Courtesy of Dan Cooper from the Facebook Trilobites group, a rare Isotelus eye with lenses preserved.  The claim for this specimen is ~1000 eye lenses, but with all due respect, much closer to ~5000 lenses.   Do the math!         table from:   Rose, J.N. (1968) The eyes of Isotelus and Nileus. Proceedings of the Iowa Academy of Science, 74:178-185