DEFINITIONS AND EPIDEMIOLOGY
Conjunctivitis, commonly referred to as “red eye” or “pink eye,” is a nonspecific term used to describe an inflammation of the conjunctiva, which can be caused by a wide range of conditions. The conjunctivas are the mucous membranes extending from the eyelid margin to the corneal limbus (corneal margin), forming the posterior layer of the eyelids and the anterior layer of the globe. Conjunctivitis may result from primary involvement of the conjunctival tissue or may occur as a secondary manifestation of other ocular or systemic conditions that produce conjunctival inflammation.
Conjunctivitis is prevalent worldwide. It is the most common ocular infection in childhood, usually affecting children younger than 6 years old with a peak incidence between 12 and 36 months.1 Infectious causes of conjunctivitis may be sporadic or related to outbreaks. In most cases, conjunctivitis is benign and self-limited.
The conjunctiva is a loose connective tissue that covers the surface of the eye (bulbar conjunctiva) and forms the inner layer of the eyelids (palpebral conjunctiva). This translucent mucous membrane is composed of highly vascular, nonkeratinized stratified squamous epithelium. It is adherent to the underlying sclera at the limbus. It also contains numerous goblet cells, which secrete the mucinous and aqueous layers of the tear film. Conjunctivitis is characterized by dilatation of the superficial conjunctival blood vessels resulting in hyperemia (injection) and edema of the conjunctiva, with discharge. In contrast, subconjunctival hemorrhage is a collection of extravasated blood. Fluid may accumulate beneath the loosely attached bulbar conjunctiva, causing it to swell away from the globe, making eye closure difficult, a phenomenon known as chemosis (Figure 24-1).
This patient is suffering from chemosis associated with allergic conjunctivitis. [Reproduced with permission from Knoop KJ, Stack LB, Storrow AB, et al. The Atlas of Emergency Medicine. 4th ed. New York, NY: McGraw-Hill Professional; 2016. Photo contributor: Timothy D. McGuirk, DO.]
The diversity of etiologies for conjunctivitis makes a detailed patient history the most important step in the differential diagnosis of conjunctivitis. The patient history should include the chief complaint such as itching, burning, tearing, discharge, pain, foreign body sensation, and photophobia. It also should include questions about the onset and course of the disease, whether it is acute or chronic, and whether it is progressive or stationary. The ocular history should include questions about previous episodes, prior exposure to infected individuals, history of trauma or contact lens wear, and the use of topical legend (i.e., prescription) or over-the-counter (OTC) medications or cosmetics. The general health history should include descriptions of recent upper respiratory tract infections, autoimmune disorders, atopy, skin conditions, and sexually transmitted infections. Finally, the social history such as environmental exposure and the family history of ocular diseases ...