An ocular migraine (also called retinal migraine)  is a rare health condition marked by temporary vision loss or temporary blindness that affects one eye . The vision loss typically lasts less than one hour. Vision loss from ocular migraines starts as a small blind spot  in the central vision of one eye that gradually expands until it crowds the visual field.
An ocular migraine can be painless. It can also occur before, following, or along with a headache. Headaches caused by ocular migraines typically affect only one side of the head. Ocular migraine headaches can be moderate or quite debilitating. They usually last between four and 72 hours.
This type of migraine is believed to result from reduced blood flow or blood vessel spasms in the retina of the eye. Some believe the condition is linked  to changes in the retinal nerve cells. The precise cause of ocular migraines is not known, but it is thought to have the same causes as regular migraines.
This article discusses some of the possible causes and triggers of ocular migraines.