الفهرس 
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Abstract
Fungal keratitis is not a common cause of corneal infection, but it represents one of the major causes of infectious keratitis in tropical areas of the world. Considering fungus as a possible cause of infectious keratitis is important because devastating ocular damage can result if it is not diagnosed and treated promptly and effectively 1.
Fungal keratitis remains a diagnostic and therapeutic challenge to the ophthalmologists.The challenge is in establishing a clinical diagnosis, isolating the etiologic fungal organism in the laboratory, and treating the keratitis effectively with antifungal agents. Unfortunately, delayed diagnosis is common, primarily because of lack of suspicion. Even if the diagnosis is made accurately management remains a challenge because of the poor corneal penetration, and the limited commercial availability of antifungal agents 2.
Fungi gain access into the corneal stroma usually through a defect in the epithelium. The epithelial defect usually results from trauma (e.g, contact lens wear, vegetable or organic matter, prior corneal surgery), and then the organism multiply and cause tissue necrosis and an inflammatory reaction 3.
Laboratory investigative modalities for fungal ulcer confirm the clinical diagnosis and provide supportive evidence for planning therapy . Corneal scraping with corneal biopsy and microbial culture are most common laboratory investigation used. Recently the impression cytology has been introduced as a diagnostic modality for corneal ulcer 4.
Impression cytology was first introduced in Ophthalmology by Egbert et al on 1977 5 .They reported the possibility of removing the cells from the surface of the epithelium by pressing a cellulose acetate filter paper on the bulbar conjunctiva. Impression cytology has been used to diagnosis dry eye conditions such as vitamin A deficiency, contact lens wear, chemical , thermal burns, limbitis, herpes simplex keratitis and acanthamoeba keratitis 6 . Varde and Biswas on 20097 have conducted study on the impression cytology on ocular surface tumor and reported that the impression technique in the diagnosis and follow – up the lesion. It gives quick results, noninvasive and cost-effective and helpful in obtaining specimen materials from small lesions, which are otherwise difficult by the conventional techniques of mechanical scraping 7. With scraping the infected cells as well as some surrounding normal cells are removed and there is risk of corneal perforation especially in impending perforation. Corneal biopsy are used only in cases where, scrapings for direct microscopic and culture are negative ,it is of greet value and gives a suggestion of nature of the offending microbe, but can induce irregular astigmatism. Also, corneal perforation can occur 8.
The impression smear technique relies on cellular adherece to the filter paper rather than mechanical abrasion of the subepithelial areas . In contrast , when filter paper is applied to the corneal lesion ,only the affected cells are removed and no risk for corneal perforation, so with impression smear all of the disadvantages of other investigative modalities are overcome especially in cases of impending corneal perforation 1.