)

• Ischaemic stroke (middle cerebral artery, posterior cerebral artery), intracerebral haemorrhage, subdural haematoma
• Brain tumour (primary, metastasis), abscess, tuberculoma, neurocysticercosis, toxoplasmosis, progressive multifocal leukoencephalopathy
• Multiple sclerosis, posterior reversible encephalopathy syndrome, migraine, seizures (post-ictal), posterior cortical atrophy, traumatic brain injury, hypoxic injury
• Arteriovenous malformation, cavernous malformation

Functional

• Tunnel vision and spiral fields, inconsistent results

Reasoning. Define the field defect by confrontation and formal perimetry. Image the pathway according to the pattern: brain MRI for retrochiasmal, MRI pituitary for bitemporal, and eye tests for monocular loss.

First line. Visual acuity, pupils, confrontation fields, intraocular pressure, fundoscopy and blood pressure.

Targeted tests.

• Automated static perimetry (Humphrey) or kinetic perimetry (Goldmann), repeated for reliability.
• Optical coherence tomography of the retinal nerve fibre layer and macula, fundus photography, and gonioscopy.
• Emergency CT head for sudden homonymous loss, with CT angiography.
• MRI brain with diffusion weighted imaging and angiography for stroke.
• MRI brain and orbits with gadolinium for tumour, demyelination and chiasmal lesions.
• MRI of the pituitary for bitemporal loss.
• Pituitary hormone profile: prolactin, cortisol (9 am, with short synacthen test if indicated), thyroid stimulating hormone and free thyroxine, luteinising hormone, follicle stimulating hormone, testosterone or oestradiol, insulin like growth factor 1, electrolytes, and plasma and urine osmolality when polyuria.
• ESR, C reactive protein and platelets for giant cell arteritis. Full blood count, glucose, HbA1c, lipids, syphilis serology, HIV, angiotensin converting enzyme, and aquaporin-4 and MOG antibodies by suspicion.
• Carotid duplex, echocardiography, and prolonged cardiac rhythm monitoring for embolic stroke. EEG when seizures are suspected.
• Lumbar puncture with opening pressure (over 25 cmH2O in adults is abnormal), after imaging.

Limitations. Perimetry depends on patient attention and learning. Early chiasmal compression can be missed on confrontation. MRI diffusion changes may lag in small infarcts.

Acute stroke (sudden homonymous loss).

Emergency stroke care:

• alteplase 0.9 mg/kg IV (maximum 90 mg, 10 percent as a bolus over 1 minute and the remainder over 60 minutes) within 4.5 hours when haemorrhage is excluded, or tenecteplase 0.25 mg/kg IV as a single bolus (maximum 25 mg)
• blood pressure under 185/110 mmHg before and under 180/105 mmHg for 24 hours after thrombolysis
• aspirin 300 mg orally daily when thrombolysis is not given
• thrombectomy referral for large vessel occlusion
• atorvastatin 80 mg orally at night
• secondary prevention including atrial fibrillation anticoagulation (apixaban 5 mg orally twice daily; 2.5 mg twice daily if two of age 80 or more, weight 60 kg or less, creatinine 133 micromol/L or more)

Visual rehabilitation (scanning training, prisms) and driving advice.

Intracerebral haemorrhage. Systolic blood pressure 130 to 150 mmHg and neurosurgical referral. Reverse anticoagulants:

• warfarin: vitamin K 5 to 10 mg IV with prothrombin complex concentrate 25 to 50 IU/kg adjusted to INR and product label
• dabigatran: idarucizumab 5 g IV
• apixaban or rivaroxaban: andexanet alfa or prothrombin complex concentrate dosed as the product label states

Pituitary apoplexy (emergency). Hydrocortisone 100 mg IV then 50 mg IV every 6 hours, correction of sodium and fluid balance, and urgent neurosurgical and endocrine care.

Pituitary adenoma and chiasmal compression. Endocrine and neurosurgical care:

• transsphenoidal surgery for visual loss
• prolactinoma: cabergoline 0.25 mg orally twice weekly increased by 0.25 mg every 4 weeks to a usual 0.5 to 2 mg weekly (monitor for impulse control disorders and valvular disease)
• hormone replacement: hydrocortisone 15 to 25 mg daily in divided doses, and levothyroxine 1.6 micrograms/kg daily started after cortisol replacement
• radiotherapy for residual disease

Glaucoma. Lower intraocular pressure with one of:

• latanoprost 0.005 percent 1 drop at night
• timolol 0.5 percent 1 drop twice daily (avoid in asthma, heart block, bradycardia)
• dorzolamide 2 percent 1 drop three times daily
• brimonidine 0.2 percent 1 drop twice daily

Laser or surgery by ophthalmology. For acute angle closure give acetazolamide 500 mg IV or orally, timolol 0.5 percent, apraclonidine 1 percent and pilocarpine 2 percent once pressure is falling, with same day ophthalmology.

Giant cell arteritis. Prednisolone 40 to 60 mg orally each morning started before biopsy, with aspirin 75 mg daily. With visual symptoms give methylprednisolone 500 mg to 1 g IV daily for 3 days. Same day specialist review.

Optic neuritis. Methylprednisolone 1 g IV daily for 3 to 5 days under neurology and ophthalmology care.

Retinal detachment and artery occlusion. Immediate ophthalmology; artery occlusion as an acute stroke equivalent with the stroke team.

Intracranial tumour and mass lesion. Dexamethasone 10 mg IV then 4 mg every 6 hours for vasogenic oedema (gastric protection and glucose monitoring); neurosurgical and oncology referral.

Idiopathic intracranial hypertension.

• Weight loss and acetazolamide 500 mg orally twice daily, increased by 500 mg each week to a maximum of 4 g daily as tolerated (halve when creatinine clearance is 10 to 50 mL/min).
• Serial fields, and neurosurgical or ophthalmic procedures for threatened vision.

Infective causes.

• Brain abscess: neurosurgical drainage with ceftriaxone 2 g IV every 12 hours plus metronidazole 500 mg IV every 8 hours.
• Tuberculoma: isoniazid, rifampicin, pyrazinamide and ethambutol with dexamethasone.
• Neurocysticercosis: albendazole 15 mg/kg daily in 2 doses with prednisolone 1 mg/kg.
• Toxoplasmosis: trimethoprim with sulfamethoxazole or pyrimethamine with sulfadiazine.

Drug toxicity. Stop vigabatrin, ethambutol or other culprit drugs after specialist advice.

Visual rehabilitation and safety. Low vision services, occupational therapy, orientation and mobility training, scanning exercises for hemianopia, prisms, driving restriction until the legal field limits are met, and falls prevention.

Monitoring. Repeat perimetry (glaucoma every 3 to 12 months, chiasmal lesions after treatment at 6 weeks and 3 to 6 months), pituitary hormone levels, optical coherence tomography, and neurological review.

Referral and escalation. Immediate stroke team for sudden homonymous loss. Same day neurosurgery and endocrinology for pituitary apoplexy and compressive chiasmal lesion with deterioration. Ophthalmology for glaucoma, retinal disease and optic nerve disease. Neurology for demyelination and other central causes. Oncology for tumours.

Admission criteria. Stroke, haemorrhage, pituitary apoplexy, rapidly progressive loss, raised intracranial pressure, or giant cell arteritis with visual loss.

Discharge and safety netting. Return for sudden loss, new headache, double vision, weakness, speech or sensory change, eye pain, or progression of field loss. Advise on driving restriction and safety.