RCGP SCA Algorithm — UK Primary Care
Acute visual loss is an ophthalmological emergency until proven otherwise. Speed matters — some causes have treatment windows of hours.
Central retinal artery occlusion is the ocular equivalent of a stroke — recanalization therapies (ocular massage, anterior chamber paracentesis, thrombolysis) have a treatment window of 4–6 hours after which retinal ischaemia becomes irreversible. Giant cell arteritis is the most common missed ocular emergency in primary care — starting prednisolone immediately (before biopsy) is correct because biopsy results remain positive for 2–4 weeks after starting steroids. Delaying by even 24 hours risks bilateral blindness.
The monocular vs binocular distinction is the most important early differentiator — covering each eye individually in consultation takes 10 seconds and separates ocular pathology from neurological pathology. New binocular diplopia in an elderly patient with hypertension strongly suggests microvascular cranial nerve palsy (III, IV, VI) — usually self-limiting but must exclude posterior communicating artery aneurysm (third nerve palsy with ptosis and dilated pupil = aneurysm until proven otherwise). Hydroxychloroquine maculopathy is preventable — annual eye checks should be confirmed at every review.
Dry eye disease is the most common cause of "blurry vision" in primary care — it accounts for 20% of all ophthalmology outpatient referrals and most do not need specialist review. A simple test: ask if vision improves after blinking — yes = dry eye/surface disease. AMD affects 600,000 people in the UK and is the leading cause of blindness in over-50s. Wet AMD requires urgent referral for intravitreal anti-VEGF (ranibizumab/aflibercept) — treatment within 2 weeks significantly improves visual outcome.
The pinhole test is the most underused tool in primary care — it can distinguish refractive error (improves with pinhole) from pathological visual loss (does not improve) in 30 seconds. RAPD is the key sign for optic nerve disease — it indicates asymmetric afferent input and is present in optic neuritis, CRVO, and CRAO. A complete third nerve palsy with a dilated pupil (surgical third nerve) must be differentiated from a pupil-sparing microvascular third nerve palsy — dilated pupil = aneurysm, emergency CT angiography required.
GCA bloods should be sent simultaneously with starting prednisolone — never delay treatment waiting for results. ESR can be normal in 10–20% of GCA, so CRP is essential alongside. In CRAO, 25% have an identifiable cardiac embolic source — AF is the most common; ECG and echocardiogram are part of the secondary prevention workup. Optic neuritis MRI demonstrates white matter lesions in 50% of patients at first episode — the MRI result determines the 10-year MS conversion risk and guides disease-modifying therapy decisions.
The RCOphth pathway for wet AMD requires treatment within 2 weeks — each week of delay loses approximately 1–2 lines of vision permanently. Anti-VEGF (ranibizumab, aflibercept) preserves or improves vision in 90% of wet AMD patients when treated promptly. Optometrist-led triage pathways (primary eyecare acute referral services, PEARS) are available in most NHS areas and can see urgent eye problems within 24–48 hours, freeing A&E and ophthalmology capacity for genuine emergencies.
In GCA, the risk of visual loss in the fellow eye without treatment is 30–50% within days — starting high-dose prednisolone before biopsy is the correct management. For diabetic macular oedema (the commonest cause of visual loss in working-age adults), HbA1c control is the most important intervention — each 1% HbA1c reduction reduces diabetic retinopathy progression by 25%. Intravitreal anti-VEGF for wet AMD costs ~£800/injection (6–12 per year) but preserves independence and prevents residential care — highly cost-effective NICE approval.
The AREDS2 trial (Age-Related Eye Disease Study 2) demonstrated that supplementation with lutein 10 mg + zeaxanthin 2 mg reduces AMD progression to advanced disease by 18–25% over 5 years. Diabetic eye screening is the most cost-effective preventive intervention in diabetes — each case of blindness prevented saves £70,000 in social care costs. The 22% of diabetic patients who do not attend screening have 3× higher rates of preventable visual impairment.
GCA steroid tapers are typically 18–24 months and require careful monitoring — relapse rate is 50% if steroids are stopped too quickly. Tocilizumab (IL-6 inhibitor) is now NICE-approved for relapsing/refractory GCA (TA518), allowing faster steroid taper and reducing cumulative steroid-related harm. AMD same-day emergency services (Macular Society) exist in most NHS regions — patients should have the service number. Pregnancy dramatically worsens diabetic retinopathy — women planning pregnancy should have pre-conception ophthalmology review and tightened glycaemic control.