The herb eyebright has been used since the Middle Ages as an eyewash for infection or inflammation of the eye. However, as much as one would like to believe that all traditions are wise, eyebright appears to have been selected for treating eye diseases not because it works particularly well, but because its petals look bloodshot.1 This follows from the classic medieval philosophic attitude known as the Doctrine of Signatures, which states that herbs show their proper use by their appearance.
Like many herbs, eyebright contains astringent substances and volatile oils that are probably at least slightly antibacterial. But there's no evidence that eyebright is particularly effective for treating conjunctivitis (pink eye) or any other eye disease; Germany's Commission E recommends against using it. Warm compresses consisting of nothing but water (or ordinary black tea) are probably equally effective under the same conditions.
Eyebright tea is also sometimes taken internally to treat jaundice, respiratory infections, and memory loss. However, there is no evidence that it is effective for any of these conditions.
Traditionally, eyebright tea is made by boiling 1 tablespoon of the herb in a cup of water. This is then used as an eyewash or taken internally up to 3 times daily.
Eyebright can cause tearing of the eyes, itching, redness, and many other symptoms, probably due to direct irritation.2 It appears to be safe when taken internally, but not many studies have been performed. Safety in young children, pregnant or nursing women, or those with severe liver or kidney disease has not been established.