Studies on the eyes of toadfishes Opsanus. Structure and reflectivity of the stratum argenteum

The light-adapted eye of the toadfish (Opsanus, Batrachoididae) exhibits eyeshine. The chorioid is yellow and has a yellow stratum argenteum. This is a bilaminate tissue, consisting of an inner iridescent sheet containing pentagonal crystals, and an outer sheet containing birefringent yellow granules. There is no melanocyte layer in the chorioid. In the photopic eye the retinal pigment migrates into the cell processes and surrounds the cone outer segments. Spaces between the cones and processes are pigment free, and part of the light incident upon the retina is transmitted through it to the argenteum and reflected by the latter into the retina. The pertinent tissues are illustrated, and spectrum curves for transmission and reflection are presented.