Hi Nick
Oh crikey, you must really feel like you drew the short straw sometimes -- no vision in one eye due to one thing, then you get Keratoconus in the other eye. I swear, I'll never compain again... Okay, won't complain quite as often
Right, the "decision tree" for electing for crosslinking is usually as follows:
1) Unequivocal diagnosis of Keratoconus -- you have to be sure that it is Keratoconus (usually easy but not always). In your case that's a "check" though, so we can move to the next stage
2) Conclusive evidence that Keratoconus is actively progressing. The only thing that crosslinking brings to the party is to (hopefully) halt progression. Some patients have reported visual improvements, some have lost a line or two on the Snellen chart, some are neutral. So there's no point in opting for crosslinking with the intention of improving vision. It's nice if it happens but that's not a guaranteed outcome. Sometimes you're left worse off.
3) A rate of progression which both the ophthalmologist and the patient considers to be a cause for concern. Here is where it might be tricky because ideally you'd want two reference points 6 months (minimum) to 12 months (ideally) apart. The snag is, if you've not got this information you have to wait for the time to elapse to get it. But with luck, whoever is looking after you in the clinic you attend already has this information. What you'd need to think about is what progression, if any, is too much for you to gamble on.
4) A suitably thick cornea. Indications are still evolving as to just how thin your cornea can be before crosslinking is too risky. Figures I've seen are in the range of 350 microns but that might not represent current clinical thinking. And that is for "eip-off". It might well be different for "epi-on". Really best to discuss this with the ophthalmologist after they've got some test results. For you in your unusual situation, your risk tolerance may well be less. For example, let's say you're 350 microns which the consultant says is at the lower boundary for what they'd normally consider, with anything less being a contra-indication. If you had two working eyes, then you might think that taking everything in to account, it isn't an issue. But you don't, so a marginal eligibility for crosslinking might be too close for comfort for you. Definitely, then, go through this aspect with the consultant (if you go as far down the line as that).
As I said, you've really got my sympathy here. I don't envy having to make the sort of choices you might have to make. In many ways, sometimes more choice (i.e. new treatments becoming available) are a mixed blessing. Yes, you've got some options which you didn't have before. But never, in my experience with Keratoconus, has any clinician said to me "Chris, you absolutely have to do X- or Y-". It's always "Well, you could do this... or you could do that... or you could do nothing..." with a risk/reward trade-off that ultimately we have to sort out for ourselves. Hopefully the points I've given above will give you some idea of the constraints around crosslinking that you need to work out if they apply to you. Could be that it's simply not a viable option for you anyway. If it is though, by working through the above, you'll be able to figure out whether it is the right solution.
Ask away if there's anything you'd like to know that I've not covered.
Best wishes
Chris