Bacterial, Chlamydial, and Mycobacterial Infections

Abstract

The ocular surface is a complex biological structure responsible for the maintenance of corneal clarity, as well as protection of the eye against microbial and mechanical insults. In addition to serving as a physical barrier to the external environment, it has an important role in innate and adaptive immunity. The commensal flora that exist on the ocular surface have a protective role in preventing the proliferation of pathogenic species, and any alteration that disturbs the homeostatic microbiome may lead to ocular pathologies. For the purpose of this review, the ocular surface will be defined as consisting of the conjunctiva, cornea, and tear film. The ocular surface has both specific and nonspecific defense mechanisms to prevent microbial and viral infections. Worldwide, bacteria are the major contributor of ocular infections. They are associated with many types of ocular infections and with many factors including contact lenses, trauma, surgery, and age. If left untreated, they can lead to visual impairment and blindness. Diseases that affect the conjunctiva and cornea will be discussed with a focus on bacterial conjunctivitis and keratitis. Bacterial conjunctivitis, inflammation of the mucosa of conjunctiva, is commonly seen in children but is present among neonates and adults. In neonates, the most common cause of conjunctivitis is infection by Chlamydia trachomatis. After cataracts, bacterial keratitis, inflammation of the cornea, is the second-largest cause of legal blindness worldwide. Corneal injury, surgery trauma, dry eyes, and contact lens wear are the most common predisposing factors for keratitis. The most common pathogenic bacteria associated with bacterial keratitis are Staphylococcus aureus and, for contact lens wearers, Pseudomonas aeruginosa. With the increasing use of LASIK, nontuberculous mycobacterial keratitis, while rare, maybe increasing in frequency. Infectious keratitis can progress rapidly and generally requires urgent therapy to eliminate the pathogen.