Eyebright is a small, annual plant with deeply cut leaves, native to the heaths and pastures of Britain, the European continent, and subarctic regions of North America. Similar to several genera of the Scrophulariaceae, Euphrasia is hemiparasitic; the roots have foodgathering nodules that attach to the roots of surrounding plants in order to obtain food. Therefore, eyebright is difficult to cultivate, and virtually the entire supply is harvested from the wild, with little attention to species differences.
Eyebright stimulates the liver to remove toxins from the body. It has been used internally and externally to treat eye infections and afflictions, such as pink-eye. The herb strengthens the eye, and helps to repair damage. Eyebright tightens the mucous membranes of the eye and appears to relieve the inflammation of conjunctivitis and blepharitis. Its ability to counter mucus means that eyebright is often used for infectious and allergic conditions affecting the eyes, middle ear, sinuses, and nasal passages. Although eyebright counters liquid mucus, it should be used guardedly for dry and stuffy congestion, which tends to be made worse by the plant's astringency.
When it is taken by mouth, eyebright is used to treat respiratory conditions including allergies, bronchitis, colds, and sinusitis. Astringent chemicals known as tannins contained in eyebright may shrink and tighten the top layers of mucous membranes, thereby reducing mucus secretion, relieving irritation, and improving tissue firmness. As a result, eyebright is thought to help control symptoms such as watery eyes or runny nose associated with allergies. Eyebright also contains chemicals, especially caffeic acid, that may have antibacterial properties.
As its name implies, eyebright has also been taken by mouth or used as an eye wash for treating conditions of the eye. The tannins in it may decrease eye inflammation, as well as making a protective film over the surface of the eye. The caffeic acid may act as an anti-infective agent. Generally, however, any product for use in the eye should not be homemade. Eye drops and eye washes should be packaged commercially under sterile conditions.