How to get the comment/post description of a Photo in a shared Album?

Hi I want to show a shared photo album in my app. Using PHPhotoLibrary.shared() and PHAssetCollection I get all photos of the requested photo album and I get an information if the album content changes. So far so good, but i want to access the comments on the photos and the post text , which can be added when adding photos to a shared album. Is there anyone who has a solution for this problem? regards Sven