OK,at the risk of being sent to Pedants corner, if you are getting visual aura (zig zaggy arcs in vision, then this is happening in the visual cortex part of the brain, and you'll see it in both eyes, eyes open or closed. No way should the GP be sending you to an optician for this. Losing sight over some part of vision on one eye, which then comes back might be retinal migraine. An optician may be able to see this looking at the back of the eye, but only when its happening. I don't know what ocular migraines are; I've seen the term used for both aura (in the brain) and retinal migraines. Probably better to avoid the term.
Anyway. What do I know. Like you my migraines only come as visual auras, they last about 20 minutes, but I feel flattened for a day afterwards, although there's no headache. I was taking propanolol which controlled the migraine well, but out of the blue I suddenly went from 3 or 4 a year to 20 in three months (and three in one day), so I'm now on Topiramate (after a fairly urgent scan - nothing found), and I've had only one this year.
Sorry - rambled! Bottom line, there are medications, but migraines are common so unless you have a lot or increased frequency it won't be seen as urgent, but if you do see the GP don't be fobbed off with talk of opticians!
HTH