Raman spectroscopy of human vitreous in proliferative diabetic retinopathy.

PURPOSE Recent studies have demonstrated increased nonenzymatic glycation in vitreous from patients with diabetic retinopathy. The present study reports the use of Raman spectroscopy as a novel approach for investigating these molecular changes in human vitreous and experimental tissues. METHODS Near-infrared laser-excited Fourier-transform (FT) Raman spectroscopy (RS) was performed on vitreous specimens obtained at surgery from seven patients with proliferative diabetic retinopathy and from 10 controls. Measurements were also obtained from samples of control and glycated (in vitro) rat tail tendon collagen and demineralized chick bone collagen. RESULTS Spectroscopy of vitreous samples from patients with diabetic retinopathy revealed two prominent peaks at 1604 cm-1 and 3057 cm-1, corresponding to aromatic C = C and C-H stretching vibrations in pi-conjugated and aromatic molecules. The peak at 1604 cm-1 was threefold higher in vitreous from patients with diabetes than from controls. Spectra obtained from experimental tissues provided evidence suggesting that the results obtained in human vitreous may be due to nonenzymatic glycation and not to the lysyl oxidase pathway. CONCLUSIONS These findings suggest that human vitreous obtained from subjects with diabetes may be distinguished from control vitreous by FT-RS and that the peaks characterizing the diabetic samples are possibly due to nonenzymatic glycation. Raman spectroscopy may provide a useful method to elucidate the molecular events underlying these abnormalities.