https://phys.org/news/2018-05-eye-loss-cavefish.html

A. mexicanus is a tropical freshwater fish native to Mexico. A few million years ago, some of these fish presumably got trapped in dark caves and gave rise to completely different varieties, or "morphs," that lack eyes and have several other unique physical, behavioral and physiological changes. Despite their dramatic differences, surface and cave morphs share similar genomes and can interbreed. Cave morphs begin eye development early but fail to maintain this program, undergoing eye degeneration within a few days of development. Previous research has not revealed any obvious mutations in genes important for their eye development.

The new study, conducted by researchers at NICHD and the University of Maryland, College Park, shows that epigenetic-based silencing of a large set of genes limits the eye development of cave-dwelling A. mexicanus fish. Twenty-six of these genes are also expressed in human eyes, and nineteen are linked to human eye disorders.