Glaucoma, an optic neuropathy characterised by progressive neurodegeneration of the inner retina, remains the leading cause of irreversible vision loss and, as the population ages, integrative strategies to prevent or delay its onset are being considered.
Although the etiopathogenesis of the disease is not fully understood, there is a growing consensus that mitochondrial dysfunction and redox imbalance are involved in the elevation of intraocular pressure and the initiation of retinal neurodegeneration.
Furthermore, given the importance of macular pigment for optimal visual performance and retinal health, the neuroprotective association between macular carotenoid levels and glaucomatous neurodegeneration is of particular relevance. In light of both of these evidences, therefore, there is a plausible rationale for the use of carotenoid supplements to support glaucoma management. From the available evidence, it appears that the glaucomatous retina creates a hostile environment for neuronal survival, in part due to sustained oxidative injury with a concomitant depletion of endogenous antioxidant defences. The effect of glaucoma appears to compromise the availability of lutein, zeaxanthin and meso-zeaxanthin, contributing to deteriorating retinal health.
In the aqueous humour of patients with primary open-angle glaucoma, data consistently show a significant reduction in total antioxidant capacity compared to age-matched healthy controls. Data from a meta-analysis and cross-sectional studies confirm these findings, providing consistent evidence of a systemic imbalance between oxidative stress and antioxidant levels in various types of glaucomatous lesions. To date, a number of epidemiological studies have evaluated the relationship between dietary carotenoid consumption and glaucoma incidence, but the results are largely inconsistent.
Despite this, evidence from several small study groups seems to confirm a protective association with higher consumption of food groups rich in carotenoid content. A recent cross-sectional analysis of a cohort of African-American women included in an osteoporosis study found a more significant protective trend against glaucoma among those who consumed more vegetables with high carotenoid values on a weekly basis. It should be noted that none of the epidemiological studies directly assessed the association between serum carotenoid levels and glaucoma risk.
Prospective studies of glaucoma patients evaluating the efficacy of carotenoid supplementation with antioxidant micronutrient formulas in randomised controlled trials remain limited. In a long-term open-label follow-up among patients with mild/moderate glaucoma, two experimental antioxidant formulas containing lutein (6 mg) and zeaxanthin (0.3-0.5 mg), with or without omega-3 fatty acids, showed no significant changes after a two-year follow-up on visual field loss or specific quantitative measures.
In contrast, a prospective study with an antioxidant nutraceutical formula containing lutein (10 mg) and zeaxanthin (2 mg) in glaucoma patients and healthy controls showed a significant protective trend with carotenoid supplementation after a six-month follow-up. In the group with the disease, a marked increase in plasma antioxidant capacity and a concomitant reduction in pro-oxidant stressor or malondialdehyde was observed.Similar protective trends were also observed in patients with pseudoexfoliative glaucoma in clinical trials with a carotenoid supplement.
Based on the preliminary results available, carotenoid therapy has shown neuroprotective benefits, but it remains to be seen whether this additional nutraceutical approach, in combination with pharmacological therapy for ocular hypertension, can provide additional protective benefits to glaucomatous eyes.
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Supplementation with docosahexaenoic acid (Dha) plus antioxidants in pseudoexfoliative glaucoma: a 6-Month open-label randomized trial. J. Ophthalmol. 2018, 2018, 8259371.
Effect of an oral supplementation with a formula containing R-lipoic acid in glaucoma patients. Arch. Soc. Esp. Oftalmol. 2020, 95, 120–129.
Chapter 6—Oxidative stress and mitochondrial failure in the pathogenesis of glaucoma neurodegeneration. In progress in brain research 2015; Volume 220, pp. 127–153.
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