Summary
Glaucoma is the leading cause of irreversible blindness in the world. The disease is characterized by excessive fluid accumulation in the eyes that damages the retina and optical nerve, often accompanied by decreased antioxidative capacity and inflammation. This results in visual impairments, eventually leading to blindness. Research has established a link between insufficient DHA levels and glaucoma prevalence. Studies employing DHA supplementation report a positive effect on glaucoma pathology reduction.

Introduction
Glaucoma accounts for the majority of irreversible blindness cases worldwide and can be divided into two main categories: open-angle glaucoma and angle-closure glaucoma. Several sub-forms of these categories exist, such as pseudo-exfoliative glaucoma. In all instances of glaucoma, a disbalance arises between fluid production and drainage in the eyes, leading to alterations in fluid pressure in the eyes. The pressure of fluid in the eyes is called intraocular pressure (IOP). When this becomes excessive, the retina and optical nerve are squeezed and become damaged. Conversely, the main treatment for glaucoma is focused on reducing the IOP, though not all patients experience a decrease of symptoms in response to this treatment. Additional pathological conditions often accompanying elevated IOP in glaucoma are decreased antioxidant capacity that leads to oxidative stress and inflammation. This has lead researchers to investigate the role of omega-3 polyunsaturated fatty acids in the context of glaucoma, due to their anti-inflammatory and antioxidative properties.

Research findings
To determine the effects of omega-3 fatty acids EPA and DHA on glaucoma risk and prevalence, researchers from the University of California Los Angeles assessed the dietary omega-3 intake of 3865 individuals aged 40 or above (Wang et al., 2018). Their analysis showed that low EPA and DHA intake is associated with glaucoma. They went on to conclude that daily dietary intake of DHA was protective towards glaucoma risk.

In a study by researchers from the university of Melbourne, the effects of omega-3 supplementation on IOP were investigated in adults without elevated IOP based on the pooled data of 2 publications (Downie & Vingrys, 2018). Four supplementation conditions with ( and one placebo conditions were included. During a daily supplementation period of three months, 72 individuals received omega-3 fatty acids (∼1000 mg EPA+ ∼500mg DHA ± 900 mg ALA) and 33 individuals received a placebo (olive oil). The controls showed a minor increase in IOP after three months, whereas the supplementation group showed a robust decrease in IOP.

A 6-month DHA supplementation trial was conducted by Villadóniga and colleagues to assess the antioxidant effects of DHA in the context of a sub-form of open angle glaucoma called pseudoexfoliative glaucoma (Romeo Villadóniga et al., 2018). Men and women aged 18-70 with initial or moderate pseudoexfoliative glaucoma were given either a daily placebo (olive oil, 24 individuals) or daily supplementation containing 1050mg DHA as main component (23 individuals). After 6 months, the supplementation caused a decrease in IOP, whereas the control group did not differ in IOP compared to the start of the study. Next to a decrease in IOP, the supplementation group showed a decrease in plasma inflammatory markers, oxidative stress markers and improved antioxidant capacity. On this basis, the authors concluded that DHA is protective against pathology of pseudoexfoliative glaucoma.

Conclusion
Multiple studies have highlighted the role of omega-3 fatty acids in glaucoma. A large population study established the inverse association with dietary DHA and EPA intake and glaucoma risk. In agreement with this,  supplementation with omega-3 fatty acids has shown to decrease the intraocular pressure (IOP) in persons without glaucoma. This is relevant as all types of glaucoma are characterized by excessive IOP. Furthermore, in persons with a pseudoexfoliative glaucoma, supplementation containing high-dose DHA as well as minerals and vitamins causes a decrease in disease pathology markers. Overall, these findings indicate that DHA plays a positive role in the prevention and reduction of glaucoma pathology.

References
Downie, L. E., & Vingrys, A. J. (2018). Oral Omega-3 Supplementation Lowers Intraocular Pressure in Normotensive Adults. Translational Vision Science & Technology, 7(3), 1. https://doi.org/10.1167/tvst.7.3.1

Romeo Villadóniga, S., Rodríguez García, E., Sagastagoia Epelde, O., Álvarez Díaz, M. D., & Domingo Pedrol, J. C. (2018). Effects of Oral Supplementation with Docosahexaenoic Acid (DHA) plus Antioxidants in Pseudoexfoliative Glaucoma: A 6-Month Open-Label Randomized Trial. Journal of Ophthalmology, 2018, 8259371. https://doi.org/10.1155/2018/8259371

Wang, Y. E., Tseng, V. L., Yu, F., Caprioli, J., & Coleman, A. L. (2018). Association of Dietary Fatty Acid Intake With Glaucoma in the United States. JAMA Ophthalmology, 136(2), 141–147.                                                                                    https://doi.org/10.1001/jamaophthalmol.2017.5702