What Is Causing My Red Eye?

"Red eye" is a finding, not a diagnosis: it simply means blood vessels on or in the eye are dilated or have leaked. The useful information is in the details — where the redness sits, whether it hurts, whether light bothers you, what the discharge looks like, and whether vision has changed. Those few observations separate the causes that need reassurance from the ones that need drops today or an emergency room tonight.

Reading the red eye by its pattern:

• Diffuse pink with watery or sticky discharge: conjunctivitis — viral, bacterial, or allergic (allergy itches and involves both eyes).
• A single, sharply outlined patch of solid red on the white: subconjunctival hemorrhage — a broken capillary, painless, resolves like a bruise in one to two weeks.
• Redness with burning and crusty lid margins, worse on waking: blepharitis and dry eye — chronic, manageable, not contagious.
• A ring of redness concentrated around the colored iris, with aching pain and light sensitivity: iritis (inflammation inside the front of the eye).
• Redness with severe pain and light sensitivity in a contact lens wearer, sometimes with a white corneal spot: keratitis or a corneal ulcer — sight-threatening and time-sensitive.
• Deep, boring pain with a violaceous, tender redness of the eye wall: scleritis, frequently tied to autoimmune disease.
• A hard, red, painful eye with halos, headache, and nausea: acute angle-closure glaucoma — an emergency measured in hours.

One red eye lasting weeks without an obvious explanation also deserves an exam, since inflammation and, rarely, growths can present that way.

Seek same-day care — (717) 637-1919, or emergency care after hours — for a red eye with any of the following:

• Moderate to severe pain, or pain that wakes you at night
• Marked light sensitivity or blurred vision
• Halos around lights, severe headache, or nausea
• A white or cloudy spot on the cornea
• Contact lens wear
• Recent trauma, chemical exposure, or eye surgery
• A fixed or unusual pupil, or redness with a bulging eye or fever

Vision, pupils, and eye pressure come first — they catch the emergencies. The slit-lamp exam then localizes the redness: conjunctiva only, cornea (highlighted with fluorescein dye), the front chamber (cells of iritis), or the deeper sclera. The history — lens wear, allergy, cold symptoms, medications, autoimmune disease — usually completes the diagnosis. Most red eyes need no testing beyond this; the exam's real job is making sure the dangerous causes are not hiding behind a pink one.

Treatment tracks the cause: artificial tears and lid hygiene for dry eye and blepharitis; antihistamine drops for allergy; clinician-directed care for bacterial conjunctivitis (mild cases often resolve without antibiotics; drops are prescribed when indicated); time and hygiene for viral pink eye; nothing but patience for a subconjunctival hemorrhage. The serious causes get urgent, specific therapy — intensive antimicrobial drops for corneal infection, anti-inflammatory treatment for iritis and scleritis, and immediate pressure-lowering treatment plus laser for angle-closure. Redness-relief drops whiten the eye without treating anything and can rebound; they are not a treatment.

• Do not mask redness with decongestant drops while a cause goes undiagnosed.
• Do not use leftover prescription drops, especially steroids, without an exam.
• Do not keep wearing contact lenses in a red eye.
• Do not rub the eye.
• Do not wait on pain, light sensitivity, vision change, halos, or nausea — those combinations are urgent.