When eyes are a problem
Sometimes, evolution can take it back. Many cave dwelling animals have lost their eyes. Theories as to why this happen range from genetic drift, to mutations that improve other senses interfering with the proper development of eyes, to the energy cost of growing and maintaining vision. I suspect that it has to do with how easily injured eyes are when they don’t work. I’ve never seen that brought up by scientists; maybe you have to go blind to get it.
Here’s an article on the kiwi bird and how it may be losing its sight as a species. Special thanks to @seeingwithsound for the article and pointing me to this topic.
Here’s an article on changes in the brains of sightless animals.
Here’s a paper on animals that have given up eyes, and how and why they may have done so.
Here’s an article on blind cave fish that includes a video.
And an article on how the offspring of blind cave fish can regain their sight.