In addition, other circulating biomarkers associated with neurotrophy, neuroprotection and oxidative stress have been found altered in glaucoma, including serum homocysteine, vitamin B12, folic acid and endothelin-1 (ET-1; Cumurcu et al., 2006; Turgut et al., 2010; Türkcü et al., 2013; López-Riquelme et al., 2015). This evidence concerns the gene EDN1 and glaucoma.