Conjunctivitis overview

# Overview
Conjunctivitis (conjunctivitis) is an inflammation of the conjunctiva (the outermost layer of the eye and the inner surface of the eyelids), most commonly due to an allergic reaction or an infection (usually bacterial or viral). Conjunctivitis may be classified based on the duration of symptoms into hyperacute, acute, or chronic.
Additionally, based on the causality of the inflammation and age group, conjunctivitis may be classified into infective conjunctivitis (bacterial and viral), neonatal conjunctivitis (ophthalmia neonatorum), allergic conjunctivitis, keratoconjunctivitis sicca (dry eye syndrome), and superior limbic keratoconjunctivitis (SLK). 
Common causes of conjunctivitis include bacteria, viruses, and environmental factors.
Viral conjunctivitis is the most common cause of infectious conjunctivitis both overall and in the adult population. Between 65% and 90% of cases of viral conjunctivitis are caused by adenoviruses. Bacterial conjunctivitis is the second most common cause. 
Allergic conjunctivitis is the most frequent cause, affecting 15% to 40% of the population.
Noninfectious conjunctivitis includes keratoconjunctivitis sicca (dry eye syndrome) and superior limbic keratoconjunctivitis, which may caused by inflammation secondary to immune-mediated diseases.
Prognosis for conjunctivitis usually good with treatment. Infective conjunctivitis resolves, in 65% of cases, within 2-5 days.
Complete history will help determine the correct therapy.
The symptoms of conjunctivitis differ based on the cause of the inflammation. Common symptoms to all forms of conjunctivitis include redness, excessive tearing, and irritation. Photophobia, itching, mucopurulent or non-purulent discharge, chemosis, burning eyes, blurred vision, and eyelid swelling are variable.
Physical examination of patients with conjunctivitis is usually remarkable for conjunctival injections, epiphora, hyperemia, chemosis, and muco-purulent or watery discharge. However, ophthalmologic examination may be varies based on conjunctivitis subtypes.
Laboratory tests are not often required in patients with mild conjunctivitis. Conjunctival cultures are generally reserved for conjunctivitis presenting with severe purulent discharge, and cases suspicious for gonococcal or chlamydial infection. 
Allergic conjunctivitis may be treated with artificial tears and topical antihistamines, vasoconstrictive agents, mast cell stabilizers, NSAIDs, and corticosteroids. Cool compresses are recommended to reduce eyelid and periorbital edema. Topical antimicrobial therapy is only recommended for patients with either bacterial or herpetic conjunctivitis, but not allergic or adenoviral conjunctivitis. Systemic antibiotic therapy is necessary to treat conjunctivitis due to Neisseria gonorrhoeae and Chlamydia trachomatis.

# Historical Perspective
Conjunctivitis is an ancient disease. In 1750, neonatal conjunctivitis (ophthalmia neonatorum) was first described by S.T. Quellmaz.
In 1883, Koch discovered the bacilli of two different forms of infectious conjunctivitis, or Egyptian ophthalmia.

# Classification
Conjunctivitis may be classified based on the duration of symptoms into hyperacute, acute, and chronic.
Additionally, conjunctivitis may be classified according to the causality of the inflammation or age groups into several subtypes: infective conjunctivitis (bacterial and viral), neonatal conjunctivitis (ophthalmia neonatorum), allergic conjunctivitis, keratoconjunctivitis sicca (dry eye syndrome), superior limbic keratoconjunctivitis, and chemical conjunctivitis.

# Pathophysiology
Conjunctivitis is defined as inflammation of bulbar and/or palpebral conjunctiva. Conjunctivitis has many etiologies, but the majority of cases can be caused by allergies or infection. Infective conjunctivitis is an infection of the conjunctiva either caused by viruses or bacteria. Airborne antigens may be involved in the pathogenesis of allergic conjunctivitis. Common airborne antigens include pollen, grass, and weeds. Keratoconjunctivitis sicca (dry eye syndrome) is a multifactorial disease and associated with different medical conditions.

# Causes
Common causes of conjunctivitis include bacteria, viruses, and environmental factors.
Viral conjunctivitis is the most common cause of infectious conjunctivitis both overall and in the adult population. Bacterial conjunctivitis is the second most common cause and is responsible for the majority of cases in children(Haemophilus influenzae,Moraxella catarrhalis,Streptococcus pneumoniae). Most of the cases in adults are caused by Staphylococcus aureus. Allergic conjunctivitis is the most frequent cause, affecting 15% to 40% of the population.
Noninfectious conjunctivitis includes keratoconjunctivitis sicca (dry eye syndrome) and superior limbic keratoconjunctivitis caused by inflammation secondary to immune-mediated diseases or mechanical irritation.

# Differentiating Conjunctivitis from Other Diseases
Conjunctivitis symptoms and signs are relatively non-specific. Even after biomicroscopy, laboratory tests are often necessary to determine the underlying pathophysiology with certainty. An eye examination can help to differentiate conjunctivitis from other medical conditions. Conjunctivitis must be differentiated from blepharitis, keratitis, and scleritis.

