| Background and ObjectiveMycotic keratitis is a severe infectious diseases leading to the blindness of eye, especially in developing countries, also in china. Dr. Leber reported the mycotic keratitis in 1879 for the first time. Since the 1960s, due to the widespread application of antibiotics and corticosteroids, and with the increase of contact lens and improvement of diagnostic techniques, the incidence of mycotic keratitis has increased year by year. The common pathopoiesis fungus in China is Fusarium Solani (FS) and Aspergillus Fumigatus (AF), but Candida Albicans (CA) is common in developed countries. In China, there are many people engaged in agriculture. Therefore, when they are working in farm, their eyes are potentially subject to trauma made by agricultural factors especially for the factors of vegetality. Then, this trauma can provide a chance of fungus implantation on cornea, which causes to infection. At present, because the drug therapeutic efficacy for mycotic keratitis is poor, and other several unfavorable factors, such as limited donors for corneal transplantation and the mycotic keratitis recur easily after corneal transplantation and so on. Many patients are suffered from loss of eyesight and extirpation of eyeball even. Nowadays, more and more internal and external scholars are paying close attention to the increasing morbidity of mycotic keratitis. The mycotic keratitis has already become the hot topic in the study of infectious keratopathy. In the past, many researches were more focusing on the areas of the segregation and identification of pathomycetes and the clinical diagnosis of mycotic keratitis, and treatment for mycotic keratitis. There are still lack of reliable animal model of mycotic keratitis, and only few researches on pathogenesis of mycotic keratitis. It is also remain unclear that the pathogenic mechanism of corticosteroid influencing the mycotic keratitis.The aim of our study is to establish the animal model of human mycotic keratitis, and to observe the natural process. Histopathology and cultivation of pathogen are carried out on different phase, and the propagation of fungus is researched in the development of mycotic keratitis. Moreover, the influence of corticosteroid on the growth of fungus and clinical situation development of mycotic keratitis are studied, in order to provide experimental evidence for the clinical research of mycotic keratitis.Materials and methods1. Two kinds of standard strain were choosed for innoculation, Fusarium Solani (FS) and Aspergillus Fumigatus (AF). Two sorts of mouse models of mycotic keratitis were established by corneal scarification with above-mentioned strain respectively. Each kind of keratitis model has fifty eyes. Then, the pathological changes in cornea were observed by slit-lamp biomicroscope everyday. Scraping of abnormal cornea for staining and cultivation and identification of strains in cornea were performed at 1,4, 6, 8, 14 days in the process of mycotic keratitis. The growth mode of fungus in cornea and responses of corneal tissue were observed by histopathology.2. The animal models of mycotic keratitis were established by corneal scarification with above-mentioned strain respectively. 244 mice were randomly divided into 4 experimental groups and 1 blank group, and 56 mice for each experimental group and 20 mice in blank group. FS were inoculated on the mice in the group 1 and group 2, and AF were inoculated in group 3 and group 4, and physiological saline (PS ) for the blank group. Group 2, group 4 and the blank group were treated with 0.5% dexamethasone drops for 3 days after inoculation, and the influence of corticosteroid on mycotic keratitis were observed at 2, 4, 8 and 14 days after infection.3. Statistical analysis: All the experimental data were processed by SPSS13.0 software. The corresponding 95% confidence intervals (CI) were estimated. A P values less than 0.05 was considered statistically significant. All reported P values are evaluated by 2 sides. Nonparametric test was used to analyze clinic score of every group, and t test was used to analyze analytic result of pathology.Results1. The keratitis model of FS is established for success in 90%. The typical appearance of mycotic keratitis can be seen at 2 days after innoculation. The fungus growth in anterior layer of corneal stroma examined by histopathology 4 days after innolation, and the reparation of corneal epithelium in some keratitis model also can be observed. Then, from 8 days, the neovascular can be seen invasion from the limbus of cornea. The positive rate of cultivation of fungus is 90%, 70% and 50% at 4, 8 and 14 days respectively. On the contrary, the keratitis model of AF is established for success in 100%. After innoculation, the inflammatory reaction and necrosis of cornea are more severe, and the pathogenetic condition of keratitis develops fast. From 9 days, the neovascular can be seen invasion from the limbus of cornea. The positive rate of cultivation of fungus is 100%, 70% and 50% at 4, 8 and 14 days respectively. There still can be seen fungus in pathological section of corneal tissue at 14 days.2. Compared with untreated group and blank group during two weeks after innoculation, the course of mycotic keratitis was extended and showed more severe pathological manifestation in dexamethasone-treated group (P<0.05). The loading dose and invasiveness of mycetes in cornea of dexamethasone-treated mice increased more (P<0.05). Under the influence of corticosteroid, the hyphae of fungus in cornea was thick. The hyphae of FS grow in parallel with cornea layer and infiltrated deep in the cornea layer further. Finally, the hyphae approached and penetrated the corneal endothelium gradually. On the contrary, the hyphae of AF grow in a great mess and develop to deep lamella of cornea, which destroyed the layers of cornea obviously.ConclusionsThe cornea] scarification without immunodepressant is adopted which can successfully establish the animal model for simulating human mycotic keratitis of natural infection. The application of corticosteroid can aggravate the pathogenetic condition of mycotic keratitis and extend the course of disease by increasing invasive power and productivity of fungus, without changing the growth pattern of fungus.
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