Hi and welcome!
I will answer the questions that I can, or try to.
1. If I read correctly, the time frame is either 7 months of age, or 12 months of age? If you're talking a difference of 5 months, I would be comfortable with the decision to defer. I do know of patients with SWS who did not develop either glaucoma or experience seizures until adulthood. If you really feel that you can get a more conclusive result at one year of age, I think you should do that. *That's an opinion... as a parent, I would be comfortable with that.
2. I do know of families that we've helped that have pws in that region with no SWS indicated. If no one posts here in the next couple of days, I'll see if I can track someone down for you.
3. Make sure you always, always, always continue with regular eye exams to check for glaucoma.
4. I have no idea about costs in the UK.
As things progress, if you have more questions of a detailed nature, try to write to Dr. Anne Comi. You can reach her via:
She is usually very prompt with answers.
And, try not to worry, Mum. I know it's hard not to worry ... that's what mothers are programmed to do! But take a deep breath and go play!
That age is so fun, especially when they are all smiley!