Blurred vision

Blurred vision is loss of sharp focus — letters become fuzzy, edges fade, faces don't quite resolve. The differential splits cleanly: monocular (one eye) suggests a problem in front of (cornea, lens, vitreous) or at (retina, optic nerve) that eye specifically; binocular (both eyes) usually points to a refractive, neurological or systemic cause. Refractive issues (uncorrected myopia, hypermetropia, presbyopia, astigmatism) are by far the commonest cause and need an optometrist, not lab work. Systemic medical causes worth lab investigation: diabetes (hyperglycaemia transiently alters lens shape; chronic diabetes drives retinopathy), hypertension (hypertensive retinopathy, sudden severe hypertension), hypercalcaemia (corneal deposits, refractive shift), hyponatraemia (osmotic shift in lens), thyroid disease (Graves' eye), medications (steroids, hydroxychloroquine, sildenafil, anticholinergics). Sudden monocular blurring with pain or loss of part of the visual field is an ophthalmological emergency (retinal detachment, optic neuritis, central retinal artery occlusion).

• Uncorrected refractive error / new presbyopia — most common; optometrist.
• Diabetes (acute hyperglycaemia) — transient lens swelling; normalises with glucose control.
• Diabetic retinopathy — chronic; can be irreversible.
• Hypertension / hypertensive crisis — papilloedema, retinopathy.
• Cataract — gradual, worse at night.
• Dry-eye disease — blurring that clears with blinking.
• Macular degeneration — central vision distortion in older adults.
• Hypercalcaemia, severe hyponatraemia — refractive shift.
• Migraine aura — preceded by sparkly zigzags; recovers fully.
• Optic neuritis — pain on eye movement; often multiple sclerosis.
• Central retinal artery / vein occlusion, retinal detachment — sudden, severe, emergency.

First-line if no obvious refractive cause: fasting glucose + HbA1c, basic metabolic panel (sodium, calcium, potassium), blood pressure measurement, TSH if Graves' or hypothyroidism is suspected. Diabetic retinopathy needs an annual ophthalmologist eye exam — labs don't replace it. Mediora.AI surfaces the diabetic + hypertensive clusters; the eye itself needs in-person specialist evaluation.