Through careful genetic analysis, scientists isolated the genetic change, a mutation to the gene cystathionine beta-synthase a, or cbsa. The mutation cuts off blood flow to the eyes of the blind cave fish during embryonic development.

"We know that genes controlling eye degeneration are scattered all over the Mexican cave fish genome," study co-author William Jeffery, a professor of biology at the University of Maryland, said in a news release. "There may be 10 to 20 different genes involved, and this is the first time we've been able to pin down one specific gene and show the mechanism at work."

Researchers began by selecting a handful of genome regions that might host the mutations responsible for eye degeneration. Scientists observed changes in these regions during the period of embryonic development when cave fish lose their eyesight.

The research showed mutations to the cbsa gene were present during the embryonic development of all blind Mexican cave fish, but absent among Mexican tetras with eyesight.