Get it checked out, for sure.
I've had something similar to this, for thirty years now. I first noticed it only when my eyes turned to the side a long way, and I noticed it more when the light was dim. It looked like a jagged streak of lightning, and there was also a flash of pain with it. A few times back then things in my eyes were suddenly a lot more sensitive, I didn't have to turn my eyes very far to get this effect and the pain was much worse. Eye pain, not headache pain, although I did get a stab of headache at times too, only when I saw the flash. I had photophobia too, but as I said - only when the problem was suddenly a lot worse.
I got it checked out, they clearly were thinking "detached retina" but it wasn't. I remembered something my mother had told me about her sister (who died of appendicitis in her early 20s, WWII). Apparently my aunt had been told that the muscles behind her eyes were hardening and she would eventually go blind. Nobody has ever been able to work out what she REALLY was told; that didn't seem to make sense.
Anyway, the problem has continued and slowly become more noticeable (I can't say 'worse' because it's not a handicap). And now - I don't see a lightning flash, I see a full circle. With either eye (sometimes both) and I don't have to turn my eyes very far at all.
I get my eyes checked regularly, but all the really intense checking I had done over the years, I've never been given an official answer from a specialist. Yes, I've had 'migraine' suggested, but this isn't associated with the really nasty headaches I sometimes get. This is different.
What we've worked out this probably is - the muscles of the eye, the ones on the outside responsible for moving the eyeball this way or that. They pull on the eyeball which pulls on the retina. Being short-sighted, my eyeball is longer than it should be. Over the years my eyes have become worse (with myopia) and hence, my eyeball has lengthened. This means that as my eyeball turns, the forces on it are uneven and the muscles pull on the vitreous humor, which then pulls on the lens muscles inside the eye and especially on the attachment points for the lens (hence the full circle - the forces inside the eye are now much more evenly spread over the entire circle of the lens attachment).
It's not serious, but if the pull gets really bad, the retina can detach. It can also pull on small blood vessels, causing them to leak. This can cause vision problems. At the very least, it can cause an increase in 'floaters'.
With all those possibilities, it therefore does need not only to be checked out but also monitored regularly.
A big giveaway to this being the likely explanation - the lightning flash or the circle - it's only white. No colour. Our eyes have four different types of light detectors in them, located in the retina. The closer together the detector cells, the more fine detail we can see. Birds' retinas are much more crowded than ours, that's why an eagle can see its prey from an incredibly high distance. The main detectors, the rods, only detect light/dark but they are VERY sensitive. Almost the entire inner surface of the eyeball has rods, although where they are well away from our central vision, they are more sparse. As we get closer to our central vision, we get the cells which detect colour - the cones. There are three different kinds, each kind will detect a different colour. One kind detects red, another kind detects green, and a third detects something in the blue range. And on TV tonight I saw a program which said bulls have two kinds of colour detectors (as well as the rods). Cones also cut out their detection at a higher light level. That's why as it gets dark, we lose colour in the environment.
In the very centre of the retina, corresponding to the point where we see most detail, is a small pit. In this pit are only cones, no rods. And what's more, the nuclei of those cones have all been pushed to one side, so our retinas can get maximum detection capability without parts of the cells getting in the way. That's why the pit is there.
It's called the fovea, or sometimes the macula densa. So when you hear of someone having macular degeneration, what is happening is they're losing their vision beginning with this central bit going first. Not nice. A friend of mine has this, she can only see via her peripheral vision. The maddening thing is, your instincts make you turn your eye to look at what you want to see, but in her case that swings the area of non-vision there and she loses the image.
The other weird thing about eyes and our vision - the Blind Spot. It's the gap in our retina where allowance has had to be made for the optic nerve, which is like the main cable connecting the retina to the brain. It has to go SOMEWHERE, and where the cable is, there are no detector cells. But the brain is tricky - we don't see the blind spot as a gap in our vision, our brain 'bleeps over it' and fudges in what it THINKS should be there.
The brain does the same trick when you begin losing vision for any of a number of reasons. As a result you might think your vision is perfectly OK, but it's not. You could be gradually going blind but your brain is hiding the fact, until you begin tripping over things you could have sworn were not there...
So my recommendation - get this checked out, and get an optometrist or ophthalmologist to keep monitoring it. It COULD be migraine prodrome, but if you are more short-sighted than most, chances are it could be the problem I describe. For reference - my glasses prescription is -5 to -5.5 diopters. If yours is anything more than -4, this could be a possibility for you.
For now - I see perfectly OK, as long as I have my glasses on!
Marg