The conjunctiva is a thin semitransparent membrane that covers the white part of the eye called the sclera. The conjunctiva starts at the limbus of the cornea and covers both the sclera and posterior surface of the eyelids. The portion covering the scleral is referred to as the bulbar conjunctiva, and the portion on the posterior surface of the lids is the palpebral conjunctiva. Conjunctivitis, also known as pink eye, is an inflammation of the conjunctival tissue due to infection or other irritants. The three most common causes of conjunctivitis are viral, allergic, and bacterial, with viral from the family of adenovirus the most common. Conjunctivitis causes the eye to appear red, the blood vessel dilated and is usually accompanied by increased tearing and/or mucoid discharge.
The most common cause of viral conjunctivitis is the adenovirus. The adenovirus is part of the Adenoviridae family that consists of nonenveloped, double-stranded DNA virus. Frequently associated infections caused by the adenovirus include upper respiratory tract infections, eye infections, and diarrhea in children. Children are most susceptible to viral infections, and adults tend to get more bacterial infections. Viral conjunctivitis can be obtained by direct contact with the virus, airborne transmission, and reservoir such as swimming pools. 
Conjunctivitis, whether bacterial or viral, is a common problem that affects millions of Americans each year. In the United States, it is estimated that 1% of visits of a primary care physicians are related to conjunctivitis. While viral conjunctivitis is the most common cause, bacterial conjunctivitis is the second most common cause and distinguishing the two can be a challenge for primary care physicians. Frequently antibiotics are prescribed without good indication which could present an unnecessary financial burden on the patient and increase drug-resistant bacteria. Employers and schools typically require those with conjunctivitis to remain out of their locations until the infection clears, potentially adding to the economic burden placed on those infected.
Regardless of the etiology, most cases of conjunctivitis can be categorized as either papillary or follicular. Neither classification is pathognomonic for a particular disease entity. Papillary conjunctivitis produces a cobblestone arrangement of flattened nodules with central vascular cores. It is most commonly associated with an allergic immune response or is a response to a foreign body. Independent of the etiology, the histologic appearance of papillary conjunctivitis is the same: closely packed, flat-topped projections, with numerous eosinophils, lymphocytes, plasma cells, and mast cells in the stroma surrounding a central vascular channel.
Follicular conjunctivitis is seen in a variety of conditions, including inflammation caused by pathogens such as viruses, bacteria, toxins, and topical medications. In contrast to papillae, follicles are small, dome-shaped nodules without a prominent central vessel. Histologically, a lymphoid follicle is situated in the subepithelial region and consists of a germinal center with immature, proliferating lymphocytes surrounded by a ring of mature lymphocytes and plasma cells. The follicles in follicular conjunctivitis are typically most prominent in the inferior palpebral and forniceal conjunctiva.
Patients with viral conjunctivitis present with foreign body sensation, red eyes, itching, light sensitivity, burning, and watery discharge. Whereas with bacterial conjunctivitis, patients present with all the above symptoms, but with mucopurulent discharge and mattering of the eyelids upon waking. Those presenting with viral conjunctivitis usually have a recent history of an upper respiratory tract infection or recent contact with a sick individual. Visual acuity is usually at or near their baseline vision. The cornea can have subepithelial infiltrates that can decrease the vision and cause light sensitivity. The conjunctiva is injected (red) and can also be edematous. In some cases, a membrane or pseudomembrane can be appreciated in the fornix. Follicles, small, dome-shaped nodules without a prominent central vessel, can be seen on the palpebral conjunctiva. Palpation of the preauricular lymph nodes may reveal a reactive lymph node that is tender to the touch and will help differentiate viral conjunctivitis versus bacterial.
Laboratory testing is typically not indicated unless the symptoms are not resolving and infection last longer than 4 weeks. Laboratory testing can be indicated in certain situations such as a suspected chlamydial infection in a newborn, an immune compromised patient, excessive amounts of discharge, or suspected gonorrhea co-infection. In the office, physicians can run tests to positively identify adenovirus with a specificity and sensitivity of 89% and 94%, respectively. However, ophthalmologists usually make the diagnosis clinically without additional testing.
Treatment for viral conjunctivitis is aimed at symptomatic relief and not to eradicate the self-limiting viral infection. Resolution of conjunctivitis can take up to 3 weeks. Treatment includes using artificial tears for lubrication four times a day or up to ten times a day with preservative free tears. Cool compresses with a wet washcloth to the periocular area may provide symptomatic relief. Preventing the spread of infection to the other eye or other people requires the patient to practice good hand hygiene with frequent washing, avoidance of sharing towels or linens, and avoiding touching their eyes. A person is thought to shed the virus while their eyes are red and tearing. If a membrane or pseudomembrane is present, it can be peeled at the slit lamp to improve patient comfort and prevent any scar formation from occurring. These membranes can either be peeled with a jeweler forceps or a cotton swab soaked with topical anesthetic. Topical steroids can help with the resolution of symptoms. However, they can also cause the shedding of the virus to last longer. Patients should be informed that they are highly contagious and should refrain from work or school until their symptoms resolve. While using steroids, they may still shed the virus without the visual symptoms that would indicate that they have an infection. Steroids should be reserved for patients with decreased vision due to their subepithelial infiltrates or severe conjunctival injection causing more the expected discomfort.
While the most common causes of conjunctivitis are viral or bacterial and due to allergic reactions, there are other causes of conjunctivitis that should be considered when treatment does not improve symptoms. Uveitis is a local autoimmune reaction that causes the eye to become inflamed and is commonly mistaken for conjunctivitis. Uveitis can be a local reaction that is idiopathic or a manifestation of a systemic autoimmune disease such as rheumatoid arthritis, lupus, or ankylosis spondylitis. Systemic autoimmune disease such Sjogren syndrome or Stevens-Johnson syndrome can also mimic conjunctivitis by presenting with conjunctival erythema and discharge.
A systemic workup should be initiated if any of these diseases are suspected. The most life or sight-threatening masqueraders of conjunctivitis include cavernous carotid fistula, orbital cellulitis, and orbital hemorrhage. In cavernous carotid fistulas, an abnormal communication between the arterial and venous circulation form causing vasodilation of the venous system. Subsequently, the fistula can cause rupture and hemorrhage, leading to irreversible damage to the eye and/or death. Due to venostasis, the ophthalmic vein dilates and causes congestion of the episcleral vessels mimicking conjunctivitis. Proptosis and a pulsatile globe can help differentiate between a fistula and conjunctivitis. Orbital cellulitis is an infection posterior to the septum and involves the orbital contents. Patients present with similar symptoms of conjunctivitis, but will also have pain with eye movements or even restricted eye movements. Lastly, an orbital hemorrhage is an ophthalmic emergency. The cause is mostly traumatic, but it is possible to have a spontaneous hemorrhage, especially in patients on anticoagulants, that present with proptosis, tight eyelids, and erythema of the conjunctiva.
Even though viral conjunctivitis is a benign condition, it is contagious can be easily transmitted to others. While long-term sequelae are rare, chronic viral conjunctivitis can lead to a poor quality of life. Most cases take 1-4 weeks to recover without treatment. The morbidity is rare but can include corneal ulceration and punctate keratitis. Patients need to be educated that the condition is harmless and will resolve spontaneously. Hand washing should be emphasized since the infection is highly contagious. Parents and teachers should be educated on the importance of isolation in school to prevent epidemics. All patients with viral conjunctivitis who wear contact lenses should be told to refrain from wearing them until the symptoms have subsided. Follow up with an ophthalmologist is recommended to ensure that no complications have occurred. (Level V)