Note
Peripheral mitochondria give off tubular elements in the calycal processes. Pigment epithelial cells have long processes which extend vitread to the cone ellipsoids and contain tapetal spheres (0.3 to 0.5 μm). The processes form a diffusely reflecting tapetum about 80 μm thick. In the scotopic eye the tapetum is uncovered when the retinal pigment retreats into the cell bases. The reflecting material is a triglyceride, largely glyceryl tridocosahexaenoate. Its high refractive index (n = 1.50) and the close packing of the spheres cause light to be backscattered. Reflection from the white lipid tapeta is about 50%; quantal catch in the retina because of the tapetum is enhanced by a factor of about 1.5.