Contributor: Gordon K. Klintworth
 Persons who are profoundly neutropenic or who have diabetes mellitus, disorders of the heart, and gastrointestine [infection - gastrointestinal] are prone to endophthalmitis. Penetrating ocular injuries, including surgical procedures can lead to endophthalmitis. Numerous organisms can cause endophthalmitis. Some reach the cornea via the blood stream (endogenous endophthalmitis); others enter it from local sources and injuries (exogenous endophthalmitis). Causes of endogenous endophthalmitis include bacteria [bacterial infection], which cause bacterial endophthalmitis [endophthalmitis - bacterial], fungi (Aspergillus). Endophthalmitis needs to be distinguished from panophthalmitis. Endophthalmitis may be preceded by an infection of the conjunctiva [conjunctivitis - bacterial] or cornea [keratitis - bacterial]. Bacterial endophthalmitis [endophthalmitis - bacterial] may follow bacterial keratitis. Endophthalmitis can occur in persons predisosed to bacterial infection

Trauma to the surface of the eye results in focal devitalization of epithelial cells and cell loss. Often the injury is minor and goes unnoticed or has been forgotten by the time a secondary complication develops. Contact lens wear is associated with an increased risk of infectious keratitis. Although the overall incidence of ulcerative keratitis occurring in contact lens patients is low, numerous cases with complications occur because of the large number of persons using contact lenses. Infections tend to be more common in patients who use soft lenses (both day-wear and exended-wear) than hard or gas permeable lenses. Infectious ulcers associated with disposable lenses have also been reported. Pseudomonas is one of the most common bacteria causing ulcerative keratitis in persons wearing contact lenses.
Marginal keratitis is common in persons with functionally abnormal leukocytes.
The use of topical corticosteroids on the eye dramatically dampens the effects of neutrophil-mediated inflammation. The lack of inflammatory response to invading bacteria in pseudocrystalline keratopathy is the result of topical corticosteroids. Bacteria proliferate relatively unimpeded between collagen lamellae in the virtual absence of inflammation. Infectious pseudocrystalline keratopathy is frequently caused by the growth of minimally virulent bacteria, such as S. viridans, and usually occurs in eyes having had previous accidental or surgical trauma.
Some fungi affecting the eye and orbital tissue have characteristic geographic distributions based on the environmental living conditions of the pathogen. Aspergillosis, which may involve the orbit, for example, occurs more commonly in areas with a hot, humid climate. Coccidioides immitis is endemic in the Southwestern region of the United States, in Northwestern and Central Mexico, Venezuela, and in the Gran Chaco Plain of South America. Blastomyces dermatitidis (Ajellomyces dermatitidis), the causative agent of North American blastomycosis, is found most frequently in the Southeastern United States, but also occurs in other areas of the United States, Canada, and Africa. Histoplasma capsulatum (Emmonsiella capsulata) is endemic to the Ohio and Mississippi River valleys and the Appalachian Mountains in the United States causes a characteristic ocular syndrome (ocular histoplasmosis syndrome) in regions where it is endemic. Histoplasma duboisii is found in Nigeria.
A warm, moist climate and a rural agricultural environment may influence the sensitivity of healthy eyes to fungi and fungal infections. Fungal keratitis is infrequent in northern latitudes. In the United States, Aspergillus, Candida, Cephalosporium and Fusarium are the most frequently isolated genera. Many fungi are ubiquitous in air, soil, and organic waste. Fusarium sp. is the predominant cause of fungal keratitis in the southern United States.The airborne fungi belonging to the Zygomycetes, settle in the paranasal sinuses and readily enter the orbital tissues causing severe disease in susceptible hosts such as poorly controlled diabetics. The conjunctiva, eyelid or intraocular tissues may become locally infected by Sporothrix schenckii, a saprophyte found on plants, green vegetables, and grass. Ocular sporotrichosis has generally been a localized infection and this fungus rarely causes systemic disease after entering the body at a site of injury. Crytococcosis that may be aquired from pigeon droppings and unpasterized cow's milk can affect the eye.