Glaucoma, characterised by cupping of the optic nerve head and irreversible loss of retinal ganglion cells, affects roughly 70 million people worldwide and is the leading cause of irreversible blindness. But glaucoma is often asymptomatic for an extended time period, and therefore fewer than 50% of affected subjects are aware of their disease. Diagnostic markers are urgently needed and in March Nature Medicine, researchers at Tufts University School of Medicine, Boston, report the finding of the first such marker.