In a rare find, it was possible to distinguish cellular structures in the eye:
Schoenemann and her co-author Euan Clarkson of the University of Edinburgh in Scotland published their analysis of the ancient eye on Thursday in Scientific Reports. Despite being 429 million years old, the trilobite has a modern-looking eye that resembles those of today’s bees and dragonflies. This type is called an apposition compound eye, meaning each lens acts independently to create a mosaic image of what a creature sees.
The detailed look at the trilobite’s eye helps track the evolution of eyes and vision in arthropods over time, says University of New England paleontologist John Paterson, who was not involved in the new study. “The take-home message appears to be that trilobites had developed apposition compound eyes during the earliest evolutionary stages of the group and stuck with this design throughout their history.” Riley Black, “Rare, cracked fossil shows the world through ancient eyes” at Scientific American
Paper. (open access)
Note that we are told that the find “helps track the evolution of eyes and vision in arthropods over time” but in this case, it appears that their wasn’t much evolution: They “developed apposition compound eyes during the earliest evolutionary stages of the group and stuck with this design throughout their history.” No matter the history, Darwin must be placated.
See also: Stasis: Life goes on but evolution does not happen