Q. What Causes Conjunctivitis? I woke up this morning with a red eye. My doctor said it's probably conjunctivitis. What causes this? A. Red eye as a result of conjunctivitis is caused by hyperemia of the superficial blood vessels of the conjunctiva in the eye. This is usually caused due to either an allergic reaction, infection or some other trigger such as a foreign body that penetrated the eye. The blood vessels in the eye become engorged and therefore seen as red on the white sclera. This requires immediate medical examination in order to rule out emergency situations that can lead to permanent damage.
Epidemic keratoconjunctivitis (EKC) is a highly contagious infection of the front part of the eye. The miserable infection can be easily spread by coming into contact with the tears or discharge from the eyes of an infected person. A person could catch the infection by touching a contaminated surfaces or object and hen touching their own eyes. Symptoms can be quite bothersome, including redness, itching, irritation and tearing but usually resolve in about two weeks. If you develop EKC, it is important to practice good hygiene (frequent hand washing) to avoid spreading the infection to other people.
There are more serious conditions that can present with a red eye such as infectious keratitis, angle-closure glaucoma, or iritis. These conditions require the urgent attention of an ophthalmologist. Signs of such conditions include decreased vision, significantly increased sensitivity to light, inability to keep eye open, a pupil that does not respond to light, or a severe headache with nausea.  Fluctuating blurring is common, due to tearing and mucoid discharge. Mild photophobia is common. However, if any of these symptoms are prominent, it is important to consider other diseases such as glaucoma , uveitis , keratitis and even meningitis or carotico-cavernous fistula .