FEB 2014

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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Page 68 of 114

E W FEATURE 66 by Maxine Lipner EyeWorld Senior Contributing Writer Counterculture Considering PCR for infectious keratitis diagnosis I nfectious keratitis is a widely seen problem with about 70,000 corneal ulcers occurring each year in the United States, according to Bennie H. Jeng, MD, professor and chair, Depart- ment of Ophthalmology and Visual Sciences, University of Maryland, Baltimore. Determining exactly what the causative organism of the ulcer is and how to best treat this has fallen to doing cultures and often guessing at what medication might work, while waiting for results. But what if you could deter- mine exactly what corneal infection to treat while the patient remains in the office? Such is the promise of PCR testing. "You may be able identify the organism within an hour or so and then you can hold the patient and start targeted therapy rather than u sing shotgun therapy," Dr. Jeng said. In particular, he thinks that it would be efficacious to identify fungal keratitis organisms this way. "In general the teaching is that you don't want to start antifungals until you have confirmation, whether it is by culture, or gram stain or confocal (microscopy), for a number of rea- s ons," Dr. Jeng said. "The antifun- gals are toxic and they're hard to come by, so you don't want to start them without knowing for sure the organism in question." Something like PCR, he thinks, would allow practitioners to promptly start appropriate therapy without worry- ing about this. Culture negatives Alfonso Iovieno, MD, consultant ophthalmologist, Arcispedale Santa Maria Nuova, Reggio Emilia and University Campus Bio-Medico, Rome, pointed out that while traditional microbiology remains the cornerstone of infectious keratitis, it has its shortcomings. "We know from the literature that the sensitiv- ity of culture methods on corneal scrapings is quite poor, with as high as 40 to 60% false negatives," he said. In cases of rare or fastidious micro-organisms, this is particularly important, Dr. Iovieno finds. In ad- dition, those doing the culturing can play a key role. "Ophthalmic micro- biology requires specific expertise with a rather long learning curve and dedicated personnel," he said. Dr. Jeng agreed that with tradi- tional culturing there can be a high percentage of false negatives in infectious keratitis, for a variety of reasons. These take time to grow. "Generally, we will wait two or three days for bacterial cultures," Dr. Jeng said. "Fungal cultures we'll wait one week to 10 days." The yield for these fungal cultures, he finds, is even lower than with bacterial, which in the end may not grow even when there are infectious organisms pres- ent. Sometimes after the wait, the culture still doesn't grow due to technique, inadequate sample, or other factors such as if the patient has been treated with antibiotics prior to presentation, he explained. PCR at work Potentially, PCR testing can over- come many of these issues, Dr. Iovieno said. "PCR is considered the gold standard in infectious diagnosis as it has the highest specificity and February 2011 Corneal infections February 2014 T he EyeWorld Monthly Pulse survey for February focused on corneal infections. When asked what treatment they would provide for a patient with an epithelial defect from an episode of recurrent corneal erosion syndrome, the majority of respondents (61.1%) said they would place a bandage contact lens with prophylactic topical antibiotics. Only 8.5% of respondents said they would patch the eye. Other options were to treat with lubrication alone (11.3%) and treat with lubrication and prophylactic topical antibiotics (19%). For patients with symptoms of dry eye and findings of inflammation of the meibomian glands that are not improved after using hot compresses, lid hygiene, and/or topical steroids and antibiotics, Monthly Pulse Keeping a Pulse on Ophthalmology most (64%) said they would prescribe oral doxycycline. For those who perform corneal ulcer scrapings, 54.6% said positive organisms were identified less than 50% of the time, while 44.6% of respondents said a positive organism is identi- fied more than 50% of the time. Eighty-five percent of respondents said if they needed a cornea transplant, they would prefer "all of the above," which included preferring that the surgeon use the technique he or she is most comfortable with, preferring that the surgeon use the technique with the lowest risk of rejection, and preferring that the surgeon use the technique with the lowest potential for intraoperative and postoperative complications. AT A GLANCE • Culturing for infectious keratitis c an be slow and may lead to false negative results. • Sensitivity is one of the strengths of PCR testing. If even a little DNA is present, this can be amplified and identified. • Some practitioners believe that PCR testing may hold particular promise for difficult to detect corneal infections such as Mycobacteria, Acanthamoeba, and HSV. Acanthamoeba sclerokeratitis 56-68 Feature_EW February 2014-DL2_Layout 1 1/30/14 10:45 AM Page 66

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