My eyes use to get red frequently sometimes right and other time left eye . The eye which gets red that side I use to have severe half head ache for 4 to 5 days. Consulted neuro and potho all test were done like MRI but everything thing normal . Neuro specialist daignosed and said it's cluster head ache . Since I work in saudi arabia I don't know whats the reason of repeated problem of red eye and head ache