Multimodal optical coherence tomography, Raman spectroscopy and IR fundus imaging for in vivo retinal imaging

Despite the vast clinical acceptance of optical coherence tomography in visualizing the structure and vasculature system (angiography) of the retina, the method is still lacking the capability to provide molecular fingerprints of retinal tissue. The assessment of biochemical changes would critically enhance the early disease diagnostics when treatment is most effective. In recent years Raman spectroscopy has been recognized as an extremely powerful tool for bioanalytical and biomedical applications because the method provides molecular fingerprint information of the molecular structure and biochemical composition of cells and tissues without external markers. Diseases and other pathological anomalies are accompanied by changes in these properties. The processing of chemically-specific tissue Raman spectra via mathematical approaches for a spectral analysis and classification enables an objective evaluation of the tissue samples for an early disease diagnosis. Due to its non-invasiveness, Raman spectroscopy also offers the potential for in vivo tissue screening to reliably diagnose and screen cancer and other diseases on the molecularly-specific level. However, the application of Raman spectroscopy under in vivo conditions is extremely challenging due to the delicate nature of eyes. When dealing with biological samples fluorescence interference is best avoided by using Raman excitation wavelengths in the NIR region. A recent breakthrough was to show that relevant Raman spectra can be recorded from human retinal tissue under in-vivo conditions, i.e., given the laser safety constraints and the light collection limitation through the eye’s pupil. In this work, combined swept source optical coherence tomography and OCT angiography operating at 1060nm, and Raman spectroscopy at 790nm was realized as an ophthalmic device. The device is also equipped with an infrared tracking system to assure that the Raman acquisition is collected from a specified position. The optical coherence tomography scans are used as a reference to identify positions showing structural abnormalities in the retina to later collect the Raman spectra. The recorded Raman spectra are processed and analyzed to distinguish between the healthy and diseased retina.