The gritty and/or scratchy feeling is sometimes localized enough for patients to insist they must have a foreign body in the eye. Bacteria such as Chlamydia trachomatis or Moraxella can cause a non-exudative but persistent conjunctivitis without much redness.
Bacterial conjunctivitis may cause the production of membranes or pseudomembranes that cover the conjunctiva.
Classification can be either by cause or by extent of the inflamed area.
Blepharoconjunctivitis is the dual combination of conjunctivitis with blepharitis (inflammation of the eyelids).
Conjunctivitis may also be caused by allergens such as pollen, perfumes, cosmetics, smoke, Conjunctivitis is part of the triad of reactive arthritis, which is thought to be caused by autoimmune cross-reactivity following certain bacterial infections.
Cultures are not often taken or needed as most cases resolve either with time or typical antibiotics.
Swabs for bacterial culture are necessary if the history and signs suggest bacterial conjunctivitis but there is no response to topical antibiotics.
Viral conjunctivitis is often associated with an infection of the upper respiratory tract, a common cold, or a sore throat.
Its symptoms include excessive watering and itching.