Conjunctival scrapes for cytology can be useful in detecting chlamydial and fungal infections, allergy, and dysplasia, but are rarely done because of the cost and the general lack of laboratory staff experienced in handling ocular specimens.
Conjunctival incisional biopsy is occasionally done when granulomatous diseases (e.g., sarcoidosis) or dysplasia are suspected.
Though very rare, hyperacute cases are usually caused by Neisseria gonorrhoeae or N. Chronic cases of bacterial conjunctivitis are those lasting longer than 3 weeks, and are typically caused by Staphylococcus aureus, Moraxella lacunata, or gram-negative enteric flora.
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.
Irritant or toxic conjunctivitis show primarily marked redness.
If due to splash injury, it is often present in only the lower conjunctival sac.
A patch test is used to identify the causative allergen in the case where conjunctivitis is caused by allergy.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.The infection usually begins with one eye, but may spread easily to the other.Viral conjunctivitis shows a fine, diffuse pinkness of the conjunctiva, which is easily mistaken for the ciliary infection of iris (iritis), but there are usually corroborative signs on microscopy, particularly numerous lymphoid follicles on the tarsal conjunctiva, and sometimes a punctate keratitis. Symptoms consist of redness (mainly due to vasodilation of the peripheral small blood vessels), swelling of the conjunctiva, itching, and increased lacrimation (production of tears).