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Pseudomonas aeruginosa is a gram-negative rod. It is an opportunistic human pathogen, known to cause a variety of infectious diseases. In the eye, P. aeruginosa is a common cause of bacterial keratitis, particularly in contact lens wearers. It is known to be particularly virulent, with pseudomonas keratitis being more difficult to treat and have worse prognosis than other forms of bacterial keratitis. P. aeruginosa secretes proteases that can cause liquefactive necrosis of the cornea, leading to rapid corneal weakening and perforation.
Pseudomonas is the leading cause of gram-negative bacterial keratitis, and one of the most common causes of bacterial keratitis overall. In one meta-analysis, prevalence of P. aeruginosa isolates in bacterial keratitis ranged from 6.8 to 55%.
It is widely known that pseudomonas keratitis is strongly associated with contact lens wear. In one study, incidence of pseudomonas keratitis was 2.76 cases per 10000 individuals per year, but rose to 13.04 cases per 10000 individuals when only considering contact lens wearers. In the same study, 55% of cases of pseudomonas keratitis were associated with contact lens wear.
Extended contact lens use allows adhesion of P. aeruginosa to contact lens surfaces and subsequently the cornea. P. aeruginosa possesses specific virulence factors, including pili, glycocalyx, and exotoxins, which allow adherence and invasion into the cornea.
Pseudomonas keratitis in non-contact lens wearers tends to occur more commonly in the elderly and also causes significant morbidity. Worse initial visual acuity, older age, and size and extent of stromal involvment appear to be associated with worse outcomes in non-contact lens wearers.
Diagnosis and treatment
All cases of suspected pseudomonas keratitis should be scraped and cultured. Treatment for pseudomonas keratitis is generally monotherapy with a fluoroquinolone eyedrop such as ciprofloxacin or moxifloxacin. Studies have shown fluoroquinolone monotherapy is non-inferior and has fewer side effects compared to combined tobramycin-cefazolin. Other choices include fortified aminoglycosides such as tobramycin.
While progression to endophthalmitis is rare, Pseudomonas is commonly cited as the causative pathogen of microbial keratitis leading to endophthalmitis leading to evisceration or enucleation. 
Steroid use in conjunction with antibiotics is controversial in the setting of pseudomonas keratitis as well as microbial keratitis as a whole. On subgroup analysis on patients from the steroids for corneal ulcers trial (SCUT), showed that pseudomonas ulcers had no overall benefit with the addition of corticosteroids. However, the same study showed that the invasive subtype of P. aeruginosa may demonstrate a small improvement in visual acuity with steroids versus placebo.
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