Then you haven’t read what you’ve linked. Go back and read it and then I’ll reply further.
Pax 6 is a master control gene for eye morphogenesis; sequence comparisons have shown that evolution has recruited crystallins among already existing heat-shock proteins and stress-inducible enzymes,
or the use of existing proteins in the development of new structures;
The genetic control of eye development and its implications for the evolution of the various eye-types,
pretty stright forward;
The finding of Pax-6 from flatworms to humans suggests that eyeless is a universal master control gene and that the various types of eyes in the various animal phyla may have evolved from a single prototype... The wide variety of eyes in the animal kingdom may, therefore, have evolved from a single ancestral photosensitive organ...
Common descent? Ruh roh!;
Hmmm... Is this your "money shot"?
The evolutionary mechanisms responsible for eye degeneration in cave-adapted animals have not been resolved... (But) the manner of eye development and degeneration, the ability to experimentally restore eyes, gene expression patterns, and comparisons between different cavefish populations all provide important clues for understanding the evolutionary forces responsible for eye degeneration. A key discovery is that Hedgehog midline signaling is expanded and inhibits eye formation by inducing lens apoptosis in cavefish embryos. Accordingly, eyes could have been lost by default as a consequence of natural selection for constructive traits, such as feeding structures, which are positively regulated by Hh signaling. We conclude from these studies that eye degeneration in cavefish may be caused by adaptive evolution and pleiotropy.
Pleiotrophy is where a mutation in a single gene can influence multiple phenotypic traits - in other words, it is not a question of gain or loss, the eye morphology is a product of adaptation and selection of a beneficial mutation.