About This Page
This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
The Bottom Line
- Acute vision loss is an emergency until proven otherwise — document visual acuity, visual fields, pupils, pain, and laterality
- Painless monocular loss suggests retinal/vascular disease; painful loss suggests optic neuritis, glaucoma, keratitis, uveitis, or trauma
- Central retinal artery occlusion and amaurosis fugax are stroke-equivalent vascular events requiring urgent stroke-style assessment
- Giant cell arteritis must be treated immediately with corticosteroids when suspected — do not wait for biopsy
- Flashes, floaters, and curtain-like field defect suggest retinal detachment and require urgent ophthalmology
Approach to the Presentation
Acute vision loss should be approached using three axes: monocular versus binocular, painful versus painless, and visual acuity versus visual field. Monocular symptoms usually localize anterior to the optic chiasm: cornea, anterior chamber, lens, retina, optic nerve. Binocular homonymous field loss suggests retrochiasmal neurologic disease such as stroke. Ask about onset, duration, transient versus persistent loss, curtain/shadow, flashes/floaters, headache, scalp tenderness, jaw claudication, eye pain, pain with eye movement, trauma, vascular risk factors, atrial fibrillation, autoimmune disease, and neurologic symptoms. The initial examination is visual acuity, pupils/RAPD, fields by confrontation, fundus if possible, red eye/corneal assessment, intraocular pressure when safe, and neurologic exam.
Differential Diagnosis
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Central Retinal Artery Occlusion / Branch Retinal Artery Occlusion | must-not-miss | Sudden painless monocular vision loss, afferent pupillary defect, pale retina, cherry-red spot in CRAO; vascular risk factors or embolic source | Fundoscopy/OCT; urgent stroke work-up including carotid and cardiac evaluation |
| Giant Cell Arteritis with Arteritic AION | must-not-miss | Age >50, new headache, scalp tenderness, jaw claudication, polymyalgia rheumatica symptoms, transient or permanent vision loss | ESR/CRP/platelets; temporal artery ultrasound/biopsy — treat immediately before confirmation |
| Retinal Detachment | must-not-miss | Flashes, floaters, curtain/shadow over visual field, painless field loss; risk with high myopia, trauma, previous surgery | Dilated fundus exam; ocular ultrasound if fundus not visible |
| Acute Angle-Closure Glaucoma | must-not-miss | Painful red eye, blurred vision, halos, headache, nausea/vomiting, mid-dilated fixed pupil, cloudy cornea | Elevated intraocular pressure; urgent ophthalmology |
| Stroke / TIA involving Visual Pathways | must-not-miss | Binocular homonymous field loss, diplopia, dysarthria, weakness, ataxia, cortical blindness; vascular risk factors | Urgent neuroimaging and stroke protocol assessment |
| Optic Neuritis | common | Young adult, subacute monocular vision loss, pain with eye movement, reduced colour vision, RAPD; associated with MS or other demyelinating disease | MRI brain/orbits with gadolinium; visual evoked potentials selectively |
| Vitreous Haemorrhage | common | Sudden painless floaters/haze or vision loss, diabetic retinopathy, retinal tear, trauma, anticoagulation | Fundoscopy if view possible; ocular ultrasound if view obscured |
| Retinal Vein Occlusion | common | Sudden painless monocular vision loss, vascular risk factors; fundus shows haemorrhages and dilated tortuous veins | Dilated fundus exam/OCT; assess vascular risk factors |
| Migraine Aura | common | Transient positive visual symptoms (scintillations, zig-zags), gradual spread over minutes, often binocular, resolves within 60 minutes ± headache | Clinical diagnosis after excluding first episode, vascular, retinal, or neurologic red flags |
| Corneal Abrasion / Keratitis / Uveitis | common | Painful red eye with photophobia and blurred vision; fluorescein staining or anterior chamber findings may be present | Slit lamp and fluorescein; IOP when appropriate |
| Functional / Non-organic Visual Loss | rare | Inconsistent examination, normal pupils/fundus, non-anatomic field loss; diagnosis of exclusion | Normal objective examination after urgent pathology excluded |
Red Flags & Key History
Symptoms
Sudden painless monocular loss — retinal artery occlusion, retinal detachment, vitreous haemorrhage, retinal vein occlusion
Age >50 with new headache, jaw claudication, scalp tenderness, or PMR symptoms — giant cell arteritis
Flashes, floaters, or curtain/shadow — retinal tear or detachment
Painful red eye with halos, nausea, vomiting — acute angle-closure glaucoma
Pain with eye movement and loss of colour vision — optic neuritis
Binocular field loss, diplopia, weakness, dysarthria, ataxia — stroke/TIA
Transient monocular curtain lasting minutes — amaurosis fugax, embolic warning sign
Signs
