Emergency — Go to A&E Immediately for: Sudden painless loss of vision in one or both eyes, a curtain or shadow moving across your vision (retinal detachment), severe eye pain with blurred vision and nausea (acute angle closure glaucoma), flashes of light with new floaters, double vision of sudden onset, or visual loss after head trauma. These are ophthalmic emergencies that cannot wait.
Non-Urgent Medical Causes of Blurred Vision
| Cause | Test | How Vision is Affected |
|---|---|---|
| Diabetes mellitus | HbA1c, fasting glucose | Diabetic retinopathy — microaneurysms, haemorrhages, neovascularisation; lens swelling with blood sugar changes causes fluctuating blur |
| Hypertension | Blood pressure measurement; if severe: LFT, KFT | Hypertensive retinopathy — AV nicking, papilloedema in malignant hypertension; very high BP can cause sudden vision loss |
| Thyroid disease (Graves' ophthalmopathy) | TSH, Free T4, TSH receptor antibodies | Proptosis (bulging eyes), double vision, corneal exposure, optic nerve compression in severe cases |
| Anaemia | CBC, haemoglobin, ferritin | Severe anaemia reduces oxygen delivery to retina; can cause retinal haemorrhages in very low Hb |
| Migraine with aura | Clinical diagnosis; neurological exam | Typical visual aura (zigzag lights, scotoma) preceding headache; resolves within 60 minutes |
| Multiple sclerosis (optic neuritis) | MRI brain/spine, Visual Evoked Potentials (VEP), oligoclonal bands in CSF | Painful vision loss in one eye, central scotoma, reduced colour vision; pain on eye movement |
| Giant Cell Arteritis (age >50) | ESR (usually >50), CRP, temporal artery biopsy | Jaw claudication, scalp tenderness, sudden vision loss — ophthalmic emergency requiring urgent steroids |
Blood Tests for Blurred Vision
- HbA1c / Fasting glucose — Diabetes is the leading cause of preventable blindness in adults; essential test
- TSH — Graves' disease can cause significant eye involvement independent of thyroid hormone levels
- CBC / Haemoglobin — Severe anaemia affects retinal oxygen supply
- CRP and ESR — Elevated in giant cell arteritis (in patients over 50 with vision changes and headache)
- ANA and ANCA — Autoimmune causes of uveitis or retinal vasculitis
Always See an Ophthalmologist
Blood tests alone are insufficient for evaluating blurred vision. A proper eye examination by an ophthalmologist — including visual acuity, fundoscopy (looking at the retina), slit lamp examination, and intraocular pressure measurement — is essential to diagnose and monitor causes of vision change. Diabetic patients should have annual retinal screening photographs regardless of symptoms.
Questions to Ask Your Doctor
- Is my diabetes or blood pressure well enough controlled to protect my eyes?
- Should I be referred to an ophthalmologist for fundoscopy?
- If I have Graves' disease, do my eyes need specialist review?
- Given my age and symptoms, should we check ESR/CRP for giant cell arteritis?
- Am I due for retinal screening?
Medical Disclaimer: This information is for educational purposes only. Any sudden change in vision is a medical emergency. Always consult a doctor promptly for visual symptoms, and seek emergency care for sudden vision loss.