This is responsible for the development of the slowly progressing visual changes, usually over 20 to 60 minutes. These migraines are also known as scintillating scotomas.
In retinal migraines, the visual symptoms take place in the retina rather than across the outer brain cortex. They occur in only one eye, before or during the headache phase. The disturbance in retinal migraine may also result from abnormal spreading of electrical activity, except it occurs in the retina. The disturbance may also be due to reduced retinal blood flow.