What are the causes of conjunctivitis?

From the Guidelines

Conjunctivitis is primarily caused by viral infections, bacterial infections, allergies, and irritants, with the most common causes being adenoviruses, Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae, as well as allergic reactions to pollen, pet dander, or dust mites 1. The causes of conjunctivitis can be classified into several categories, including:

• Infectious conjunctivitis, which can be further divided into viral and bacterial conjunctivitis
• Noninfectious conjunctivitis, which includes allergic, mechanical/irritative/toxic, immune-mediated, and neoplastic types
• Conjunctivitis caused by systemic diseases, such as atopy or acute infections like gonorrhea Some specific types of conjunctivitis include:
• Allergic conjunctivitis, which results from exposure to allergens like pollen, pet dander, or dust mites
• Mechanical/irritative/toxic conjunctivitis, which occurs when irritants like chlorine, smoke, or air pollution contact the eye
• Contact lens-related keratoconjunctivitis, which can develop from improper lens hygiene or extended wear
• Giant papillary conjunctivitis (GPC), which is often associated with contact lens wear
• Medication-induced/preservative-induced keratoconjunctivitis, which can occur due to the use of certain eye drops or medications It is essential to differentiate between primary conjunctival disease and conditions in which conjunctival inflammation is secondary to systemic or ocular diseases, as treatment should be directed at correcting the underlying problems 1. Prevention of conjunctivitis is crucial, and individuals can protect themselves by using adequate eye protection, practicing proper hand hygiene, and avoiding touching their eyes 1. In addition, vaccination strategies, such as the chickenpox and shingles vaccines, can help reduce the incidence of varicella (herpes) zoster virus, which can cause conjunctivitis 1. Overall, conjunctivitis is a complex condition with various causes, and a thorough understanding of its etiology is necessary for effective diagnosis and treatment.

From the Research

Causes of Conjunctivitis

• Conjunctivitis can be caused by various factors, including:
  • Viral infections: Viral conjunctivitis is the most common overall cause of infectious conjunctivitis 2
  • Bacterial infections: Bacterial conjunctivitis is the second most common cause of infectious conjunctivitis, with most uncomplicated cases resolving in 1 to 2 weeks 2
  • Allergic reactions: Allergic conjunctivitis is encountered in up to 40% of the population, but only a small proportion of these individuals seek medical help 2
  • Sexually transmitted diseases: Conjunctivitis secondary to sexually transmitted diseases such as chlamydia and gonorrhea requires systemic treatment in addition to topical antibiotic therapy 2
  • Parasites: Microbial conjunctivitis may be caused by bacteria, viruses, or parasites 3

Bacterial Causes

• The most common bacterial causes of conjunctivitis include:
  • Staphylococcus aureus
  • Haemophilus influenzae
  • Streptococcus pneumoniae
  • Staphylococcus epidermidis
  • Moraxella species 4
  • Dolosigranulum pigrum: an emerging ocular pathogen 5

Risk Factors

• Certain factors can increase the risk of developing conjunctivitis, including:
  • Contact lens wear: Conjunctivitis caused by gonorrhea or chlamydia and conjunctivitis in contact lens wearers should be treated with antibiotics 2
  • Poor hygiene: Bacterial conjunctivitis is a contagious infection of the surface of the eye usually treated empirically with topical antibiotics 5