Red Eye: A Clinical Approach
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Direct answer
Not every red eye deserves antibiotic drops. A red eye with normal vision, a clear cornea and no photophobia is almost always conjunctivitis; reduced vision, ciliary pain, photophobia, corneal opacity, a fixed or mid-dilated pupil or a stony-hard eye mark the dangerous causes — keratitis, anterior uveitis and acute angle-closure glaucoma. The single discriminant AK Khurana drills is conjunctival versus ciliary congestion: bright red, superficial, movable vessels that branch and are maximal in the fornices, against a dusky violet, deep, immobile circumcorneal flush with ciliary tenderness. Management flows from that split.
What you must remember
- Conjunctival congestion: bright red, superficial vessels that move with the conjunctiva, maximal away from the limbus, mucoid or purulent discharge, vision normal — bacterial, viral or allergic conjunctivitis.
- Ciliary congestion: violet-red, deep circumcorneal vessels that do not move, with ciliary tenderness (pain on pressing over the ciliary body through the depressed lid) — keratitis, iritis or acute congestive glaucoma.
- Danger signs demanding same-day referral: vision below 6/18, severe pain, photophobia, corneal opacity or epithelial defect, hypopyon, keratic precipitates, a vertically oval fixed mid-dilated pupil, or raised intraocular pressure.
- Acute angle-closure glaucoma: halos around lights, steamy oedematous cornea, fixed semi-dilated pupil, intraocular pressure often 40–60 mmHg, hard globe; emergency treatment is intravenous acetazolamide with mannitol, topical pilocarpine once pressure falls, then Nd:YAG laser iridotomy.
- Iritis (anterior uveitis): ciliary flush, small irregular pupil, keratic precipitates, flare and cells in the anterior chamber, synechiae; treated with cycloplegics and topical corticosteroids.
- Discharge as a clue: mucopurulent in bacterial, watery with follicles and preauricular node in adenoviral, stringy with itching in allergic; hyperacute profuse purulent discharge with chemosis means gonococcal conjunctivitis — an ocular emergency.
- A red eye in a contact lens wearer is microbial keratitis until proved otherwise; stop the lens, stain with fluorescein, refer.
Four red eyes at the slit lamp
Walk through four casualty arrivals and the pattern fixes itself. The first is a young man with bilateral watery redness, follicles in the lower fornix and a tender preauricular node — adenoviral follicular conjunctivitis; support with lubricants, warn about contagion for two weeks, no antibiotic needed. The second is a farmer with pain, photophobia and a white infiltrate that stains with fluorescein — a corneal ulcer; scrape before starting fortified antibiotics, because agricultural trauma in India is fungal until excluded. The third is a middle-aged woman with halos, a hazy cornea and a fixed vertically oval pupil at 50 mmHg — acute angle closure; bring the pressure down medically, then iridotomy, and prophylactic iridotomy in the fellow eye. The fourth has one ciliary-flushed eye, a small pupil, one-plus cells and flare and fine keratic precipitates — anterior uveitis; dilate with homatropine, start topical steroids after considering infection, and hunt the cause, tuberculosis first in India.
Where students slip
Two errors dominate. The first is prescribing a steroid–antibiotic combination from the pharmacy for any red eye: in herpetic epithelial disease it converts a dendrite into a geographic ulcer, and unsupervised use raises intraocular pressure. The second is labelling acute angle closure as "severe conjunctivitis" because the cornea is hazy and vision poor — checking the pupil size and pressing the globe would have separated the two instantly. Examiners love a photograph of a ciliary flush with the question "which vessel layer, and what three diagnoses does it narrow to?"
Frequently asked questions
How do you differentiate conjunctival from ciliary congestion?
Conjunctival congestion is bright red, superficial, maximal in the fornices and movable with the conjunctiva; ciliary congestion is violet, deep, maximal at the limbus, immobile and accompanied by ciliary tenderness, pointing to keratitis, iritis or acute glaucoma.
Which red eye presentations are true emergencies?
Acute angle-closure glaucoma, sight-threatening keratitis or corneal ulcer, gonococcal (hyperacute purulent) conjunctivitis, endophthalmitis and orbital cellulitis all need same-day specialist care.
What pupil findings localise a red eye?
A fixed, vertically oval, mid-dilated pupil suggests acute angle closure; a small, irregular, poorly dilating pupil with synechiae suggests anterior uveitis; a dilated pupil with corneal haze and severe pain suggests raised pressure or iris ischaemia.
Why are topical steroids dangerous in an undiagnosed red eye?
They worsen herpes simplex epithelial keratitis, favour fungal and bacterial multiplication, cause steroid-induced glaucoma and cataract, and mask progression — reserve them for proven non-infectious inflammation under supervision.
What is ciliary tenderness and what does it indicate?
Pain on gentle pressure over the ciliary body region through the closed lid, indicating inflammation of the deeper coats — uveitis, keratitis or glaucoma — rather than surface conjunctival disease.
Which red eye presents with preauricular lymphadenopathy?
Adenoviral follicular conjunctivitis (pharyngoconjunctival or epidemic keratoconjunctivitis) classically, and also gonococcal, chlamydial and Parinaud oculoglandular conjunctivitis.