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Chapter: 11th Microbiology : Chapter 12 : Medical Microbiology

Ocular Infections

A number of microorganisms cause infection when introduced into the mucosa of the eye.

Ocular Infections

A number of microorganisms cause infection when introduced into the mucosa of the eye. In general, bacterial eye infections can lead to inflammation, irritation, and discharge, but they vary in severity. Some are typically short-lived, and others are chronic and lead to permanent eye damage. Prevention requires limiting the exposure to contagious pathogens. When infections do occur, prompt treatment with antibiotics can often limit or prevent permanent damage.

The external surfaces of the eye viz. the conjunctiva and cornea are susceptible to infection. These are exposed to external world and are easily accessible to infective agents. Particularly the conjunctiva is susceptible because it is covered with eyelid that provides warm, moist and enclosed environment in which contaminating organisms can quickly establish a focus of infection. However, eyelid and tears protect the external surfaces of the eye, both mechanically and biologically (Figure 12.13).


Factors that Protect the External Surfaces of the Eye

1. Eyelid gives mechanical protection to the surfaces 2. Tears (a) make the surfaces moist and prevent drying. (b) contains lysozyme- an enzyme that lyses the cell wall of Gram positive bacteria. (c) contains IgA antibodies that provide first line defense against viruses.


Infection of Eyelid

Most common cause of eyelid infection is Staphylococcus aureus.

Infection involves lid margins and cause blepharitis.

When the eyelid glands or follicles are affected stye (sticky eye) is seen (Figure 12.14).

Conjunctivitis (inflammation of conjunctiva) Conjunctivitis or pink eye can be caused by many different kinds of viruses and bacteria.



Trachoma, or granular conjunctivitis, is a common cause of preventable blindness that is rare in the United States but widespread in developing countries, especially in Africa and Asia. The condition is caused by the same species that causes neonatal inclusion conjunctivitis in infants, Chlamydia trachomatis. Chlamydia trachomatis can be transmitted easily through fomites such as contaminated towels, bed linens, and clothing and also by direct contact with infected individuals. Chlamydia trachomatis can also spread by flies that transfer infected mucous containing Chlamydia trachomatis from one human to another. Infections of eye are listed in Table 12.6.

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