Red eye (medicine)

A red eye is an eye that appears red due to illness or injury. It is usually injection and prominence of the superficial blood vessels of the conjunctiva, which may be caused by disorders of these or adjacent structures. Conjunctivitis and subconjunctival hemorrhage are two of the less serious but more common causes.

Red eye
Subconjunctival hemorrhage causing red coloration as result of ruptured blood vessel in the eye.

Management includes assessing whether emergency action (including referral) is needed, or whether treatment can be accomplished without additional resources.

Slit lamp examination is invaluable in diagnosis but initial assessment can be performed using a careful history, testing vision (visual acuity), and carrying out a penlight examination.


hyphaema – showing blood filling the anterior chamber, causing a horizontal fluid level.

Particular signs and symptoms may indicate that the cause is serious and requires immediate attention.[1]

Six such signs are:

  • reduced visual acuity
  • ciliary flush (circumcorneal injection)
  • corneal abnormalities including edema or opacities ("corneal haze")
  • corneal staining
  • abnormal pupil size
  • abnormal intraocular pressure

The most useful is a smaller pupil in the red eye than none red eye and sensitivity to bright lights.[2]

Visual acuity

A reduction in visual acuity in a 'red eye' is indicative of serious ocular disease,[3] such as keratitis, iridocyclitis, and glaucoma, and never occurs in simple conjunctivitis without accompanying corneal involvement.

Ciliary flush

Ciliary flush is usually present in eyes with corneal inflammation, iridocyclitis or acute glaucoma, though not simple conjunctivitis. A ciliary flush is a ring of red or violet spreading out from around the cornea of the eye.

Corneal abnormalities

The cornea is required to be transparent to transmit light to the retina. Because of injury, infection or inflammation, an area of opacity may develop which can be seen with a penlight or ophthalmoscope. In rare instances, this opacity is congenital.[4] In some, there is a family history of corneal growth disorders which may be progressive with age. Much more commonly, misuse of contact lenses may be a precipitating factor. Whichever, it is always potentially serious and sometimes necessitates urgent treatment and corneal opacities are the fourth leading cause of blindness. Opacities may be keratic, that is, due to the deposition of inflammatory cells, hazy, usually from corneal edema, or they may be localized in the case of corneal ulcer or keratitis.
Corneal epithelial disruptions may be detected with fluorescein staining of the eye, and careful observation with cobalt-blue light. Corneal epithelial disruptions would stain green, which represents some injury of the corneal epithelium. These types of disruptions may be due to corneal inflammations or physical trauma to the cornea, such as a foreign body.

Pupillary abnormalities

In an eye with iridocyclitis, (inflammation of both the iris and ciliary body), the involved pupil will be smaller than the uninvolved, due to reflex muscle spasm of the sphincter muscle of the iris. Generally, conjunctivitis does not affect the pupils. With acute angle-closure glaucoma, the pupil is generally fixed in mid-position, oval, and responds sluggishly to light, if at all.

Shallow anterior chamber depth may indicate a predisposition to one form of glaucoma (narrow angle) but requires slit-lamp examination or other special techniques to determine it. In the presence of a "red eye", a shallow anterior chamber may indicate acute glaucoma, which requires immediate attention.

Abnormal intraocular pressure

Intraocular pressure should be measured as part of the routine eye examination. It is usually only elevated by iridocyclitis or acute-closure glaucoma, but not by relatively benign conditions. In iritis and traumatic perforating ocular injuries, the intraocular pressure is usually low.

Severe pain

Those with conjunctivitis may report mild irritation or scratchiness, but never extreme pain, which is an indicator of more serious disease such as keratitis, corneal ulceration, iridocyclitis, or acute glaucoma.

Differential diagnosis

Of the many causes, conjunctivitis is the most common.[1] Others include:
Usually nonurgent

  • blepharitis[5] – a usually chronic inflammation of the eyelids with scaling, sometimes resolving spontaneously
  • subconjunctival hemorrhage[1] – a sometimes dramatic, but usually harmless, bleeding underneath the conjunctiva most often from spontaneous rupture of the small, fragile blood vessels, commonly from a cough or sneeze
  • inflamed pterygium[6] – a benign, triangular, horizontal growth of the conjunctiva, arising from the inner side, at the level of contact of the upper and lower eyelids, associated with exposure to sunlight, low humidity and dust. It may be more common in occupations such as farming and welding.
  • inflamed pinguecula[7] – a yellow-white deposit close to the junction between the cornea and sclera, on the conjunctiva. It is most prevalent in tropical climates with much UV exposure. Although harmless, it can occasionally become inflamed.
  • dry eye syndrome – caused by either decreased tear production or increased tear film evaporation which may lead to irritation and redness [8]
    acute glaucoma, angle closure type
  • airborne contaminants or irritants
  • tiredness
  • drug use including cannabis[9]
  • episcleritis[10] – most often a mild, inflammatory disorder of the 'white' of the eye unassociated with eye complications in contrast to scleritis, and responding to topical medications such as anti-inflammatory drops.

