Pseudomonas aeruginosa is a common inhabitant of soil, water and vegetation, and often is associated with bacterial infection secondary to a vegetation-related corneal insult.1 In fact, several reports indicated that Pseudomonas was more likely to cause infection following a vegetation injury than fungal infiltrates.1 Pseudomonas also has a relatively complex genetic makeup, which permits it to survive fairly easily in a variety of outdoor and indoor environments.2
In North America, the incidence of microbial keratitis (MK) secondary to Pseudomonas is 2.76 cases per 10,000 individuals a year.3 However, when considering only contact lens wearers, this number increases dramatically to 13.04 cases per 10,000 individuals a year.3 In other words, contact lens patients are more than nine times as likely to develop a Pseudomonas infection as those who don’t wear contacts.
Why CL Patients?
Pseudomonas aeruginosa is the most common bacterial cause of MK in contact lens wearers.4 But, why is that? One of the primary explanations is that Pseudomonas bacteria adhere to contact lens surfaces more easily than many other pathogens.5 More specifically, Pseudomonas bacteria often exhibit pili and flagella that can facilitate the adhesion processes.5 Within 24 hours of exposure, Pseudomonas microbes typically form a biofilm with the contact lens, which causes permanent, irreversible surface adhesion.6
Complicating this association, there is a non-piliated Pseudomonas aeruginosa strain that easily can adhere to the contact lens surface as well. Some researchers believe that this occurs due to surface hydrophobicity.2 (In short—the more hydrophobic the lens surface, the more likely the bacteria are to adhere.)
For several years, researchers suggested that increased lens wettability could help combat pathogen adhesion. However, more recent data indicated that, although certain surfactants yielded a small decrease in the binding rate of Pseudomonas bacteria, mean adhesion rates were not dramatically affected by contact lens surface wettability.7 Further, it is worth mentioning that this underlying binding process leads to the development of not only MK, but also corneal inflammatory events, infiltrative keratitis, contact lens-related acute red eye and contact lens peripheral ulcers.8
Topical Therapeutic Options
Given the virulence of Pseudomonas aeruginosa, an aggressive approach to therapeutic management is required. Contact lens patients who present with a grayish-white infiltrate, an overlying epithelial defect, a very inflamed eye, significant conjunctival injection, lid edema and an anterior chamber reaction often have MK secondary to Pseudomonas. These patients often will complain of an acute onset of significant pain, photophobia, discharge (sometimes only evident in the tear film under high magnification) and decreased vision.
Patients who present with ulcers located within 1mm of the central axis, multiple infiltrates, large infiltrates (>3mm) or a history recent ocular surgery should be cultured. Furthermore, immunocompromised patients who exhibit atypical ulcers (e.g., in the presence of a hypopyon or that cause significant tissue loss) should be cultured immediately and referred to a corneal specialist.
Initiate treatment with a broad-spectrum bacteriocidal agent, such as a topical fluoroquinolone every 30 minutes to hourly while awake and q2h at night. In severe cases, a fortified antibiotic, such as tobramycin 12.5mg/ml should be alternated with the fluoroquinolone. Cycloplegic agents will help minimize pain and photophobia. Also, after the first 24 hours of treatment, tobramycin ointment may be applied overnight.
Although some corneal specialists advocate topical corticosteroids to manage the severe inflammation and potential scarring caused by MK, you should use these agents with caution. In fact, topical corticosteroids are only appropriate if you have positively identified the underlying organism, confirmed that the pathogen is susceptible to the selected antibiotic, and determined that the patient has exhibited significant improvement since the initiation of treatment. And, if you confirm that the causative bacteria are Pseudomonas, do not consider steroid use until the patient has had 72 hours of antibiotic therapy.
Other treatment options include amniotic membrane transplantation. One study showed that this procedure was associated with immediate pain relief, lower density of the resultant corneal opacity and better uncorrected acuity at final follow-up.9
Based on the research, there are many reasons to be concerned about Pseudomonas aeruginosa infections in your contact lens patients—especially as this bacterial strain continues to mutate and evolve. Fortunately, newer anti-infective agents––such as besifloxacin––have specific indications for Pseudomonas isolates.
Nonetheless, it is your job to make a prompt diagnosis of any suspected infection in a contact lens patient. Then, you should initiate an aggressive treatment approach that includes frequent follow-up and/or comanagement with a corneal specialist. This approach will help protect the patient from prolonged ocular discomfort as well as help facilitate a good visual outcome.
Dr. Karpecki is a paid consultant and advisor to Bausch + Lomb and Bio-Tissue Inc. He has no direct financial interest in any of the products mentioned.
1. Norina TJ, Raihan S. Microbial keratitis: aetiological diagnosis and clinical features in patients admitted to Hospital University Sains Malaysia. Singapore Med J. 2008 Jan;49(1):67-71.
2. Bruinsma GM, van der Mei HC, Busscher HJ. Bacterial adhesion to surface hydrophilic and hydrophobic contact lenses. Biomaterials. 2001 Dec;22(24):3217-24.
3. Jeng Bh, Gritz DC.Epidemiology of ulcerative keratitis in northern California. Arch Ophthalmol. 2010 Aug;128(8):1022-8.
4. Willcox MD, Holden BA. Biosci Rep. 2001 Aug;21(4):445-61.
5. Duran JA, Refojo MF. Pseudomonas attachment to new hydrogel contact lenses. Arch Ophthalmol. 1987 Jan;105(1):106-9.
6. Marshall KC. Interfaces in Microbial Ecology. Cambridge, Mass: Harvard University Press; 1976:156.
7. Tran VB, Sung YS, Copley K, et al. Effects of aqueous polymeric surfactants on silicone-hydrogel soft contact lens wettability and bacterial adhesion of Pseudomonas aeruginosa. Cont Lens Anterior Eye. 2012 Aug;35(4):155-62.
8. Szczotka-Flynn LB, Pearlman E. Microbial contamination of contact lenses, lens care solutions, and their accessories: A literature review. Eye Contact Lens. 2010 Mar;36(2):116-29.
9. Kheirkhah A, Tabatabaei A, Zavareh MK, et al. A controlled study of amniotic membrane transplantation for acute Pseudomonas keratitis. Can J Ophthalmol. 2012 Jun;47(3):305-11.