TLR4 and glaucoma: Importantly, clinical studies have linked primary open-angle glaucoma to specific mitochondrial cytochrome c oxidase subunit I of the oxidative phosphorylation (OXPHOS) complex IV [8] and single-nucleotide polymorphisms of toll-like receptor 4 (TLR4) [9]; this suggests a connection between OXPHOS stress-induced mitochondrial dysfunction and TLR4-mediated neuroinflammation in glaucoma neurodegeneration.