Why do our eyes turn red?


Red eyes are a sign of inflammation that manifests itself through dilation and irritation of the blood vessels on the surface of the eye, with localised or diffuse hyperemia (redness) being observed on the anterior surface of the eye. It is one of the main reasons for consultation with eye care professionals, as well as in primary care, and the most frequent in ophthalmologic emergencies. There are numerous causes, and many of them are not serious, such as eye fatigue, excessive contact lens wear, dry eyes, the presence of a foreign body in the eye, or allergic conjunctivitis. However, in some cases, red eyes are the clinical sign of a more serious eye disease.

Depending on the type of redness or hyperemia, several clinical categories can be established:

  • Hyperemia of the most superficial blood vessels or conjunctival injection. It decreases as we approach the sclerocorneal limbus, is associated with a pathology in the eyelid and conjunctiva, and is usually not serious. 
  • Hyperemia of the deeper conjunctival vessels or ciliary injection. It is more pronounced at the level of the sclerocorneal limbus and is associated with more severe pathologies in the anterior segment, i.e., inflammation in the cornea, iris, or ciliary body.
  • Hyperemia of superficial and deep vessels or mixed injection, associated with acute glaucoma.
  • Hyposphagma. It is a sudden, asymptomatic haemorrhage caused by vascular rupture. Occasionally it can occur in cases of arterial hypertension, although it occurs more frequently after exertion, trauma, or sudden changes in temperature. It usually does not require treatment and is often reabsorbed within a few weeks.

Conjunctivitis and hyposphagma are often the most common causes of red eye and are considered relatively benign processes. However, if eye redness is associated with pain, blurred vision, eye secretions, abnormal intraocular pressure, or other alterations of the anterior segment, we may be facing a more serious process. Therefore, a correct case history and exploration of the anterior segment are important in order to identify eye pathologies requiring urgent ophthalmological evaluation.

Begoña Domenech Amigot is a professor of the Department of Optics, Pharmacology, and Anatomy of the University of Alacant

© Mètode 2018