Endophthalmitis

Etiologic Agents

A wide variety of microorganisms can cause endophthalmitis. Gram-positive cocci (both staphylococci and streptococci) are leading pathogens for both exogenous and endogenous endophthalmitis. In recent years, gram-positive isolates have become increasingly resistant to antibiotics, including early generation fluoroquinolones, but resistance to vancomycin and fourth-generation fluoroquinolones remains uncommon. Staphylococcus epidermidis is the organism most often identified in the postoperative setting and is a frequent agent of posttraumatic endophthalmitis as well. Often, S. epidermidis infection has a subacute onset 1 week to 1 month after surgery. Neonatal group B streptococcal septicemia can be associated with endogenous endophthalmitis.

The gram-positive anaerobic bacillus Propionibacterium acnes is one of the most common causes of endophthalmitis after cataract surgery. Characteristically, P. acnes endophthalmitis develops one to several months after surgery and follows a chronic smoldering course. In contrast, Bacillus cereus is the most virulent organism inside the eye, capable of destroying the entire retina within hours of introduction by trauma or hematogenous seeding.

Neisseria meningitidis was the most common cause of endogenous endophthalmitis before the advent of antibiotics and still must be recognized as having a predilection for intraocular localization. Nontypable Haemophilus influenzae can cause endophthalmitis after accidental trauma and surgery. During the past decade, Klebsiella pneumoniae has emerged as the predominant cause of endogenous endophthalmitis in East Asia. Numerous other gram-negative bacilli (notably Pseudomonas aeruginosa and Escherichia coli ) have been associated with both exogenous and endogenous endophthalmitis, especially after trauma or surgery and in individuals with underlying conditions

Candida albicans bloodstream infection (BSI) remains the most common fungal precursor of endogenous endophthalmitis, although this complication appears to be decreasing in frequency with earlier initiation of systemic treatment for candidemia and invasive candidiasis. Meta-analysis of neonatal Candida BSI showed 3% prevalence of endophthalmitis. Non- albicans Candida spp. and a variety of other fungi (including Aspergillus and Fusarium, Alternaría , and Scedosporium spp.) have been implicated in both endogenous and exogenous endophthalmitis, especially in posttraumatic cases or immunocompromised hosts. Fungal endophthalmitis tends to follow a more indolent course than that of most bacterial infections.

Epidemiology and Host Factors

Postoperative endophthalmitis most often follows cataract extraction but can be associated with any form of intraocular procedure or extraocular operations, such as strabismus repair (in which organisms presumably are introduced into the globe by inadvertent needle perforation of the sclera). The rate of endophthalmitis after pediatric intraocular surgery is similar to that found in adults, approximately 1 in 1000 cases. A recent trend in cataract surgery toward use of unsutured “self-sealing” incisions through temporal clear cornea (as opposed to the superior limbus) has been associated with a small but substantial increase in the frequency of postoperative endophthalmitis.

Filtering operations for glaucoma (which produce a fistulous connection for aqueous flow through the corneoscleral limbus between the anterior chamber and a conjunctival bleb) lower the physical resistance of the globe to invasion by microorganisms, creating a higher risk for intraocular infections. These infections can persist for decades if the drainage tract remains patent. The frequency of late bleb-related endophthalmitis appears to have increased considerably in children as well as in adults because of increasing use of periocular antifibrotic agents (mitomycin C or 5-fluorouracil) administered intraoperatively or postoperatively. These drugs improve the rate of successful lowering of intraocular pressure after filtering surgery but tend to result in blebs that are large and thin-walled and, thus, particularly vulnerable to bacterial invasion.

An inflammatory condition that occurs after intraocular surgery, toxic anterior segment syndrome, can be confused with postoperative infectious endophthalmitis. In this condition, toxins on surgical instruments that have been improperly sterilized lead to an inflammatory reaction within days after the anterior segment surgery. Because the consequence of delayed treatment of an infectious process can be devastating, intraocular empiric antibiotics should be initiated after specimens of aqueous and vitreous samples have been obtained for culture but before the diagnosis has been confirmed.

Endophthalmitis is a major concern after any penetrating trauma to the globe, especially in childhood, when contamination of the causative instrument with soil, saliva, or fecal material is common. Occult penetration of the globe by a needle, thorn, or similarly shaped object can be unsuspected in a nonverbal child until days later when infection leads to obvious inflammatory signs. In a child with posttraumatic endophthalmitis, the possibility of an intraocular foreign body (which needs to be removed surgically) must be considered and should be excluded, if necessary, with ultrasonographic or radiographic imaging.

Endogenous endophthalmitis usually occurs in a host who is already known to have BSI or is immunocompromised, but occasionally, ocular involvement is the first indication of the underlying problem. Endocarditis and meningitis are the most important localized infections associated with endophthalmitis. Patients with diabetes have the propensity for retinal spread of K. pneumoniae from hepatic abscesses and of E. coli from a urinary tract infection.

Most cases of endogenous candidal endophthalmitis are nosocomial, occurring in association with indwelling intravascular catheters, use of broad-spectrum antibiotics, or immunosuppressive or major surgical treatment. Infants with intraocular candidiasis or bacterial endophthalmitis usually have a history of premature birth and pulmonary disease.