Usually urgent

  • acute angle closure glaucoma[11] – implies injury to the optic nerve with the potential for irreversible vision loss which may be permanent unless treated quickly, as a result of increased pressure within the eyeball. Not all forms of glaucoma are acute, and not all are associated with increased 'intra-ocular' pressure.
  • injury
  • keratitis[11] – a potentially serious inflammation or injury to the cornea (window), often associated with significant pain, light intolerance, and deterioration in vision. Numerous causes include virus infection. Injury from contact lenses can lead to keratitis.
eye with iritis showing ciliary flush
  • iritis[1] – together with the ciliary body and choroid, the iris makes up the uvea, part of the middle, pigmented, structures of the eye. Inflammation of this layer (uveitis) requires urgent control and is estimated to be responsible for 10% of blindness in the United States.
  • scleritis[12] – a serious inflammatory condition, often painful, that can result in permanent vision loss, and without an identifiable cause in half of those presenting with it. About 30–40% have an underlying systemic autoimmune condition.
  • tick-borne illnesses like Rocky Mountain spotted fever[13] – the eye is not primarily involved, but the presence of conjunctivitis, along with fever and rash, may help with the diagnosis in appropriate circumstances.

See also


  1. Cronau, H; Kankanala, RR; Mauger, T (Jan 15, 2010). "Diagnosis and management of red eye in primary care". American Family Physician. 81 (2): 137–44. PMID 20082509.
  2. Narayana, S; McGee, S (November 2015). "Bedside Diagnosis of the 'Red Eye': A Systematic Review". The American Journal of Medicine. 128 (11): 1220–1224.e1. doi:10.1016/j.amjmed.2015.06.026. PMID 26169885.
  3. Leibowitz HM (2000). "The red eye". N Engl J Med. 343 (5): 345–51. doi:10.1056/nejm200008033430507. PMID 10922425.
  4. Rezende RA, Uchoa UB, Uchoa R, Rapuano CJ, Laibson PR, Cohen EJ (2004). "Congenital corneal opacities in a cornea referral practice". Cornea. 23 (6): 565–70. doi:10.1097/01.ico.0000126317.90271.d8. PMID 15256994.
  5. Jackson WB (April 2008). "Blepharitis: current strategies for diagnosis and management". Can J Ophthalmol. 43 (2): 170–79. doi:10.3129/i08-016. PMID 18347619.
  6. Bradley JC, Yang W, Bradley RH, Reid TW, Schwab IR (July 2010). "The science of pterygia". Br J Ophthalmol. 94 (7): 815–20. doi:10.1136/bjo.2008.151852. PMID 19515643.
  7. Sutphin, John, ed. 2007–2008 Basic and Clinical Science Course Section 8: External Disease and Cornea. American Academy Ophthalmology. p. 365. ISBN 1-56055-814-8.
  8. "Keratoconjunctivitis, Sicca". eMedicine. WebMD, Inc. January 27, 2010. Retrieved September 3, 2010.
  9. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR). Washington DC: American Psychiatric Association; 2000.
  10. Jabs DA, Mudun A, Dunn JP, Marsh MJ (October 2000). "Episcleritis and scleritis: clinical features and treatment results". Am J Ophthalmol. 130 (4): 469–76. doi:10.1016/S0002-9394(00)00710-8. PMID 11024419.
  11. Dargin JM, Lowenstein RA (February 2008). "The painful eye". Emerg Med Clin North Am. 26 (1): 199–216. doi:10.1016/j.emc.2007.10.001. PMID 18249263.
  12. Sims, J (December 2012). "Scleritis: presentations, disease associations and management". Postgrad Med J. 88 (1046): 713–18. doi:10.1136/postgradmedj-2011-130282. PMID 22977282.
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