Relative afferent pupillary defect — optic nerve or severe retinal disease
Cherry-red spot or pale retina — central retinal artery occlusion
Optic disc oedema with haemorrhages — arteritic or non-arteritic AION
Homonymous hemianopia — retrochiasmal stroke pathway
Elevated IOP with mid-dilated pupil — acute angle closure
Reduced red colour saturation — optic neuritis clue
Approach to Investigation
First-line
Visual acuity, pupils, visual fieldsDocument acuity in each eye, RAPD, confrontation fields, colour desaturation, and pain. These localize the lesion and determine urgency
Fundoscopy / dilated retinal examinationLook for retinal detachment, haemorrhage, CRAO cherry-red spot, optic disc oedema, retinal vein occlusion, diabetic retinopathy
Intraocular pressureMeasure when acute glaucoma suspected and globe rupture is not suspected
ESR, CRP, plateletsImmediate blood tests if giant cell arteritis is possible; normal results do not fully exclude if clinical suspicion is high
Second-line
Ocular ultrasoundUseful when fundus view is obscured by vitreous haemorrhage or cataract; can identify retinal detachment
OCT / retinal imagingOphthalmology-led confirmation of macular, retinal vascular, or optic nerve pathology
Stroke work-upFor CRAO, amaurosis fugax, or neurologic field loss: urgent neuroimaging, carotid imaging, ECG, rhythm monitoring, echocardiography where indicated
MRI brain/orbitsFor optic neuritis, demyelination, compressive optic neuropathy, or retrochiasmal lesions
Specialist
Urgent ophthalmologyMost acute monocular visual loss, suspected detachment, CRAO, GCA eye symptoms, glaucoma, keratitis, uveitis, trauma, or vitreous haemorrhage
Stroke team / emergency medicineCRAO, amaurosis fugax, homonymous field deficit, or other acute neurologic symptoms should be managed through acute vascular pathways
Management Principles
MCC Objective 115-1 + Canadian ophthalmology and stroke-style emergency practice1
Immediate principles
- Treat acute vision loss as time-critical; document acuity and pupils and seek urgent ophthalmology or stroke input depending on localization
- Do not send home a patient with new objective vision loss without a clear diagnosis and urgent follow-up plan
- Protect the eye and avoid pressure if trauma or globe rupture is possible
2
Vascular and inflammatory emergencies
- Suspected GCA with visual symptoms: start high-dose corticosteroids immediately; do not wait for temporal artery biopsy/ultrasound
- CRAO/amaurosis fugax: manage as vascular emergency; urgent stroke work-up and secondary prevention
- Retinal vein occlusion: urgent ophthalmology; address hypertension, diabetes, lipids, smoking, and thrombosis risk where appropriate
3
Retinal detachment and vitreous haemorrhage
- Retinal detachment: urgent ophthalmology; timing depends on macula-on vs macula-off status but should not be delayed
- Vitreous haemorrhage: ophthalmology assessment and ultrasound if fundus cannot be visualized; treat underlying retinal tear/diabetic disease
4
Painful ocular causes
- Acute angle-closure glaucoma: urgent IOP-lowering therapy and ophthalmology for definitive laser/surgical management
- Optic neuritis: MRI brain/orbits and neurology/ophthalmology input; IV steroids may speed recovery in selected cases
- Keratitis/uveitis: ophthalmology-directed therapy; avoid empiric topical steroids in undifferentiated cases
Complications & Pitfalls
- Assuming visual loss is ocular: Homonymous field defects are neurologic until proven otherwise.
- Delaying GCA steroids: Waiting for biopsy can cost vision in the other eye.
- Missing CRAO: Sudden painless monocular loss is a stroke-equivalent presentation requiring urgent vascular assessment.
- Calling retinal detachment migraine: Curtain-like field loss and new floaters/flashes require retinal assessment.
- Failure to document acuity: Visual acuity is essential for triage, referral urgency, and medicolegal clarity.
MCCQE1 Exam Tips
- 1Monocular vision loss localizes to the eye/optic nerve; binocular homonymous field loss localizes behind the chiasm
- 2GCA stem: older patient + new headache + jaw claudication + vision symptoms. Give steroids now, biopsy later
- 3CRAO stem: sudden painless monocular loss + cherry-red spot. Think embolic/stroke work-up
- 4Retinal detachment stem: flashes + floaters + curtain descending over vision
- 5Optic neuritis stem: young adult + pain with eye movement + decreased colour vision + RAPD
- 6Acute angle closure stem: painful red eye + halos + nausea/vomiting + high IOP
- 7Migraine aura usually has positive visual phenomena and gradual spread; first-ever or atypical aura still needs careful exclusion of vascular disease
practicetest your knowledge on acute vision lossApply what you've learnt with MCCQE1-style questions from the iatroX Q-Bank — ent & ophthalmologic and beyond.
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