Causes
Several studies show that acute conjunctivitis occurs with almost equal frequency between bacterial and viral causes Mucopurulent conjunctivitis is caused by bacterial organisms.

• Gram-positive for the following cocci: Staphylococcus epidermidis, Streptococcus pyogenes, and Streptococcus pneumoniae

• Gram-negative for the following cocci: Neisseria meningitidis and Moraxella lacunata

• Gram-negative for the following rods: genus Haemophilus and family Enterobacteriaceae Hyperpurulent conjunctivitis usually is caused by N gonorrhoea.

• N gonorrhoea, Chlamydia trachomatis, and bacteria (mainly Staphylococcus species and S pneumoniae) cause conjunctivitis of the newborn.

  • Approximately 90% of infants receiving Crede prophylaxis for gonorrheal ophthalmic (silver nitrate application) experience a mild transient conjunctival injection and tearing with variable purulence that typically resolves in 24-48 hours.

  
  

• Many types of viruses, most commonly adenovirus, cause viral conjunctivitis.

• Atopic conjunctivitis

  typically occurs in male teenagers who have a history of childhood atopic dermatitis. It resembles vernal conjunctivitis but is not seasonal.

• Vernal conjunctivitis is a bilateral

  recurrent hypersensitivity that occurs during the warm months of the year, particularly in hot climates.

• Giant papillary conjunctivitis predominantly is associated with contact lens wear.

• Toxic conjunctivitis occurs with airborne irritants or a direct splash of liquid or powder to the eye.

• Unusual causes may be considered in patients with atypical presentations, including parasitic (eg, Loa loa, Trichinella, Onchocera), autoimmune (sicca, pemphigoid), and systemic diseases (sarcoidosis, tuberculosis, Reiter syndrome, Kawasaki disease)