Morphological and morphometric study of the pecten oculi in the budgerigar (Melopsittacus undulatus).

The pecten oculi is a highly vascular and pigmented organ placed in the vitreous body of the avian eye. As no data are currently available on the morphological organization of the pecten in the Psittaciformes, the pecten oculi of the budgerigar (Melopsittacus undulatus) was studied. The eyes from adult male budgerigars were examined by light, transmission, and scanning electron microscopy and a morphometric study on both light and transmission electron microscopy specimens was also performed in the different parts of the organ. In the budgerigar, the type of the pecten oculi was pleated. Its basal part had a cranio-caudal and postero-anterior course; its body consisted of 10-12-folds joined apically by a densely pigmented bridge. The pecten showed many capillaries, whose wall was thick and formed by pericytes and endothelial cells. These latter had a large number of microfolds, rectilinear on their luminal surface and tortuous on their abluminal surface. Interstitial pigment cells were placed among the capillaries, filled with melanin granules and showed many cytoplasmic processes. The morphometric analysis demonstrated significant differences among the three parts of the organ relative to the length of the endothelial processes and to the number and size of the pigment granules. The morphological and morphometric analysis showed that the bridge of the budgerigar, different from the other birds, had a large number of capillaries, so that this part of the organ could also play a trophic role for the retina in addition to the choriocapillaris.