Hmm... Just ran across your post. I missed it before somehow.
Bella has a similar crescent. I've brought her to the vets and had them look at it (yes, plural vets). They weren't particularly concerned, noted that it happens from time to time. One suggested we could try an eye drop, though it probably wouldn't either help or hurt. We did go with an antibiotic eye drop for a little bit just to see -- and it didn't really change anything up.
So, now, she just has this little wedge there. Doesn't seem to bother her at all. I, of course, worry that it's a sign of something larger that's gone undetected by the vets. But, as it hasn't really changed much over time, it doesn't seem to bother her, and the vets are disinclined to believe it's a bad thing, I'm just monitoring it.
How's it going for Mia?