Sudden Painless Visual Loss

Introduction

Sudden painless visual loss is a presentation rather than a diagnosis, and the reason it is taught as a topic in its own right is that the differential contains several conditions in which the treatment window is measured in hours. Getting to the right diagnosis quickly matters more than knowing any individual condition in great depth.

The absence of pain is itself useful information, because it excludes most of the anterior segment - acute angle closure, keratitis, uveitis and scleritis are all painful. What remains is a shorter list concerning the retina, the optic nerve, the vascular supply to either, and the visual pathway behind the eye.

The structure that follows is a way of navigating that list rapidly at the bedside. It uses four questions, in order, and it is worth practising because it converts a long and intimidating differential into a series of binary choices. The individual conditions have their own articles; this one is about how to get to them.

The four questions

1. Is the loss transient or persistent? Transient loss with full recovery points to amaurosis fugax, giant cell arteritis, papilloedema, migraine or a posterior circulation TIA. Persistent loss points to a structural or vascular event that has already happened.
2. Is it monocular or binocular? Ask the patient to cover each eye in turn, and do not accept their initial answer - many people with a homonymous hemianopia are convinced the problem is in one eye. Monocular means eye or optic nerve; binocular means chiasm or behind it, or a bilateral ocular process.
3. Is there a relative afferent pupillary defect? An RAPD localises the problem to the retina or optic nerve, and its absence in dense monocular loss points instead to media opacity or a cortical cause.
4. Can you see the fundus, and is it normal? An abnormal fundus usually gives the diagnosis directly. An absent view suggests media opacity - vitreous haemorrhage, dense cataract or corneal disease. A normal fundus in a patient with severe loss points to retrobulbar optic neuropathy, an occipital lesion, or a very early retinal event.

Transient visual loss

Persistent monocular loss

This is the largest group and the one where the fundus does most of the diagnostic work.

Persistent binocular loss

• Occipital (posterior cerebral artery) stroke - a congruous homonymous hemianopia, often with macular sparing, normal pupils and normal fundi. Bilateral occipital infarction produces cortical blindness, and if the patient denies being blind and confabulates, that is Anton syndrome.
• Bilateral occipital lesions from cardiac arrest, hypotension, or posterior reversible encephalopathy syndrome (PRES) in severe hypertension, eclampsia or with certain drugs
• Chiasmal compression - usually a slowly progressive bitemporal hemianopia rather than sudden loss, but pituitary apoplexy causes abrupt loss with headache, ophthalmoplegia and hypopituitarism, and is an emergency requiring hydrocortisone and neurosurgical referral
• Giant cell arteritis affecting both eyes, which may be sequential over days
• Methanol poisoning - bilateral loss with a high anion gap metabolic acidosis and dilated unreactive pupils
• Bilateral ocular disease - simultaneous bilateral retinal or optic nerve pathology is unusual and should prompt consideration of a systemic cause: severe hypertension, hyperviscosity, vasculitis or an embolic shower
• Functional visual loss - a diagnosis of exclusion, supported by tubular or spiralling fields, normal pupils and normal electrophysiology, but requiring full assessment first

Assessment

History

• Exact onset and tempo - seconds suggests arterial occlusion, hours to days suggests venous occlusion or optic neuritis, days to weeks suggests wet AMD
• Duration and recovery - and if transient, exactly how long and how it recovered
• Pattern of loss - a curtain, a central patch, one side of the field, or total. Ask the patient to draw it.
• Preceding symptoms - flashes and floaters (detachment), distortion (macular disease), transient obscurations (papilloedema or GCA), amaurosis fugax
• Pain - including specifically pain on eye movement, since optic neuritis is often reported as painless until asked directly
• Systemic symptoms in the over-50s - headache, jaw claudication, scalp tenderness, shoulder and hip girdle stiffness, weight loss and fever
• Vascular risk factors - hypertension, diabetes, smoking, hyperlipidaemia, atrial fibrillation, previous stroke or TIA
• Ocular history - myopia, previous cataract surgery, previous detachment, diabetic retinopathy, known AMD, and previous episodes in the other eye
• Drug history - anticoagulants, ethambutol, amiodarone, and any recent intravitreal injection or ocular surgery

