Analysis of macular pigment carotenoids in human blood serum of glaucoma patients as a measure of ocular health: A Raman spectroscopic study

Abstract

Carotenoids are a major component of the human diet and have been widely studied for their antioxidant, and vision protection roles in the human body, and dietary supplementation is promoted in particular for ocular health. An initial trial (European Nutrition in Glaucoma Management (ENIGMA)), which assessed macular pigment optical density (MPOD) as well as ocular structural, functional and perceptual parameters before and after the 18-month supplementation of glaucoma patients with macular pigment (MP) carotenoids (lutein, zeaxanthin, meso-zeaxanthin), confirmed supplementation significantly improved the clinical ocular health of participants. Blood contains all major dietary carotenoids, presenting it as a suitable and efficient alternative medium for analysing dietary carotenoids in vivo. Raman spectroscopy, a proven efficient analytical tool was used to explore the impact of the supplementation on participants’ serum carotenoid levels and any correlations with MPOD and other ocular responses. Samples obtained from the pre-supplementation baseline and 18-month supplemented participants were analysed. An inverse relationship was observed between percentage change in Raman intensity over the supplementation period and the baseline Raman serum measurements, indicating greater relative benefit of carotenoid supplementation for people with low MPOD/serum carotenoids pre-supplementation. Partial least squares regression (PLSR) was employed to analyse the spectra after pre-processing and the loadings reflected the carotenoid content and structural profile. MPOD results correlated at all eccentricities, with a coefficient of determination (R2) of 0.62 – 0.92 and % Root mean squared error <44%. Structural, functional and perceptual parameters analysed also showed good degree of correlation with the serum Raman measurements. The results support the conclusions of the ENIGMA trial and suggests strategies for optimising patient responses to supplementation, based on baseline carotenoid levels, and furthermore points to the significant potential of Raman spectroscopy of serum carotenoids as a simple and reliable alternative method for investigating macular pigment carotenoids and assessment of patient health.