Reactive arthritis is highly associated with HLA-B27.Conjunctivitis is associated with the autoimmune disease relapsing polychondritis.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.
Swabs for bacterial culture are necessary if the history and signs suggest bacterial conjunctivitis but there is no response to topical antibiotics.
If this is combined with rhinitis, the condition is termed "allergic rhinoconjunctivitis".
The symptoms are due to release of histamine and other active substances by mast cells, which stimulate dilation of blood vessels, irritate nerve endings, and increase secretion of tears.
Adenoviruses is the most common cause of viral conjunctivitis (adenoviral keratoconjunctivitis).
Herpetic keratoconjunctivitis (caused by herpes simplex viruses) can be serious and requires treatment with acyclovir.