FOLLICULAR CONJUNCTIVAL REACTION :Conjunctivitis is conjunctival vascular dilation (hyperemia), sometimes accompanied by conjunctival edema and discharge. The presence of a follicular conjunctival response, as distinct from a papillary conjunctival response, is helpful in differentiating between the two. Follicles constitute lymphoid germinal centers. They appear as smooth, rounded nodules beneath the conjunctival epithelium. These nodules are avascular at their apices and are surrounded by fine vessels at their bases. When follicular conjunctivitis is present, regional lymphadenopathy often coexists, representing a similar lymphoblastic proliferation. The main causes of follicular conjunctivitis include adenoviral infection, primary herpes simplex viral infection, molluscum contagiosum infection, enteroviral infection, chlamydial infection, and toxicity from certain medications. 

PAPILLARY CONJUNCTIVAL REACTION: In contrast to a follicular conjunctival response, a papillary conjunctival response is nonspecific and can be caused by many agents. It can occur in any nonspecific conjunctival inflammation, including mechanical irritation and allergic eye disease. It is usually seen on the upper tarsal conjunctiva, a papillary response is a fine mosaic pattern of dilated, telangiectatic blood vessels. Papillae vary in size from tiny red dots to polygonal elevations. Each papilla has a central fibrovascular core that gives rise to a vessel branching outward in a spoke like pattern. The connective tissue septa surrounding the papillae are anchored in the conjunctival stroma, resulting in hyperemic areas surrounded by pale tissue when papillary hypertrophy occurs.

Adenoviral conjunctivitis: Most forms of viral conjunctivitis begin with a hyperemic and congestive conjunctival reaction, and within days stimulate a follicular and papillary conjunctivitis. In adenoviral conjunctivitis, the onset is usually abrupt; in the vast majority of cases it involves the fellow eye within days. Conjunctival follicles develop, accompanied by serous discharge and preauricular lymphadenopathy. More severe conjunctival inflammation can lead to the formation of fibrinous pseudomembranes or membranes and sometimes to conjunctival scarring. Punctate epithelial keratitis can be associated with significant irritation and photophobia and usually progresses to immune-mediated subepithelial infiltrates (epidemic keratoconjunctivitis; see page 4).Conjunctival inflammation gradually resolves over a few weeks, but the corneal manifestations may be prolonged.