First signs of glaucoma injury occur in the brain.  What has generally been considered an eye disease is actually related to conditions such as Alzheimer's and Parkinson's diseases.
D000544:Alzheimer Disease / Q000473:pathology; D001921:Brain / Q000473:pathology*; D002450:Cell Communication / Q000502:physiology; D005901:Glaucoma / Q000473:pathology*; D006801:Humans; D009410:Nerve Degeneration / Q000473:pathology*; D009900:Optic Nerve / Q000473:pathology*; D010300:Parkinson Disease / Q000473:pathology; D012307:Risk Factors