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V. Felcida, A. K. Jain, A. Gupta, S. Pilli; Evaluation of Impression Smear in Diagosing Fungal Keratitis. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2685.
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Infective keratitis is a major cause of corneal blindness in the developing countries.Diagnosis and treatment of fungal keratitis is one of the most difficult problems encountered by ophthalmologists.The key to the successful management of any case of fungal keratitis lies in the early diagnosis and immediate initiation of antifungal treatment.
Our study included 50 clinically suspected cases of fungal keratitis. Patients suffering from bacterial keratitis and those already on treatment with antifungal drugs were excluded Method : Xylocaine (4%) eye drops were instilled, following which 3×5mm precut and autoclaved strips of cellulose acetate filter paper [GSWP 02500 millipore, 0.22mµ4 pore size] was applied to the lesion. The filter paper strip was gently pressed for 5 seconds .The filter paper was immediately transferred on the surface of autoclaved glass slides and gently peeled off leaving the impression on the slides and the slides were fixed in 95% alcohol and then stained with haematoxylin-eosin (H&E) and periodic acid Schiff (PAS) and direct microscopy with 10 % KOH. All patients’ mechanical corneal scrapings were also seen under direct microscopy with 10 % KOH. Cases were diagnosed to be having fungal keratitis if patients responded to antifungal treatment, were KOH smear positive, PAS / H&E positive for fungi
Our study included 50 patients.In six of our patients impression smear proved to be a therapeutic adjunct as the lesion came out in toto when impression smear was taken.In our study KOH +CFW staining from impression smear technique were positive in 36 (72%) patients .KOH staining form direct corneal scrapings were positive in 35 patients (70%). The sensitivity of impression smear technique keeping gold standard as KOH positivity from conventional mechanical corneal scraping was 97.14 %.The specificity of the technique was 92.86 %.
The impression smear technique relies on cellular adherence rather than mechanicanl abrasion .Therefore there is a little chance of damage to these structures or to the adjacent epithelium. It has a valuable place as an adjunct therapy because it removes some lesions in toto.Impression smear technique is atraumatic and simple to perform repeat impression smear can be used as a debridement technique to reduce the organismal load.We recommend impression smear as a technique for early diagnosis of suspected fungal keratitis as it can be done in the periphery without slit lamp and chances of corneal perforation are nil as no needle or knife is used
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