Chitinous extracellular laminar secretion that covers each ommatidia of the adult eye. It is optically clear and biconvex, being around 5um thick at its center, and it covers the pseudocone layer. It is secreted by the underlying four cone cells and two primary pigment cells. The cornea between the facets is secreted by the secondary and tertiary pigment cells and although continuous with the lens, it is not stacked in deep layers.