Fine structure of the tapetum lucidum of the domestic ferret

Abstract

The fine structure of the tapetum lucidum of the domestic ferret was studied by both light and electron microscopy. In this species the reflective layer is a tapetum cellulosum situated in the choroid and restricted to the superior fundus. Posteriorly in its thickest region, the tapetum is composed of 10–12 layers of flattened polygonal cells. The number of layers gradually decreases peripherally and eventually the tapetum disappears. The nucleus of the tapetal cell is usually centrally located. Small mitochondria are scattered peripherally while the few other cell organelles observed are normally clustered near the nucleus. The dominant cytological feature of these cells is numerous electron dense rodlets whose long axes are perpendicular to the oncoming light. These rodlets are the reflective material of the tapetum. The orientation of these rodlets is normally uniform within each tapetal cell but may vary between adjacent cells. The diameter and spacing of these rodlets are consistent with the principles of constructive interference. Blood vessels penetrate the tapetal layer at right angles to supply the choriocapillaris. The choriocapillaris is indented into the retinal epithelial layer to give a flat reflecting surface to the tapetum.