PURPOSE. The aim of this study was to use Raman spectra of tears to differentiate between infectious and noninfectious ulcerative keratitis. METHODS. Raman microspectroscopy was applied using the drop-coating deposition method on Ti/Au-coated glass slides to obtain sample spectra from different human tear groups, including tears from healthy subjects and from patients with infectious and noninfectious ulcerative keratitis. By comparing the difference spectra of the groups, the authors identified local Raman features useful for differentiation of ulcerative keratitis. Principal components (PCs) of normal tears were used as affined spectral coordinates. After performing projections of Raman spectra of both infectious and noninfectious tear samples, the authors compared the two groups to identify global spectral parameters with differential statistical significance. RESULTS. Differentiation between infectious and noninfectious ulcerative keratitis might be made directly through observation of the normalized tear Raman spectra or the transformed principal scores. Spectral segments with differential statistical significance included 878~888 cm -1, 885~888 cm -1, 945~993 cm -1, 1007~1015 cm -1, 1074~1100 cm -1, 1090~1094 cm -1, 1096~1099 cm -1, 1386~1403 cm -1, 1463~1469 cm -1, 1469~1473 cm -1, 1557~1563 cm -1, 1584~1588 cm -1, and 1614~1621 cm -1. There were two PCs with statistically significant differences for the two groups of ulcerative keratitis, PC1 (P = 0.01) and PC2 (P = 0.05). CONCLUSIONS. This novel approach using the analysis of Raman spectra of teardrop samples for differentiation of ulcerative keratitis demonstrates the potential application of Raman microspectroscopy for clinical practice. This technology should complement the conventional cytological method for rapid diagnosis in the clinician's office.
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