The Clinical Diagnosis of Microbial Keratitis

Abstract

Purpose-To evaluate the ability of ophthalmologists to predict the laboratory results of presumed microbial keratitis and to explore which findings might influence diagnostic prognostication. Design-Prospective cross-sectional study.Methods-Fifteen ophthalmologists completed study forms at the initial presentation of patients with presumed microbial keratitis. After predicting the category of microbial recovery, clinicians submitted corneal scrapings for masked laboratory processing. The relative effects of ocular inflammatory signs on correct microbial diagnosis were explored with Poisson regression.Results-Clinical examiners correctly predicted the presence or absence of microbial recovery in 79 (76%) of 104 ulcerative keratitis and successfully distinguished among bacterial, fungal, and amoebic keratitis for 54 (73%) of 74 culture-positive infections, although only 31 (42%) were properly subcategorized. The positive predictive value of clinical diagnosis was 65% (95% confidence interval (CI), 43%-84%) for 20 eyes with Pseudomonas keratitis, 48% (95% CI, 32%-63%) for 38 other bacterial keratitis, 45% (95% CI, 17%-77%) for 13 fungal keratitis, and 89% (95% CI, 52%-100%) for nine Acanthamoeba keratitis. The recognition of Pseudomonas keratitis was significantly improved by the occurrence of a larger infiltrate (P = .02), and correctly predicting Acanthamoeba keratitis was enhanced by observing a ring infiltrate (P < .001). Antimicrobial use before referral significantly attenuated clinical diagnosis (P = 0.03) and hampered microbial recovery (P = 0.004). Conclusions-EstablishedPseudomonas keratitis and Acanthamoeba keratitis can be suspected before laboratory confirmation, but overlapping inflammatory features and recent empiric antimicrobial treatment limits etiologic recognition of most microbial corneal infections.The clinical diagnosis of microbial keratitis often relies on a history of infectious exposure and the morphological features of corneal inflammation. 1 Ophthalmologists use clinical clues to recognize ocular surface infection, 2 and some distinctive though not pathognomonic signs may help to differentiate bacterial, fungal, and amoebic pathogens of the cornea. 3-5Laboratory demonstration of the infective agent in a corneal sample is recommended 6 but may not be regularly obtained due to time, cost, and availability. 7, 8 Initial antimicrobial therapy is often guided by subjective interpretation of presenting clinical features. 9 We aimed to determine the predictive value of ophthalmologists' opinions about presumed microbial keratitis before microbiological tests were known. We also sought to identify which findings Inquiries to Kirk R. Wilhelmus, MD, Sid W. Richardson Ocular Microbiology Laboratory, Cullen Eye Institute, 6565 Fannin Street, Baylor College of Medicine, Houston, TX 77030; fax: 713-798-4142; e-mail: kirkw@bcm.tmc.edu Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this ...

Comparative Study of Gram Stain, Potassium Hydroxide Smear, Culture and Nested PCR in the Diagnosis of Fungal Keratitis

“…Dahlgren et al [5] reported that clinical examiners correctly predicted the presence or absence of microbial recovery in 79 (76%) of 104 ulcerative keratitis cases. The positive predictive value of clinical diagnosis was 45% (95% confidence interval 17-77%) for 13 FK [5] .…”

“…Since clinically it is difficult to establish a definitive diagnosis of FK, the final diagnosis is largely dependent upon a combination of clinical and microbiological results [5] .…”

Mycotic Keratitis, a State-of-the-art Review

“…This may result in corneal perforation, and Keratoplasty is performed. As the appearance of the ulceration for distinguishing fungal from bacterial ulcer is unreliable (45) and since resistant fungi have been reported (33,46), treatment on the basis of correct identification of pathogen by culture and determination of sensitivity could have better outcomes than empirical treatment with broad-spectrum antibiotics. Culture results are also critical to tailor therapy for patients who fail empirical therapy.…”

Current Thoughts in Fungal Keratitis: Diagnosis and Treatment

“…However, only 31 (42 %) were subcategorized properly, suggesting the notion that although infections can be detected, overlapping clinical features of the etiologic agents of keratitis makes it difficult to distinguish one from another. 22 Therefore, tissue sampling and culture continues to be an imperative utility in the diagnosis of fungal keratitis. Because of predilection of fungi to penetrate into deeper layers of the cornea, tissue swabbing is usually inadequate in confirming a fungal agent.…”