Sorry you've had no response to this post Mauro as I was hoping someone may have an answer, as corneal ulcer's isn't something I've heard of caused by CPAP. However, we do often warn of why it's important to ensure the masks aren't leaking into the eyes because that's not good for them at all!
There several eye conditions linked with sleep apnoea itself though, and this is a good link I've shared often about this https://www.aao.org/eyenet/article/obstructive-sleep-apnea-eye-opht... It's yet another reason why it's important for people to be treated for their sleep apnoea. I used to suffer from Floppy Eye Syndrome before I was diagnosed and research has even stated 100% of people with this also have sleep apnoea. My eyes are much healthier since I've been on CPAP, apart from age catching up with me now!
If you haven't tried mask liners then that would be worth doing as they help lots of people with mask leaks http://www.hope2sleep.co.uk/silent-night-mask-liners.html Many people also find they can loosen the mask straps slightly whilst using them. Perhaps your clinic could help too with trying you with a different mask to minimise the mask leaks.
I hope things are improving since you posted.