Hyperemia of the conjunctiva from infection, allergy, or chemical reactions characterizes conjunctivitis. Bacterial and viral conjunctivitis are highly contagious but are also self-limiting after 2 weeks. Chronic conjunctivitis may result in degenerative changes to the eyelids. In the Western hemisphere, conjunctivitis is probably the most common eye disorder.
The most common causative organisms are the following:
bacterial: Staphylococcus aureus, Streptococcus pneumoniae, Neisseria gonorrhoeae, Neisseria meningitidis
chlamydial: Chlamydia trachomatis (inclusion conjunctivitis)
viral: adenovirus types 3, 7, and 8; herpes simplex virus type 1.
Other causes include allergic reactions to pollen, grass, topical medications, air pollutants, and smoke; occupational irritants (acids and alkalies); rickettsial diseases (Rocky Mountain spotted fever); parasitic diseases caused by Phthirus pubis and Schistosoma haematobium; and, rarely, fungal infections.
Vernal conjunctivitis (also called seasonal or warm-weather conjunctivitis) results from allergy to an unidentified allergen. This form of conjunctivitis is bilateral; it usually begins before puberty and persists for about 10 years. Sometimes it’s associated with other signs and symptoms of allergy commonly related to grass or pollen sensitivity.
An idiopathic form of conjunctivitis may be associated with certain systemic diseases, such as erythema multiforme, chronic follicular conjunctivitis (orphan’s conjunctivitis), thyroid disease, and Stevens-Johnson syndrome. Conjunctivitis may be secondary to pneumococcal dacryocystitis or canaliculitis from candidal infection.