Raman spectroscopy on human tear films: Healthy subjects vs Amyothrophic Lateral Sclerosis patients
Purpose: To characterize the tear composition by Raman spectroscopy looking for Amyotrophic Lateral Sclerosis (ALS) biomarkers.
Method: Raman spectroscopy was used to analyse tears of nine healthy subjects (CTRL group, 57±10 years, 5 males) and tears of thirteen ALS patients (ALS group, 65±14 years, 8 males). A few microliters of tear were extracted from each subject with a capillary tube, the drop was deposited on a BaF2 substrate, and dehydrated in a controlled environment. The heterogeneous pattern (spherules, ferns, etc.) was measured at different points using a laser of 532 nm wavelength, 6 mW power, and 1 micrometre spot. Measurements were performed in the 150-1800 cm-1 range.
Results: Raman spectra clearly showed the peaks of phenylalanine and urea (1005 cm-1), C-H deformation (1450 cm-1), guanine and adenine ring stretching (1575 cm-1), and amide I (1670 cm-1), in addition to many other smaller structures. In all the areas (spherules, ferns, etc.), the mentioned peaks were on average more intense in the ALS group, up to more than 80% for the peak at 1450 cm-1 in the areas where the spectra showed the best signal/noise ratio (i.e. spherules, ferns, and in a flat area at the edge of the drop). After normalizing the average spectra of the two groups at the intensity of the 1005 cm-1 peak, the other three peaks remained more intense in the ALS than in the CTRL group.
Conclusions: Raman spectroscopy can provide information on the tear composition, on its variations due to different possible variables (biological or environmental factors, contact lens wear, etc.), and potentially also for the diagnosis of pathologies through biomarkers. An example is the level of urea, according to literature analyses carried out on blood samples and according to these first results on tears of ALS patients.
Biography: Alessandro Duse received his Bachelor’s Degree in Optics and Optometry in May 2019 at the University of Milano-Bicocca. In 2019 he obtained a scholarship at the Department of Materials Science to work in the field of Raman spectroscopy applied to the tear film, continuing the thesis project. After graduating, he also collaborated on other optometry projects of the research group, such as the validation of digital methods for measuring contrast sensitivity. He held a position of contract professor for both Advanced Optometry and Geometrical Optics at the University of Milano-Bicocca. He also works as an optometrist in the family business.
*Data correct at the time of submission to BCLA by NCC.