🩺 Sudden Visual Loss

Sudden visual loss is a medical emergency defined as a rapid reduction in vision occurring over seconds to days. It can be unilateral or bilateral and may be associated with pain or be entirely painless. The primary goal of assessment is to differentiate between sight-threatening conditions requiring immediate intervention (e.g., Giant Cell Arteritis or retinal detachment) and more chronic progressive losses. In the UK, most cases require an urgent ophthalmology review via an Eye Casualty or an Emergency Department.

Establish the speed of onset, duration, and whether the loss is total or partial (e.g., a field defect). Ask about associated pain; sudden painless loss suggests vascular events like CRAO, CRVO, or retinal detachment, whereas painful loss suggests optic neuritis or acute glaucoma. Screen for systemic symptoms such as headache, jaw claudication, and scalp tenderness (GCA) or flashes and floaters (retinal detachment). Identify cardiovascular risk factors, including hypertension, diabetes, and atrial fibrillation.

Assess visual acuity using a Snellen chart with the patient's own glasses or a pinhole. Perform a pupillary reflex test to look for an afferent pupillary defect (RAPD), which is characteristic of significant retinal or optic nerve pathology. Slit-lamp biomicroscopy and dilated fundoscopy are essential to visualize the retina, optic disc, and macula. Check intraocular pressure to rule out acute angle-closure glaucoma (where the eye will feel stony hard) and perform a confrontation visual field test.

Central Retinal Artery Occlusion (CRAO), Central Retinal Vein Occlusion (CRVO), Retinal Detachment, Giant Cell Arteritis (GCA), Vitreous Haemorrhage, Optic Neuritis, Acute Angle-Closure Glaucoma.

Scalp tenderness or jaw claudication (GCA), stony hard eye with nausea (Acute Glaucoma), 'curtain' or 'flashes and floaters' (Retinal Detachment), and sudden onset RAPD.

Initial bedside tests include visual acuity and pupillary assessment. Urgent bloods should include ESR and CRP if GCA is suspected, alongside a full blood count and glucose. Digital retinal photography or Optical Coherence Tomography (OCT) is often used in specialized units to detect macular oedema or detachment. Carotid artery doppler and ECG are required if an embolic source (like CRAO) is suspected. Urgent ophthalmic referral is mandatory for any acute, unexplained visual loss.

Amaurosis fugax is often described as a 'curtain falling over the eye' and warrants urgent TIA clinic referral if vision has returned. In CRAO, look for the 'cherry-red spot' on fundoscopy, representing the intact choroidal circulation seen through the pale, ischaemic retina. Always check the scalp for tenderness or jaw claudication in patients over 50 to screen for GCA; a missed diagnosis can lead to permanent bilateral blindness. Don't forget that vitreous haemorrhage is one of the most common causes of sudden loss in diabetics.

This topic maps to the 'Ophthalmology' and 'Emergency Medicine' sections of the MLA content map. Key focus areas for exams include the differentiation between painful and painless loss, the recognition of RAPD, and the immediate management of GCA with high-dose steroids to prevent contralateral loss.