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N. M. Buchser, S. R. Dubovy, D. Miller; Detection of Organisms by Microbiology vs. Histopathology in Corneal Biopsy and Penetrating Keratoplasty Specimens. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5119.
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Detection of the causative organism is important for successful management of keratitis. Microbiologic culture is the conventional method to identify organisms. However, histopathologic analysis can also detect organisms in patients who undergo corneal biopsy or penetrating keratoplasty (PK). The purpose of this study is to compare the detection of organisms by microbiology (culture) and histopathology (slides) in corneal biopsies and corneal buttons removed by PK.
Records from the Bascom Palmer Eye Institute microbiology and histopathology laboratories were retrospectively searched for patients who underwent PK or corneal biopsy for keratitis and had specimens bisected and submitted for both microbiologic and histopathologic evaluation between January 1, 1996 and October 15, 2008. Detection of bacteria, fungi, protozoa, and mycobacteria by these two methods were compared.
425 total specimens were documented, including 42 corneal biopsies and 383 PK specimens. No organisms were detected in either slides or culture in 55% of specimens. These tests both identified organisms in 17%. Cultures were positive, but slides did not detect organisms in 19%. Organisms were identified on slides, but cultures were negative in 10%. Of the 193 cases in which organisms were identified, 43% were fungi, 39% bacteria, 14% protozoa, and 4% mycobacteria. Cultures detected bacteria, fungi, protozoa, and mycobacteria in 52%, 26%, 3%, and 2% of cases, respectively. Histopathology allowed the additional detection of 14%, 19%, 11%, and 2% of bacteria, fungi, protozoa, and mycobacteria, respectively. Culture identified more bacteria than histopathology (p<0.001). Histopathology detected more protozoa than culture (p=0.057). Both tests were similar in their detection of fungi and mycobacteria.
Microbiology and histopathology are complimentary tests to detect organisms in corneal tissue. Microbiology is better in detecting bacteria, while histopathology is better in detecting protozoa. Identification of fungi and mycobacteria is comparable for both tests. Submission of corneal tissue for both microbiologic and histopathologic analysis is recommended to identify the cause of infectious keratitis.
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