Examination

1. Visual acuity in each eye separately, with glasses and with a pinhole. Improvement with a pinhole indicates a refractive or media problem.
2. Colour vision with Ishihara plates - disproportionately reduced in optic nerve disease
3. Pupils, including a careful swinging light test for an RAPD
4. Confrontation visual fields, testing across the vertical and horizontal midlines and checking for visual inattention
5. Eye movements and assessment for pain on movement, proptosis and diplopia
6. Anterior segment with fluorescein, to exclude corneal and anterior chamber pathology
7. Red reflex - absent or dulled in vitreous haemorrhage and dense cataract
8. Dilated fundoscopy - the essential examination. Assess the disc, macula, vessels and peripheral retina.
9. Palpate the temporal arteries in anyone over 50, and check the blood pressure and pulse rhythm
10. Focused neurological examination if a retrochiasmal cause is possible

Investigations

• ESR, CRP, FBC and platelets - in every patient over 50, to screen for giant cell arteritis. A raised platelet count is a useful additional pointer.
• Blood pressure, glucose or HbA1c, lipid profile and U&Es - vascular risk assessment in essentially every case
• ECG and, where embolism is suspected, prolonged rhythm monitoring and echocardiography
• Carotid imaging - Doppler or CT angiography, urgently for amaurosis fugax and CRAO
• Optical coherence tomography - the workhorse investigation, showing macular oedema, subretinal fluid, inner retinal infarction, and retinal nerve fibre layer change
• B-scan ultrasonography - where the fundus cannot be seen, to exclude retinal detachment behind a vitreous haemorrhage
• Fluorescein angiography - for choroidal neovascularisation and for capillary non-perfusion in vein occlusion
• Urgent CT head, or diffusion-weighted MRI - for suspected stroke, following the local stroke pathway; MRI brain and orbits with contrast for suspected optic neuritis or compressive lesions
• MRI pituitary for suspected chiasmal compression, and MR venography where cerebral venous sinus thrombosis is possible
• Temporal artery ultrasound and biopsy in suspected giant cell arteritis - arranged without delaying steroid treatment
• Visual fields - formal perimetry, to localise and document

Immediate management priorities

The specific treatments belong to the individual conditions, but the priorities in the first hour are consistent, and they are what an exam or a shift will test.

1. Exclude giant cell arteritis in anyone over 50. If suspected, give oral prednisolone 60 mg or IV methylprednisolone immediately, before the ESR result and before the biopsy. This is the only intervention in the whole differential that reliably prevents blindness in the fellow eye.²
2. Decide whether this is a stroke presentation. Amaurosis fugax, central retinal artery occlusion and a sudden homonymous field defect all belong on a stroke or TIA pathway with same-day assessment, imaging and secondary prevention.¹
3. Identify a macula-on retinal detachment, which needs surgery within 24 hours. Ask about flashes, floaters and a curtain in every case, and check the acuity - preserved central acuity with a peripheral field defect is the picture.
4. Identify wet AMD, which needs a macular service within 14 days. New distortion or a new central scotoma in an older patient, particularly one with known drusen or dry AMD, is the trigger.³
5. Do not be falsely reassured by a normal-looking eye. Retrobulbar optic neuritis, occipital stroke and early CRAO all present with a fundus that can look normal to an inexperienced examiner.
6. Document acuity, pupils and fundus findings in every case, including the negatives. An undocumented acuity is the commonest medicolegal weakness in these presentations.
7. Address driving and safety - patients with new visual loss should not drive until assessed, and DVLA notification may be required⁴

Putting it together

A worked pattern for a common exam vignette makes the structure concrete. A 72-year-old woman describes losing all vision in her right eye over a few seconds this morning. It was painless. She has had a headache for three weeks and her scalp is sore when she brushes her hair. Her jaw aches when she eats.

Working through the questions: the loss is persistent and monocular, so the lesion is in the right eye or its optic nerve. Examination shows an acuity of counting fingers and a right RAPD, confirming retinal or optic nerve disease rather than a media opacity. The fundus shows a pale, swollen disc, which points to anterior ischaemic optic neuropathy rather than an arterial occlusion. The systemic history of headache, scalp tenderness and jaw claudication makes this arteritic AION from giant cell arteritis.

The correct action is to give high-dose corticosteroid immediately, then send ESR, CRP and platelets, arrange temporal artery ultrasound and biopsy, and refer urgently to rheumatology and ophthalmology. Waiting for the blood results before starting steroid is the error that costs the other eye, and it is the point the question is testing.

The same four questions handle every other vignette in this differential. They do not require any information the history and a bedside examination cannot supply, they take a few minutes, and they reliably separate the conditions that need something to happen today from those that can wait for a clinic appointment. That separation is, in practice, the entire clinical skill.