A subconjunctival haemorrhage (SCH) is almost always a benign, self-limiting condition — the haemorrhage represents bleeding into the potential space between the conjunctiva and the underlying sclera, caused by rupture of a small conjunctival blood vessel. The blood is bright red initially, may spread and darken over days, and resolves completely within 2-4 weeks without treatment. The critical clinical task for GPs is not to manage the SCH itself, but to identify the rare cases where it is a sign of serious underlying pathology. The most important distinguishing feature: in simple SCH, visual acuity is completely normal. Any reduction in visual acuity in the presence of a red eye is not a simple SCH — it requires urgent ophthalmology assessment. The posterior limit of a benign SCH should be visible (the blood does not extend beyond the equator of the globe) — if you cannot see the posterior border, a ruptured globe or posterior injury must be excluded.

The hypertension-subconjunctival haemorrhage association deserves special attention — hypertension is a well-established risk factor for SCH, and a patient who presents with a first SCH without clear precipitating cause should have their blood pressure checked at the same consultation. The mechanism: chronic hypertension causes hyaline degeneration of small vessel walls (arteriosclerosis), making the conjunctival capillaries more fragile and prone to spontaneous rupture even with minor physiological triggers (rising from sleep, morning coughing). The practical approach: any patient with a first SCH and no clear cause → check BP. If BP is elevated: this is an opportunity to diagnose and treat hypertension. If hypertension is already known and treated: check medication adherence and BP control. This does not mean that SCH itself requires hypertension treatment urgently — the SCH will resolve regardless — but it is a diagnostic opportunity not to be wasted.

The afferent pupillary defect (APD) is the single most important examination finding that distinguishes serious posterior segment pathology from a benign superficial haemorrhage. The swinging flashlight test: in a dim room, swing a bright pen torch from one eye to the other. Normal: both pupils constrict when light is directed at them. RAPD (relative afferent pupillary defect): when the torch swings from the normal eye to the affected eye, the pupils paradoxically dilate rather than constrict — this indicates that the optic nerve input from the affected eye is weaker than from the normal eye (the brain compares the two signals). An RAPD in the context of a red eye or SCH after trauma indicates: retinal detachment, vitreous haemorrhage, traumatic optic neuropathy, or posterior rupture of the globe — all requiring emergency ophthalmology assessment. The swinging flashlight test takes approximately 30 seconds and should be performed for every patient presenting with a red eye — it is a key component of the red eye assessment that GPs should be confident performing.

The management of anticoagulation in patients with SCH is an important prescribing decision — stopping anticoagulation for an SCH exposes the patient to the very thromboembolic risks that the anticoagulation was prescribed to prevent (stroke, DVT/PE, valve thrombosis). An SCH is a minor, self-limiting, cosmetically unpleasant but clinically inconsequential event that does not warrant suspension of anticoagulation. The correct approach: check the INR (if on warfarin) or assess DOAC adherence; if INR is supratherapeutic, adjust the warfarin dose; document the SCH as a minor bleeding event in the anticoagulation record; continue anticoagulation. The only bleeding events that should prompt consideration of anticoagulation interruption are: intracranial haemorrhage, massive GI bleeding, life-threatening haemorrhage from any site. An SCH does not meet these criteria.

The GP has a valuable reassurance opportunity at every SCH consultation — the haemorrhage looks alarming to patients (bright red, spreading, covering the white of the eye) and causes significant anxiety. Effective reassurance: 'A subconjunctival haemorrhage is like a bruise on the skin — it looks worse than it is. It is caused by a tiny blood vessel on the surface of the eye breaking. It will gradually change colour from red to orange to yellow, and completely disappear over the next 2-3 weeks without any treatment. It does not affect your vision and will not damage your eye.' Managing expectations: the colour change and spreading over the first few days can be alarming — tell the patient in advance that the haemorrhage may look larger or darker over days 2-5 before it begins to resolve. Cold compresses in the first 24 hours reduce spreading; artificial tear lubricant drops (if the eye is dry and uncomfortable) can provide symptomatic relief. No eye drops, tablets, or other specific treatment is needed.

The post-intravitreal injection SCH management is worth specific inclusion because anti-VEGF therapy for wet AMD, diabetic macular oedema, and retinal vein occlusion is now extremely common — the UK administers approximately 1 million intravitreal injections per year. After each injection, a small SCH at the injection site is expected and normal (the needle punctures the conjunctiva). Patients who are treated monthly or bimonthly may contact their GP about the red eye post-injection, and GPs must know to reassure rather than alarm. However: any SCH that develops in a different location from the injection site, or is associated with reduced vision or pain, should be referred back to the ophthalmology team. The key information GPs need to provide: 'This red patch near where you had your injection is completely normal — it is just a tiny bruise on the surface of the eye from the needle. It will disappear in 1-2 weeks and does not affect how well your eye injection is working.'

Non-accidental injury should be considered in the differential when a child presents with a subconjunctival haemorrhage without a clearly consistent mechanism — retinal haemorrhages (not visible to the GP without ophthalmoscopy) are a classical feature of abusive head trauma ('shaken baby syndrome'), and conjunctival haemorrhages can co-exist. Any child presenting with an SCH where: the mechanism is unclear or inconsistent with the injury, there are other unexplained bruises or injuries, the parent's account is inconsistent, or the child's behaviour is abnormal — should trigger a safeguarding assessment. Document the exact mechanism as described by the parent/guardian. Refer to paediatrics for full assessment if non-accidental injury is suspected. The medicolegal documentation standard: 'Mechanism of injury as described by parent: [exact statement]. Injury consistent/inconsistent with mechanism. Safeguarding concern: [yes/no and reasoning]. Action taken: [specify].'

The obstetric Valsalva SCH is worth specific mention because of its high frequency and because it causes significant maternal anxiety if not proactively addressed — studies report SCH in approximately 4-8% of vaginal deliveries, and the rate is higher after prolonged second-stage labour. Midwives and obstetricians should ideally mention the possibility of SCH in antenatal education so that mothers are not alarmed when they look in the mirror post-delivery. GPs who see post-natal women for the 6-week check should ask about any eye symptoms and reassure about SCH if present. The condition is benign and self-limiting, but a new mother who notices 'a lot of blood in her eye' without prior warning may experience significant anxiety and seek emergency care unnecessarily.

The documented visual acuity measurement is medicolegally essential for every red eye consultation in primary care — the GMC Good Medical Practice standards require that clinical assessments are thorough and appropriate to the presenting condition. In a patient with a red eye, VA measurement is a basic and mandatory component of the assessment. A GP who documents 'vision normal' without measuring VA, and whose patient subsequently has a missed retinal detachment or posterior segment injury, faces a defensible medico-legal challenge only if they can demonstrate that VA was formally measured and recorded. The documentation standard: 'VA: Right 6/6 (or 'reads news print at 30 cm'). Left 6/6. Posterior border of haemorrhage visible. Pupils equal and reactive. No RAPD. Diagnosis: simple SCH. Management and safety-net provided.'