Comparison of clinical and microbiological profiles in smear-positive and smear-negative cases of suspected microbial keratitis.

PURPOSE: To examine the hypothesis that initial smear examination results have a significant bearing on the management and outcome of suspected microbial keratitis. MATERIALS AND METHODS: One hundred and seventy consecutive patients with suspected microbial keratitis were included in a prospective nonrandomized comparative study and their detailed clinical and microbiological data (smears and cultures of corneal scrapings) were captured on a predesigned corneal ulcer database. Patients were divided into two groups: Group 1 included 68 patients with corneal scrapings negative in smears while Group 2 included 102 patients with corneal scrapings positive in smears. The two groups were compared for their clinico-microbiological profile, management and clinical outcome. The outcome was noted at three months. Fisher's exact test was applied for statistical analysis. RESULTS: Cultures were sterile in 57.3% of patients in Group 1 compared to 17.6% in Group 2. Scrapings that grew S. pneumoniae, gram-negative organisms, fungi and Acanthamoeba were more often positive in smears (18.6%, 11.8%, 19.6% and 2.9% respectively). While data on duration of prior treatment was not available, prior medication made no significant difference to smear results. More (79.3%) patients of Group 1 had small infiltrate size ( CONCLUSIONS: Initial smear examination helps in instituting specific therapy thereby improving the outcome in cases of microbial keratitis. Positive smears indicate greater severity of disease and prior medication may not be a significant cause of smear negativity.

Is the cystatin-like domain of TSL functionally active in external ocular infections and during the normal diurnal cycle?

PURPOSE: To test whether the cystatin-like functional domain in tear specific lipocalin (TSL) is functionally active in tears during the normal diurnal cycle and during external ocular infections. METHODS: Capillary tube collected reflex (RTF), open (OTF) and closed (CTF) eye tear samples were recovered from six normals and semi-quantitatively western blot assayed for cystatin C and TSL. CTF samples were immunoprecipitated with antibodies raised against TSL, cystatin C and other antiproteases and screened for the co-precipitation of proteases by casein and gelatin zymography. OTF samples recovered from individuals with viral, fungal and bacterial keratitis were similarly screened for TSL-bound proteases. Human tissue was subjected to immunohistochemical study. RESULTS: Western blot analysis reveals a progressive increase in cystatin C in going from RTF to OTF to CTF samples (approximately 3, 7 and 30 ng microl(-1), respectively). In contrast, the concentration of TSL remains constant (approximately 1500 ng microl(-1)). Immunocytochemistry data show staining of the apical surface of the human conjunctiva and some intra-cellular staining for cystatin C, but not for cystatin A. Zymography confirms earlier data that CTF contains exceptionally high levels of proteases bound to a wide range of specific inhibitors. However, only trace amounts of proteases are complexed with cystatin C and no protease can be detected bound to TSL in either the pathological or CTF samples. CONCLUSION: Although TSL contains a functional cystatin-like domain, it is not physiologically active during the normal diurnal cycle or during external ocular infections. Reactive proteases in CTF are most likely controlled by the presence of excess levels of more reactive cystatins, especially cystatin C, which accumulates during prolonged eye closure. Immunohistochemical data suggest that the apical conjunctiva may be a contributing source for the accumulating cystatin C.