Acute Onset Painless Vision Loss

Classification by Onset and Duration

1. Amaurosis Fugax (Transient Visual Loss)

• Embolic (most common) - carotid or cardiac origin
• Hemodynamic - severe carotid stenosis with hypoperfusion
• Ocular - raised IOP, hyperviscosity
• Neurologic - optic nerve lesion
• Idiopathic

• Kanski's Clinical Ophthalmology 10th Ed.

2. Central Retinal Artery Occlusion (CRAO)

Symptoms

• Sudden, profound, painless monocular vision loss occurring over seconds
• Vision usually counting fingers to light perception (94% of eyes)
• Often preceded by episodes of amaurosis fugax

Signs

• Profound RAPD (relative afferent pupillary defect) - sometimes a complete "amaurotic" pupil
• Cherry-red spot at the macula - the foveola's thin retina allows the normal choroidal circulation to show through, contrasting with surrounding pale ischaemic retina
• Pale, oedematous retina in all quadrants
• Attenuated arteries with "cattle-trucking" or "box-car" segmentation of blood column
• Peripapillary retinal swelling

CRAO - cherry-red spot at the macula with surrounding retinal pallor (Kanski's Clinical Ophthalmology 10th Ed.)

CRAO with cherry-red spot, retinal pallor, and embolic plaques visible in retinal vessels (Tintinalli's Emergency Medicine)

Special variant

• Cilioretinal artery (present in ~20% of people): if it supplies the papillomacular bundle, central vision can be partially preserved despite total CRAO
• GCA-related CRAO: absence of light perception; combined with anterior ischaemic optic neuropathy; very poor prognosis

Causes

Treatment (Time-critical - window ~4-6 hours)

1. Ocular massage - using a three-mirror contact lens or through closed eyelids. 10-15 seconds pressure, then release, for 3-5 minutes. Aims to mechanically dislodge embolus/thrombus by alternating flow.
2. Anterior chamber paracentesis - 27-gauge needle to lower IOP abruptly
3. IOP-lowering drugs - topical timolol, acetazolamide
4. CO2 inhalation / paper bag breathing - to cause vasodilation
5. IV tPA (alteplase) - 0.9 mg/kg within 4.5 hours of onset. 10% given over 1 minute, remainder over 59 minutes. Local intra-arterial thrombolysis has NOT shown benefit over conservative management. Evidence remains limited and ophthalmologists have not reached consensus.

Systemic workup (urgent - risk of stroke)

• 30% will have severe carotid disease, coincidental stroke or extreme hypertension
• 20% will have simultaneous MI or critical heart disease
• ~95% need a change in systemic medication
• 25% require urgent surgical intervention

• Kanski's Clinical Ophthalmology 10th Ed.; Tintinalli's Emergency Medicine

3. Branch Retinal Artery Occlusion (BRAO)

• Sudden, profound painless altitudinal or sectoral visual field loss
• Can go unnoticed if central vision is spared
• RAPD often present
• Fundus: cloudy white oedematous ("ground glass") retina in the ischaemic zone; "cattle-trucking" of blood column; emboli visible at bifurcation points
• FA: delayed arterial filling and hypofluorescence due to retinal swelling
• Management same as CRAO (urgent systemic evaluation, antiplatelet therapy, stroke risk reduction)
• Review at 3 months

4. Central Retinal Vein Occlusion (CRVO)

• Vision loss is variable - from vague blurring to rapid, painless, monocular loss
• Risk factors: diabetes, hypertension, dyslipidaemia, hypercoagulable states, glaucoma, vasculitis
• Classic fundus: "blood and thunder" appearance - optic disc oedema with diffuse retinal haemorrhages in all quadrants
• Distinguishing features: contralateral optic nerve is normal (unlike papilloedema); haemorrhages are peripheral (unlike optic neuritis)
• Treatment: anti-VEGF injections; laser-induced chorioretinal anastomosis
• Consult neurology and ophthalmology

5. Non-Arteritic Anterior Ischaemic Optic Neuropathy (NAION)

Symptoms

• Sudden painless monocular visual loss, frequently discovered on awakening (suggesting nocturnal hypotension plays a role)

Signs

• VA: normal or slightly reduced in ~30%; moderate-to-severe impairment in the remainder
• Visual field: typically inferior altitudinal defect (most characteristic), but also central, paracentral, quadrantic, or arcuate defects
• Dyschromatopsia proportional to visual impairment (unlike optic neuritis where colour vision is disproportionately affected)
• Diffuse or sectoral hyperaemic disc swelling with peripapillary splinter haemorrhages
• Disc swelling resolves and pallor ensues over 3-6 weeks

