I am repeating this post in the hope of more replies....
I haven't met or come across others (apart from DorsetLady) who've lost sight through GCA, and would be interested to know of different experiences of sight loss.
My first sign of GCA was jaw claudication, 10 months after being diagnosed with PMR, when my Pred dose was down to 6. The GP shot me up to 60 immediately, nasty shock but she said we must save your sight. I had a biopsy confirming GCA, but no headaches or visual symptoms. One Wednesday evening six months later (this excited the rheumatologists as the time lapse between diagnosis and sight loss was unusual), Pred now down to 9, I noticed a small dark mark on the upper vision of my right eye - no other symptoms - and went straight to my local A&E. It was the first day of the junior doctor strike (although that may not have been a factor) and the young man who looked down the machine gave me a tube of cream for a scratch on my cornea. I saw my GP and the Eye Unit during the next two days but in the end made an appointment with an optician, who took a photo of the back of my eye which showed a haemorrhage in my optic nerve. After that it was St George's, the closest out-of-hours eye emergency (Saturday by now), and was there 11 hours. Basically there was no treatment other than high doses of pred... I saw a private consultant a few days later, who confirmed I'd had an AION (anterior ischaemic optic neuropathy), basically a stroke in the optic nerve. He was so grave about it I finally understood I would be permanently virtually blind in that eye.