Studies on the eyes of bigeyes (Teleostei Priacanthidae) with special reference to the tapetum lucidum

Abstract

Abstract Eyes of glasseyes (Priacanthidae) show conspicuous eyeshine and have a brilliant tapetum in the chorioid. The tapetum underlies the entire retina; it is composed of several rows of reflecting cells which contain stacks of flat crystals lying parallel to the retinal surface in the central fundus and obliquely towards the periphery. Reflexion is orange and specular; the reflexion spectrum is a broad band centred at about 630 nm. Processes of the pigment epithelium contain black pigment in some parts of the eye; pigment is especially dense in a horizontal central band and in the lower field, but is absent from the cell bases. The ultrastructure of the pigment epithelium and of the tapetum is described. The crystals and intervening cytoplasmic lamellae are organized as quarter-wavelength films to give maximal reflexion of long wavelengths (orange and red light) by constructive interference. Rods and cones are present; there is no retinomotor activity. The mechanism of reflexion, efficiency of the tapetum and role of the retinal pigment are discussed.