Conserved optical adaptations enable amphibious vision in compound eyes

The visual systems of amphibious animals must perform in two optically
distinct environments: air and water. Little is known about how
diffraction-limited, arthropod compound eyes maintain optical function
across the air-water interface, aside from one commonality: flat corneas.
Since the external shape of a lens is only one of several properties that
influence optical performance, we examined how compound eye corneal optics
varied with amphibious ecology across two biological transects:
developmentally in one insect species and comparatively among multiple
species. Both analyses revealed that flat corneas alone are insufficient
to provide amphibious optical performance. Compound eye corneas
universally combine flat external surfaces, rounded internal surfaces, and
inwardly expanded thicknesses to support visually-guided behaviors in air
and water. Conservation of these features among diverse groups provides a
strong evolutionary link between the optical performance of compound eyes
and the environmental medium.