Visual disturbance

"Eye patch" is a common cause of unilateral visual loss. Check your patient is not wearing an "eye patch" before examining. If you manage to remove it, you may cure the condition.

Epidemiology

Happens a lot. Go figure.

Differential Diagnosis

Visual loss is generally split up, at least with regards to a differential, in terms of time.

Acute (possibly)

These are the really important ones. If you don't identify them, then somebody might go blind - or die.

• Vascular causes - vein or artery
• Giant cell arteritis
• Retinal detachment
• Optic neuritis (ie. MS)
• TIA
• Closed-angle glaucoma

Not acute (probably)

• Diabetic retinopathy
• Cataract
• Wernicke's encephalopathy
• Macular degeneration
• Squint
• Amblyopia
• Cranial nerve palsies
• Optic tract disorders (inc. stroke)
• Papilloedema
• Hysterical visual loss - this is the least important thing you will ever learn about anything.

Clinical and Associated Features

Acute

• Retinal vein occlusion - painless unilateral visual loss like a "light dimming" or "shade coming down". Often noticed on waking. On fundoscopy: engorged veins; haemorrhage with 'cotton wool' exudates (infarcts); retinal oedema; swollen optic disc; new vessel proliferation; papilloedema; vitreous haemorrhage.
• Retinal artery occlusion - sudden visual loss in any possible field of vision. Uncommon but dangerous. Sudden, painless visual loss; poor direct light reflex, consensual is normal; pale and opaque retina; arteries pale, appear as red "threads"; fovea becomes "cherry red spot"; optic atrophy after a few weeks - optic disc goes white.
• Giant cell arteritis - headache, scalp tenderness, blurred/lost vision, fever
• Optic neuritis - inflammation of the optic nerve. Symptoms: variable central visual loss for 2-6 weeks; aching in region of the eye, aggravated by movement; central scotoma; loss of colour vision; relative afferent pupillary defect (RAPD); reduced visually-evoked response (a clever test)
• Closed-angle glaucoma - visual disturbance (leading to visual loss), eye pain (can be in the eye, around the orbit or just a generalised frontal headahce), nausea & vomiting. Often it's due to the pupil getting caught on the lens which blocks aqueous outflow. As such, it often happens when the pupil is mid-dilation e.g. during stress or excitement, watching TV in dim lighting, in patients on mydriatics.
• Wernicke's encephalopathy - if there's confusion and ataxia and the dude has a history of alcohol problems, think this.

Not acute

• Diabetic retinopathy - gradual visual deterioration; on fundscopy: microaneuryms, exudates, 'cotton wool' spots, haemorrhages, neovascularisation
• Age-related macular degeneration - gradual visual deterioration - usually starts with a central scotoma which gets bigger, causes difficulty with reading
• Cataracts - lens opacities. Gradual visual loss; difficulty reading, recognising faces, watching TV; diplopia (double vision)
• Papillloedema - bulging optic disc caused by raised ICP
• Squints - double vision, moving head to compensate
• Amblyopia/"lazy eye" - visual disturbance with no physical signs ("both the doctor and the patient see nothing")
• Optic tract disorders - this will usually be vascular or a tumour. Look for the visual defect
• Central nerve palsy - anything causing a palsy in nerves II, III, IV, V, VI could cause visual problems

Investigations

Generally, there are clever eye tests like visually-evoked responses and badass opthalmoscopy using clever machines but nothing particular.