Inhomogeneous Refractive Index in the Crystalline Cone of a Moth Eye

Abstract

FROM investigations of arthropod compound eyes, Exner concluded that a dioptric effect in each ommatidium was due not only to the curved surfaces of the corneal facet and the cone tip, but also to a specific decrease of refractive index from the axis to the periphery of the dioptric apparatus^1,2. He called this refractive system a lens cylinder and assumed it to be present particularly in the dioptric systems of eyes which form superposition images. The first evidence of lens cylinder properties was presented for the cornea of the beetle Hydrophilus¹ and recent interference measurements have also demonstrated such properties in the pseudocone of the firefly eye³.