Coloboma is often associated with cardiac disorders.

[G-Unit]

Here's a non family member who seemed to know all about that eye. She knew them from the nursery in Amsterdam.

14th May 2007
Seija Rutter: "Yeah, the pupil runs into the iris and that's something that she'll always have and that will never, ever change and I think this is positive, this is something that's completely unique to Madeleine and she's instantly recognisable from her eyes."
https://www.gerrymccannsblogs.co.uk/Nigel/id52.htm