Differential diagnosis between experimental endophthalmitis and uveitis in vitreous with Raman spectroscopy and principal components analysis.

Raman spectroscopy has been used for the diagnosis of various eye diseases. A diagnostic tool based on Raman spectroscopy has been developed to discriminate endophthalmitis from uveitis in vitreous tissues of rabbits' eyes in vitro. Twenty-two New Zealand rabbits suffering from endophthalmitis induced by Staphylococcus aureus (n=10), non-infectious uveitis induced by lipopolysaccharide from Escherichia coli (LPS) (n=10 animals) and control (n=2) were included in the study. After eye inoculation, vitreous tissues were dissected and a fragment was submitted to dispersive Raman spectroscopy using near-infrared laser excitation (830 nm, 100 mW) and spectrograph/CCD camera for detection of Raman signal with integration time of 50 s. A routine was developed to classify the spectra of endophthalmitis and uveitis using principal components analysis (PCA) and Mahalanobis distance. The mean Raman spectra of tissues with uveitis and endophthalmitis showed several bands in the region of 800-1800 cm(-1), which have been attributed to nucleic acids, amino acids and proteins from inflamed tissue and proliferating bacteria. The bands at 1004, 1258, 1339, 1451 and 1635 cm(-1) showed statistically significant differences between both diseases. It was observed that principal components PC1, PC3 and PC4 showed statistically significant differences for the two tissue types, indicating that these PCs can be used to discriminate between the two groups. The diagnostic model showed 94% sensitivity, 95% specificity and 95% accuracy using PC3×PC4. The Raman spectroscopy technique has been shown to be useful in differentiating uveitis and endophthalmitis in vitreous tissues in vitro, and these results may be clinically relevant for differentiating vitreous tissues to optimise the diagnosis of inflammatory and infectious vitreoretinal diseases.