Bacterial endophthalmitis
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Mehrsefat, M.D. [2]
Overview
Bacterial endophthalmitis means bacterial infection inside the eye, involving the vitreous and/or aqueous humors. Most cases of endophthalmitis are exogenous, and organisms are introduced into the eye via trauma, surgery, or an infected cornea. Endogenous endophthalmitis occurs when the eye is seeded via the bloodstream. Patients usually have symptoms from their underlying systemic infection, but sometimes present only with eye symptom
Historical Perspective
Classification
Based on how Infectious agents generally gain access to the posterior segment of the eye, bacterial endophthalmitis may be classified into:
- Exogenous bacterial endophthalmitis
- Postoperative bacterial endophthalmitis (consequence of intraocular surgery)
- Delayed postoperative bacterial endophthalmitis
- Posttraumatic bacterial endophthalmitis (following a penetrating injury of the globe)
- Endogenous bacterial endophthalmitis (hematogenous spread of bacteria to the eye from a distant anatomical site)
Pathophysiology
Exogenous bacterial endophthalmitis
Postoperative endophthalmitis has been reported following nearly every type of ocular surgery, such as cataract, glaucoma, retinal, radial keratotomy, and intravitreal injections. Following surgical procedure, the eye globe integrity disturbed. As a result ocular surface bacteria, most commonly coagulase-negative staphylococci, may contaminate the aqueous humor. Preoperative topical antimicrobial agents can decrease colony counts in the tear film, but they do not sterilize the area. The exact low rate of clinical infection following eye surgery (despite the relatively high prevalence of microorganisms in the eye) is not fully understood. It is thought that low rate of clinical infection following surgical procedure is explained by combination of low inoculum levels, low pathogenicity, and the innate ocular defenses against infection.
Postoperative bacterial endophthalmitis may also occur weeks to years following surgery. The exact pathogenesis of delayed postoperative bacterial endophthalmitis is not fully understood. It is thought that delayed postoperative bacterial endophthalmitis is caused by either sequestration of low-virulence organisms introduced at the time of surgery or delayed inoculation of organisms to the eye through wound abnormalities, suture tracks, or filtering blebs. Propionibacterium acnes is the most common microorganism encountered in delayed postoperative bacterial endophthalmitis. It may occur weeks to months after surgery.
Posttraumatic bacterial endophthalmitis occurs following penetrating ocular injuries. Following penetrating injury, the eye globe integrity disturbed. Penetrating ocular injuries are accompanied by infection at a much higher rate compere to postoperative endophthalmitis. The broad prevalence range is due to factors such as:
- Presence of an intraocular foreign body
- Delay primary globe repair
- Location and extent of laceration of the globe
Posttraumatic endophthalmitis associated with a greater variety of organisms. The most common isolated organisms include Gram-positive Staphylococcus epidermidis and Streptococcus species (as a part of the normal skin flora and regularly contaminate open wounds). Bacillus cereus is ranked second and some cases are polymicrobial.
Endogenous bacterial endophthalmitis
Endogenous bacterial endophthalmitis, is often seen in patients who are [[|bacteremia|bacteremic]] in situations such as endocarditis. Under normal circumstances, the blood-ocular barrier provides a natural resistance against invading organisms. Following bacteremia, the blood-borne organisms permeate the blood-ocular barrier by:
- Direct invasion (septic emboli)
- Change in vascular endothelium (caused by inflammatory mediators released during infection)
Causes
Postoperative Bacterial Endophthalmitis
Postoperative endophthalmitis has been reported following nearly every type of ocular surgery. Common causes of postoperative bacterial endophthalmitis include:
- Gram-positive bacteria (95%)
- coagulase-negative staphylococci (70%)
- Staphylococcus aureus (10%)
- Streptococci (9%)
- Enterococcus and mixed bacteria (5%)
- Gram-negative bacilli (6%)
Delayed Postoperative Bacterial Endophthalmitis
Common causes of delayed postoperative bacterial endophthalmitis include:
- Propionibacterium acnes (most common)
- Streptococcus species
Posttraumatic Bacterial Endophthalmitis
Common causes of posttraumatic bacterial endophthalmitis include:
- Streptococcus species
- Bacillus cereus
- Polymicrobial
Endogenous bacterial endophthalmitis
Common causes of endogenous bacterial endophthalmitis include:
- Gram-positive bacteria
- Staphylococcus aureus
- Bacillus cereus (primary bacterial cause in intravenous drug abusers and are most likely seeded from contaminated injection paraphernalia and drug solutions)
- Gram-negative organisms