Vision loss is one of the highest-stakes presentations in general practice. CRAO is the ocular equivalent of ischaemic stroke — emergent intervention within 4–6 hours (IOP-lowering, ocular massage, vascular interventions at specialist centres) may restore vision. Giant cell arteritis is the most preventable cause of permanent blindness in adults over 50 — starting high-dose corticosteroids immediately, before biopsy results, is correct management. Delay of even 24 hours risks bilateral permanent blindness. Retinal detachment involving the macula ("macula-off") carries a much worse visual prognosis — 90% surgical success if treated within 24 hours, dropping significantly beyond 72 hours. Amaurosis fugax is a TIA — 10% stroke risk in the next 48 hours without treatment.

The onset–laterality–type–pain framework localises the lesion before any examination. Sudden painless monocular loss = vascular occlusion until proven otherwise — act immediately. Central vision loss (inability to read, recognise faces) points to macular pathology. Peripheral vision loss (bumping into things, tunnel vision) points to glaucoma or retinitis pigmentosa — often asymptomatic until late. The distinction between a homonymous hemianopia (neurological, post-chiasmal) and monocular field defect (ocular, pre-chiasmal) is critical and requires careful testing of each eye separately. Always ask about metamorphopsia (straight lines appearing wavy) — this is the hallmark of macular disease and AMD conversion from dry to wet.

Anatomical localisation drives both urgency and referral destination. Anterior segment pathology (cornea, iris, lens) → urgent ophthalmology. Posterior segment (retina, choroid) → emergency ophthalmology for acute causes. Optic nerve (GCA, optic neuritis, glaucoma) → depends on cause: GCA = same day start steroids; optic neuritis = urgent neurology/ophthalmology; glaucoma = urgent outpatient. Neurological pathway (chiasm to cortex) → neurology, often with urgent MRI. Bitemporal hemianopia is pituitary adenoma until proven otherwise — urgent MRI pituitary. The RCGP SCA frequently presents visual field patterns that require anatomical localisation.

The RAPD (swinging light test) is the single most important GP examination finding for vision loss — it detects unilateral optic nerve or severe retinal dysfunction with high sensitivity and costs nothing. A positive RAPD with acute vision loss in a patient over 50 is GCA or CRAO until proven otherwise. Fundoscopy changes management in up to 25% of patients with acute vision loss — a pale disc with cherry-red spot = CRAO; a blurred disc = papilloedema (neurosurgical emergency). Documenting VA formally using Snellen is a medicolegal minimum — "vision seems reduced" is inadequate in a referral letter or if a complaint arises. Papilloedema (bilateral blurred disc margins, absent venous pulsation, haemorrhages) indicates raised ICP and requires same-day neurosurgery referral.

ESR and CRP must not delay steroids in suspected GCA — the principle of "treat first, investigate second" applies here unambiguously. Temporal artery biopsy remains positive for up to 2 weeks after starting steroids, so treatment does not invalidate biopsy. ESR is normal in approximately 10% of GCA — do not use a normal ESR to exclude GCA if clinical suspicion is present. For CRAO and amaurosis fugax, the TIA pathway provides rapid carotid imaging (to detect ipsilateral carotid stenosis requiring endarterectomy), cardiac monitoring (24h ECG for AF), and antiplatelet therapy. Hydroxychloroquine requires annual ophthalmological screening from year 5 of use (RCOphth 2018 guideline) — this is a GP prescribing responsibility to ensure monitoring is in place.

The referral urgency in vision loss is uniquely consequence-laden — a routine referral for a same-day condition can result in permanent blindness within hours. The 2WW pathway applies only to suspected intraocular malignancy (uveal melanoma). Everything else with acute vision loss is same-day or emergency. Cataract extraction has one of the lowest QALY costs in all of surgery — do not delay routine referral when VA is functionally impaired. The GP's most critical role in wet AMD is timely recognition and rapid referral — delay in initiating anti-VEGF directly correlates with worse visual outcome. Bilateral papilloedema on fundoscopy is a neurosurgical emergency requiring same-day CT head, not an optometrist referral.

Prednisolone for GCA must be started by the GP — this is the most time-critical prescribing decision in ophthalmic primary care. The contralateral eye loses vision in 30% of untreated GCA cases within days of the first affected eye. Starting steroids before biopsy is confirmed in NICE NG80 (GCA guideline 2023) as the correct approach. Anti-VEGF treatment has transformed wet AMD outcomes from inevitable progressive blindness to vision preservation or improvement in the majority — the GP's role is rapid recognition and referral, not watching and waiting. Never prescribe topical corticosteroid eyedrops in primary care without ophthalmological assessment — they can worsen undiagnosed herpetic keratitis (dendrite ulcer) and can permanently damage vision.

Smoking is the most important modifiable risk factor for AMD — a fact many patients are unaware of. Framing AMD risk as a smoking-related disease resonates more powerfully than generic health messages. AREDS2 supplementation has robust RCT evidence (NNT approximately 8 to prevent progression to advanced AMD over 5 years) and is cost-effective — it should be routinely discussed with AMD patients. The NHS Diabetic Eye Screening Programme is one of the most successful public health initiatives in the UK — it identifies and treats sight-threatening diabetic retinopathy before symptoms develop. GP practices should have recall systems ensuring all diabetic patients attend annual screening. Non-attendance is a significant clinical governance concern.

GCA steroid monitoring is a complex long-term primary care responsibility — relapses occur in up to 50% of patients during taper and require prompt steroid dose increase. The GP must ensure bone protection is in place from day 1 of steroid therapy (calcium, vitamin D, bisphosphonate) — long-term high-dose steroids cause osteoporosis in the majority without prophylaxis. Patient-held Amsler grids for AMD are one of the most cost-effective safety-netting tools in ophthalmic primary care — providing the card and explaining its use at every appointment takes 30 seconds and can save vision. The instruction "come back same day if lines look wavy" is the safety net that identifies wet AMD conversion before irreversible foveal damage occurs.