Prognosis

• Improvement in vision is common; recurrence in ~6%
• About 50% achieve 6/9 or better; 25% only reach 6/60 or worse
• Fellow eye involvement: ~10% after 2 years, ~15% after 5 years

Treatment

• No definitive treatment
• Exclude GCA (ESR, CRP, temporal artery biopsy if any doubt)
• Treat underlying systemic conditions
• Aspirin frequently prescribed for systemic vascular risk reduction
• Optic nerve fenestration is NOT beneficial
• Short-term steroids advocated by some authorities

6. Arteritic Anterior Ischaemic Optic Neuropathy (AAION) - GCA

Symptoms of GCA

• Scalp tenderness (noticed on combing hair)
• Headache (frontal, occipital, or temporal)
• Jaw claudication (pathognomonic) - cramp on chewing due to masseter ischaemia
• Weight loss, fever, night sweats, malaise
• Polymyalgia rheumatica (PMR) in ~50% at diagnosis
• Double vision

Ocular symptoms

• Sudden, profound unilateral visual loss, not uncommonly preceded by amaurosis fugax
• Prognosis is very poor; typically more severe than NAION

Epidemiology

• Average age: 70 years; extremely rare under 50
• Women affected 4x more than men

Investigations

1. Age ≥50 at onset
2. New headache
3. Temporal artery tenderness or decreased pulsation
4. ESR ≥50 mm/h
5. Abnormal artery biopsy (granulomatous inflammation with multinucleated giant cells)

Treatment

• Without visual symptoms: Oral prednisolone 1 mg/kg/day
• With visual symptoms / AAION: High-dose IV methylprednisolone (500 mg-1 g/day for 3 days), then oral prednisolone to prevent fellow-eye involvement
• Duration: 1-2 years; some need indefinite maintenance
• Monitor ESR and CRP
• Do not taper rapidly, especially below 10 mg/day

7. Vitreous Haemorrhage

• Mild: sudden floaters and diffuse blurring without significant VA reduction
• Dense: severe, sudden painless vision loss
• Causes: Acute posterior vitreous detachment with retinal tear or vessel avulsion, proliferative diabetic retinopathy, retinal vein occlusion, sickle cell disease, trauma, Terson syndrome (vitreous + subarachnoid haemorrhage from aneurysmal rupture)
• Investigations: B-scan ultrasound is critical to exclude retinal detachment or choroidal melanoma underlying a dense haemorrhage
• Treatment: Early vitrectomy increasingly adopted for dense haemorrhage; otherwise observation

8. Retinal Detachment

• Preceding symptoms: photopsia (flashes of light), floaters, and a "curtain or shadow" across the visual field
• If the macula is detached - sudden onset of painless, blurred central vision
• Three types:
  • Rhegmatogenous (most common) - retinal break/tear with vitreous fluid entry
  • Tractional - fibrovascular membranes pulling retina (diabetic retinopathy)
  • Exudative/serous - fluid accumulation without break (choroidal tumour, inflammation)
• Emergency if macula-on (central vision intact); surgery within 24 hours
• Examination: raised, corrugated retinal folds; if detachment is large, the retina billows forward

9. Ocular Ischaemic Syndrome (OIS)

• Results from chronic ocular hypoperfusion due to severe (>90%) ipsilateral carotid atherosclerotic stenosis
• Typically affects older patients with diabetes and hypertension
• Presents with dull periorbital ache (can be painless) and gradual or acute visual symptoms
• Signs include dilated tortuous retinal veins, retinal haemorrhages, neovascularization
• Associated with very high cardiovascular mortality

Differential Diagnosis Summary by Laterality

Immediate Emergency Assessment

1. Visual acuity both eyes
2. Pupillary responses - look for RAPD (afferent defect = retinal/optic nerve pathology)
3. Confrontation visual fields
4. Slit-lamp - anterior segment for cells/flare
5. Fundoscopy (direct and indirect) - disc, macula, vessels, vitreous, periphery
6. IOP measurement
7. B-scan ultrasound if fundus not visible

Urgent systemic workup

• BP, ECG (AF?), fasting lipids, glucose, FBC, ESR/CRP, coagulation screen
• Carotid Doppler ultrasound
• Echocardiogram if cardiac embolism suspected
• If GCA suspected: temporal artery biopsy / ultrasound; do not delay steroids

Key Mnemonics

• C - CRAO/CRVO
• R - Retinal detachment
• A - AION (NAION/AAION-GCA)
• V - Vitreous haemorrhage
• E - Embolic (amaurosis fugax)
• T - Temporal arteritis (GCA)
• V - Vascular occlusion (ophthalmic artery)