@Jem - Interesting feedback. In your consultation, were you given an indication of the level of improvement that a further operation might offer? Because that should also be a factor in your consideration.
If he can offer a significant and lasting level of improvement, that might mean it is an operation worth having, although a 1 in 2 chance of any improvement is not great. If they can not offer a significant level of improvement, then it would sway the odds still further against having a further procedure.
I would also want to know the risk if any of deterioration in your vision as a consequence of the procedure before I made a decision....