Trilobite eyes: An impressive feat of early evolution — Science News, February 2, 1974
[Trilobites] possessed the most sophisticated eye lenses ever produced…. The lens structure does not correspond to any found in modern arthropods, as it developed when trilobites were already a separate stock and doomed to extinction…. Though the trilobites were lavished by nature with this great optical gift, there is no way to know whether the trilobites made full use of it.
Update
With some 20,000 known species, trilobites were a diverse bunch that went extinct about 250 million years ago. The lenses described in 1974, found in trilobites called phacopids, are similar in shape to some telescope lenses. That suggests phacopids could focus on objects near and far in their field of view. Recently, a fossil analysis has found that the creatures’ optical gift was even more spectacular than scientists thought. Phacopids appear to have had two compound eyes, like those of flies and other insects. But each eye contained up to 200 smaller peepers, which would have helped the trilobites detect light in dark ocean waters, researchers reported in 2021.