weird visual disturbance

[meddie]

Just had a really strange episode. looking at screen and noticed what looked like a bit of water was on my glasses in the centre of my vision, there was nothing on the glasses, this blurry patch then gradually enlarged over the following 15 minutes spreading out towards the edge of my vision and clearing up in the middle as it went. it was like a pulsating wiggly lined ring gradually getting bigger. Its now gone anyone got any ideas what it was?

I've had this three times in my life. First time 12 years ago, second time a month later, third time 8 years after that. Nothing since. No headaches, no other symptoms ever. The weirdest thing about it is how randomly spaced the three "attacks" were!