Hi @colewd, @Mung and @swamidass,
Some years ago, I wrote an article on Uncommon Descent that was a take-down of Nilsson and Pelger’s 1994 paper on the evolution of the eye. Here it is:
Did the eye really evolve in a geological blink?
In 2013, however, Nilsson authored a much better paper, titled, Eye evolution and its functional basis, which traced the evolution of opsins over time, and which contained a detailed model of how the eye evolved in all animal phyla.
Here’s another paper, by Ramirez et al., which I think might also interest you, as it’s recent (2016) and it deals with opsin evolution:
The Last Common Ancestor of Most Bilaterian Animals Possessed at Least Nine Opsins
Cheers.