Light and electron microscopic studies on the pigmented epithelium and photoreceptors of the retina of common buzzard (Buteo buteo)

The current study is essentially carried out to reveal the histological and ultra-structural details of the retinal pigmented epithelium (RPE) and photoreceptors cell layers of a common buzzard (Buteo buteo). The recorded results revealed that the neural retina of common buzzard consisted of seven distinct cell layers. The inner nuclear layer was markedly revealed as the thickest one among these layers. A highly melanized RPE was recorded in between the choroid and neural retina. Histologically, the RPE was represented by a single layer of cuboidal epithelial cells with centrally located nucleus. Ultrastructurally, the RPE cells showed numerous melanosomes, mitochondria, phagosomes, myeloid bodies, smooth endoplasmic reticulum (SER), but very rare rough endoplasmic reticulum (RER). The photoreceptor cell layer was represented by three categories of photoreceptor cells: few single rods, numerous single and double cones. Each double cone consisted of a short accessory cone and a long principle cone. The photoreceptor outer segment consisted of bi-membranous discs that are enclosed by outer membrane. Moreover, the inner segment of rods consisted of an ellipsoid and an inner hyperboloid. The hyperboloid was rich with RER, polysomes, Golgi apparatus and autophagic vacuoles. Furthermore, the inner segment of single cone and accessory cone consisted of an ellipsoid, paraboloid and myoid regions, while, the inner segment of principle cone lacked the paraboloid regions. At the proximal end of each inner segment for all types of cones, there was a large heterogeneous oil droplet. The paraboloid region was markedly rich with glycogen granules. The myoid region exhibited the same organelles but with little glycogen granules when compared with hyperboloid.