BPTBuddy

Red flags

Reduced visual acuity - never attribute to simple conjunctivitis
Severe pain, photophobia, ciliary flush - keratitis, uveitis, acute angle closure
Fixed mid-dilated pupil + severe pain + halos + vomiting - acute angle closure glaucoma (ophthalmic emergency)
Contact lens wearer with pain and red eye - microbial keratitis until excluded
History of trauma/high-velocity injury - open globe until excluded
Hypopyon - endophthalmitis or severe anterior uveitis

Diffuse redness, usually not vision-threatening

Conjunctivitis (viral > bacterial > allergic) - viral: watery discharge, preauricular node, highly contagious; bacterial: purulent discharge; allergic: itch, bilateral
Subconjunctival haemorrhage - painless, no visual change, resolves spontaneously
Episcleritis - mild discomfort, sectoral, self-limiting

Localised/vision-threatening

Keratitis (microbial, esp. contact lens-related; herpetic - dendritic ulcer on fluorescein) - pain, photophobia, reduced vision
Anterior uveitis/iritis - photophobia, ciliary flush, small/irregular pupil; associated with HLA-B27 spondyloarthropathies, sarcoidosis, IBD
Scleritis - severe boring pain, worse at night, associated with rheumatoid arthritis/vasculitis - vision-threatening
Acute angle closure glaucoma - severe pain, fixed dilated pupil, hazy cornea, markedly raised IOP
Endophthalmitis - post-surgical/traumatic, severe pain, hypopyon, vision loss

Pain severity, photophobia, discharge character, visual change
Contact lens use and hygiene, trauma, foreign body
Systemic disease - joint pain, back pain (spondyloarthropathy), IBD, prior episodes
Family/personal history of glaucoma, hypermetropia (angle closure risk)

Visual acuity first, always
Pattern of redness (diffuse vs ciliary flush/circumcorneal)
Pupil size/reactivity, corneal clarity, fluorescein staining (dendrite, ulcer, abrasion)
IOP if angle closure suspected (or clinical assessment if tonometry unavailable)
Anterior chamber - cells/flare (slit lamp), hypopyon

Fluorescein staining - dendritic ulcer (HSV keratitis), corneal defect
IOP measurement if glaucoma suspected
Swab for bacterial/viral culture if severe/atypical/neonatal conjunctivitis
Slit lamp examination (ophthalmology) for uveitis/keratitis/scleritis assessment

Any reduced acuity, severe pain, or ciliary flush - urgent ophthalmology referral, do not treat as simple conjunctivitis
Bacterial conjunctivitis: topical antibiotic (chloramphenicol), usually self-limiting even without treatment
Viral conjunctivitis: supportive, highly contagious - hygiene advice
Allergic conjunctivitis: topical antihistamine/mast cell stabiliser, avoid allergen
HSV keratitis: topical/oral aciclovir - topical corticosteroids contraindicated without antiviral cover (risk of corneal perforation)
Anterior uveitis: topical corticosteroid + cycloplegic (ophthalmology-directed), investigate for systemic association if recurrent/bilateral
Acute angle closure: emergency - IV acetazolamide, topical beta-blocker/pilocarpine, urgent ophthalmology for laser peripheral iridotomy
Microbial keratitis: urgent ophthalmology, intensive topical antibiotics (often fortified), stop contact lens use

Topical corticosteroids given for undiagnosed red eye can perforate a herpetic corneal ulcer - never start steroids without a slit lamp diagnosis
Contact lens wearers with red eye need urgent same-day assessment - bacterial keratitis (esp. Pseudomonas) can perforate within 24-48h
Angle closure glaucoma is easily missed if IOP/pupil exam is skipped in a patient presenting with "headache and vomiting"
Subconjunctival haemorrhage causes alarm out of proportion to its (benign) significance - but new/recurrent cases warrant a blood pressure and coagulation check

"Visual acuity and pupil exam come before I even think about a diagnosis - reduced acuity or an abnormal pupil changes everything."
"I never start a topical steroid on a red eye without a slit lamp and fluorescein first."

8 of 8 sections written · drafted 2026-09-13