Two hundred thirty consecutive cases of presumed infectious keratitis were reviewed. Cultures were positive in 49.5% (114 of 230). Acridine orange stain sensitivity (81%) was significantly greater than gram stain sensitivity (65%) (p < 0.002). Gram stain specificity was 92%, and acridine orange specificity was 89%. In keratitis with low or moderate growth, acridine orange was positive in 73% (61 of 84) as compared with Gram stain 53% (45 of 84), (p < 0.001). In cases of heavy microbial growth, Gram stain was positive in 97% (29 of 30), acridine orange in 100% (30 of 30). This study demonstrates that both Gram stain and acridine orange stain are excellent in cases of infectious keratitis with heavy microbial growth, but that acridine orange is significantly better than Gram stain in cases with low amounts of organisms.
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