# Epidemiology and Demographics
Conjunctivitis accounts for 1% of all primary care and emergency room visits.
The incidence of viral conjunctivitis is approximately 80,000 per 100,000 cases with acute conjunctivitis. Viral conjunctivitis more commonly affects adults while bacterial conjunctivitis more commonly affects children. The prevalence of conjunctivitis varies according to the underlying cause, which may be influenced by the patients age, as well as the season of the year.

# Risk Factors
The most potent risk factor in the development of infective conjunctivitis is a direct or indirect contact with an infected persons eye drainage.
Common risk factors in the development of conjunctivitis are poor hygienic habits, contaminated personal articles, history of ocular diseases (dry eye, blepharitis, and anatomic abnormalities of the ocular surface), recent ocular surgery, medication use, and history of autoimmune disorders. Additionally, vaginal delivery is a risk factor for conjunctivitis in babies born to mothers infected with either Neisseria gonorrhoeae or Chlamydia trachomatis.

# Screening
General screening for conjunctivitis is not recommended. However, according to the Centers for Disease Control and Prevention (CDC), screening for sexually transmitted diseases (STDs) is recommended among pregnant women to prevent conjunctivitis and other medical conditions in newborns.

# Natural History, Complications, and Prognosis
If left untreated, viral conjunctivitis will generally clear without any complications. Bacterial conjunctivitis is often self-limited. If left untreated, bacterial conjunctivitis will clear within 1 or 2 weeks without any complications, and it is generally associated with a favorable long-term prognosis. Allergic conjunctivitis improves by eliminating or significantly reducing contact with the allergen. If left untreated, most cases of allergic conjunctivitis may resolve without any long-term consequences. Keratoconjunctivitis sicca associated with Sjogren's syndrome is associated with a particularly poor prognosis and requiring a longer course of treatment. Prognosis for conjunctivitis is generally good with treatment.

# Diagnosis

## History and Symptoms
The symptoms of conjunctivitis differ based on the cause of the inflammation. Redness, excessive tearing, and irritation are symptoms common to all forms of conjunctivitis. Photophobia, itching, mucopurulent or non-purulent discharge, chemosis, burning eyes, blurred vision and eyelid swelling are variable. Complete history will help to determine whether the condition is associated with any specific environmental or work-related exposure.

## Physical Examination
Physical examination of patients with conjunctivitis is usually remarkable for conjunctival injections, epiphora, hyperemia, chemosis, and muco-purulent or watery discharge. However, ophthalmologic examination may be varies based on conjunctivitis subtypes.

## Laboratory Findings
Laboratory tests are not often required in patients with mild conjunctivitis. Conjunctival cultures are generally reserved for recurrent conjunctivitis, conjunctivitis recalcitrant to therapy, conjunctivitis presenting with severe mucopurulent discharge, and cases suspicious for gonococcal or chlamydial infection.

## Imaging Findings
There are no imaging findings associated with conjunctivitis. However, dynamic meibomian imaging (DMI) can be used to obtain a distinct picture of the entire everted inferior tarsal plate in a patient with keratoconjunctivitis sicca (dry eye syndrome).

## Other Diagnostic Studies
Other diagnostic studies for viral conjunctivitis include rapid antigen testing.
Other diagnostic studies for keratoconjunctivitis sicca (dry eye syndrome) conjunctivitis include corneal sensation, tear break up time, ocular surface staining, and Schirmer's test.

# Treatment

## Medical Therapy
Allergic conjunctivitis may be treated with artificial tears and topical antihistamines, vasoconstrictive agents, mast cell stabilizers, NSAIDs, and corticosteroids. Cool compresses are recommended to reduce eyelid and periorbital edema. Topical antimicrobial therapy is only recommended for patients with either bacterial or herpetic conjunctivitis, but not allergic or adenoviral conjunctivitis. Systemic antibiotic therapy is necessary to treat conjunctivitis due to Neisseria gonorrhoeae and Chlamydia trachomatis.

## Surgery
Surgical intervention is not recommended for the management of infective and neonatal conjunctivitis. Allergic conjunctivitis is a self-limited disease, and extensive surgery may not be acceptable. However, surgical techniques include superficial keratectomy and penetrating keratoplasty are usually reserved for severe cases of corneal involvement. Despite the availability of efficient tear substitutes, many patients with keratoconjunctivitis sicca (dry eye syndrome) experience severe corneal injuries and a subsequent loss of vision. Surgical techniques include lateral tarsorrhaphy, punctal plugs, lens therapy, amniotic membrane transplantation, and salivary gland duct transposition.

## Primary Prevention
There are no formal established methods for primary prevention of allergic conjunctivitis, keratoconjunctivitis sicca (dry eye syndrome), and superior limbic keratoconjunctivitis. However, early determination of these conditions is very important in terms of morbidity.

## Secondary Prevention
Secondary prevention strategies following conjunctivitis include discontinued contact lens wear (infective conjunctivitis), ocular prophylaxis with 0.5% erythromycin ointment or 1% tetracycline hydrochloride (ophthalmia neonatorum), and avoiding the offending antigen (allergic conjunctivitis). 
Secondary prevention strategies following keratoconjunctivitis sicca (dry eye syndrome) include avoiding very dry environments, dusty areas, and prolonged visual tasks. There is no established method for secondary prevention of superior limbic keratoconjunctivitis (SLK). However, educating patients about disease process can improve compliance of patients with treatment, and help them to cope with the often prolonged symptoms.