The majority of patients with acute red eye have a relatively benign condition, such as bacterial, viral, or allergic conjunctivitis, subconjunctival hemorrhage, or blepharitis, which poses little or no threat to vision. Conversely a few are at risk of rapid progression within a few hours or days to severe visual impairment, even blindness, such as from acute angle-closure glaucoma, intraocular infection (endophthalmitis), bacterial, viral, amebic, or fungal corneal infection, acute uveitis, or scleritis.
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Conjunctivitis—Conjunctival injection, eye discharge, gritty or uncomfortable feeling, and no vision loss (Figures 27-1, 27-2, 27-3, 27-4) (see also Chapter 18, Conjunctivitis).
Episcleritis—Segmental or diffuse inflammation of episclera (pink color), mild or no discomfort, but can be tender to palpation, and no vision disturbance (Figure 27-5) (see also Chapter 19, Scleritis and Episcleritis).
Scleritis—Segmental or diffuse inflammation of sclera (dark red, purple, or blue color), severe boring eye pain often radiating to head and neck, and photophobia and vision loss (Figure 27-6) (see also Chapter 19, Scleritis and Episcleritis).
Keratitis or corneal ulcerations—Diffuse erythema with ciliary injection often with pupillary constriction; eye discharge; and pain, photophobia, vision loss depending on the location of ulceration (Figure 27-7). Often associated with the use of contact lenses.
Subconjunctival hemorrhage (Figure 27-8)—Bright red subconjunctival blood; usually not painful; can present after significant coughing/sneezing, after trauma, or in the setting of dry eyes with minor trauma from rubbing with a finger. Not vision-threatening.
Ocular rosacea—Eye findings present in more than 50% of people with facial rosacea. Can present as blepharitis, conjunctivitis, or episcleritis or cause corneal ulcerations and neovascularization (Figures 27-9 and 27-10).
Uveitis or iritis—A 360-degree injection, which is most intense at the limbus, eye pain, photophobia, and vision loss (Figure 27-11) (see also Chapter 20, Uveitis and Iritis).
Trauma causing globe injury, or hemorrhage into the anterior chamber called hyphema (Figures 27-12 and 27-13) (see Chapter 26, Eye Trauma—Hyphema).
Pterygium—Fibrovascular tissue on the surface of the eye extending onto the cornea (Figure 27-14) (see also Chapter 14, Pterygium).
Hypopyon is a term for visible white cells (pus) layered out in the anterior chamber. It may be caused by inflammation of the iris or an eye infection. The inflammation and/or infection also causes the conjunctiva and sclera to become red (Figure 27-15).
Acute-angle closure glaucoma—Cloudy cornea and scleral injection, shallow anterior chamber (check other eye if difficult to assess chamber depth in the red eye), eye pain with ipsilateral headache, and severe vision loss (see also Chapter 21, Glaucoma).
Eyelid pathology—Blepharitis (inflammation of the eyelid) (Figure 27-16). Entropion is a turning inward of the eyelid and can cause irritation to the conjunctiva and cornea.