Geez, more than a few of us experiencing these then. They started for me around 3 years ago, all post ride so I put them down to dehydration or fatigue. Not too often, every few months or so. Then I had one earlier this year but not after a ride- not dehydrated, tired or stressed so I panicked. Off to GP, had an eye test straight away, MRI a few weeks later that was all clear. The optician advised that it was a migraine type visual disturbance, as long as it didn’t last longer than 30 minutes or happen increasingly often, not to worry.