Targeting the molecular information of the retina with Raman spectroscopy

Abstract

Purpose : Despite its potential in providing molecular fingerprint information of cells and tissues, Raman spectroscopy has not been widely explored in ophthalmology. The main constraints are given by low signal collection efficiency due to limited incident optical power and pupil size of the human eye. Here we validated the performance of a multimodal ophthalmic imaging device that includes Raman spectroscopy for probing the human eye in vivo in a clinical setting.

Methods : The custom-built device included IR fundus imaging (at 730 nm), swept-source optical coherence tomography (SS-OCT at 1060 nm) and Raman spectroscopy (RS at 785 nm with 1 mW excitation power). The IR fundus imaging module was used to align the device to the subject’s eye. The OCT en face image was generated almost instantaneously to allow position selection for the Raman spectroscopy measurement. Prior to human in vivo measurement, we validated the performance of the device by measuring a multimodal eye model and an in vivo albino rat. For the rat measurement, we modified the system to take into account the small pupil size of the rat.

Results : The multimodal eye model was measured by using IR fundus imaging (Fig. 1a), SS-OCT (1b shows the the B-Scan at the horizontal position marked by the yellow dotted line) and Raman spectroscopy (1c shows the Raman signal at the background and the vessel-like structure position, shown as a blue dot and a red dot (1a), respectively). The en face OCT of the albino rat is shown in Fig. 2a. The Raman spectroscopy measurements of the area outside the ONH (average of 12 spectra, blue dots) and the area inside the ONH (average of 3 spectra, red dot) is shown in Fig. 2b. The peaks around 1250 cm^-1, 1450 cm^-1 and 1650 cm^-1 correspond to the Raman bands of Amide III, δ(CH₂) and Amide I, respectively, which indicate the presence of collagen, protein and lipid.

Conclusions : We presented performance validation of a clinical multimodal ophthalmic imaging device with the ability to perform in vivo Raman spectroscopy, using an eye model and rat imaging. The device provided interpretable molecular information based on the Raman method even with low excitation power. This encourages the investigation of human in vivo retina Raman measurements for various retinal and neurological diseases.

This abstract was presented at the 2023 ARVO Imaging in the Eye Conference, held in New Orleans, LA, April 21-22, 2023.

 

Fig. 1. Measurement results of the multimodal eye model. Scale bar: 1 mm

 

Fig. 2. Measurement results of the in vivo albino rat. Scale bar: 500 µm