Red eye

Gritty pain suggests external cause. Aching pain suggests internal cause. Light sensitivity always accompanies inflammation in the eye. Fluoresceine (Fl) yellow dye glows green with a blue examination light and stains all epithelial breaks.

Some differential diagnoses and typical outline evidence

Spontaneous sub-conjunctival haemorrhage	Suggested by: painless bright red area on conjunctiva (oxygenated blood) and no light sensitivity.
	Confirmed by: clinical appearance and resolution over days. No Fl staining of cornea (not done often).
	Management: OHCS p432.
Conjunctivitis due to bacterial infection	Suggested by: red eyes, dilated blood vessels on the eyeball and the tarsal (lid) conjunctiva with a purulent discharge ± bilateral ± gritty pain.
	Confirmed by: above clinical appearance. Not light sensitive and no Fl stain of cornea.
	Management: OHCS p432.
Conjunctivitis due to viral infection	Suggested by: red eyes with dilated vessels on the eyeball only, sometimes in one quadrant around the cornea with a watery ‘tap running’ discharge. Gritty pain ± impaired vision.
	Confirmed by: Fl stain showing dendritic (branching) pattern and resolution with topical antiviral.
	Management: OHCS p432.
Conjunctivitis due to allergy	Suggested by: red eyes with pink swollen conjunctiva and white stringy mucoid discharge.
	Confirmed by: no Fl stain and no visual loss and resolution with chromoglycate (over six weeks) or steroid eye drops.
	Management: OHCS p432.
Corneal ulcer (ulcerative keratitis) due to abrasion or Herpes simplex, Pseudomonas, Candida, Aspergillus, protozoa	Suggested by: painful, light-sensitive, deeply red eye with yellowish abscess in the cornea. Purulent discharge.
	Confirmed by: slit lamp examination after fluorescein instillation showing hypopyon (pus in the eye).
	Management: OHCS p432.
Episcleritis	Suggested by: localised red eye with superficial vessel dilatation. Mild pain. No visual loss or light sensitivity.
	Confirmed by: Instillation of one drop of phenylephrine 2.5% causing a blanching of the lesion.
	Management: OHCS p432.
Scleritis	Suggested by: localised area of dark red dilated superficial and deep vessel on the sclera with aching pain and tenderness.
	Confirmed by: failure to blanche with one drop of 2.5% phenylephrine.
	Management: OHCS p432.
Acute closed-angle glaucoma (emergency)	Suggested by: severely painful red eyeball with marked visual loss, accompanied by nausea and vomiting ± history of haloes around lights and severe headache with blurred vision.
	Confirmed by: dull grey cornea, non reacting and irregular pupil with raised ocular pressures.
	Management: OHCS p430.
Iritis or uveitis (see page 264)	Suggested by: redness around cornea and haze in front of iris and severe light sensitivity (photophobia).
	Confirmed by: small non-reacting and irregular pupil. Slit lamp examination showing flare, cells and hypopyon (pus in eye).
	Management: OHCS p430.