Morphological and Morphometric Study of the Pecten Oculi in the Budgerigar (Melopsittacus undulatus)

Abstract

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. Anat Rec, 295:540-550, 2012. V V C 2012 Wiley Periodicals, Inc.

Peçeli Baykuşlarda (Tyto alba) Pecten Oculi’nin Işık ve Elektron Mikroskopik Yapısı

“…Capillaries were more abundant and were located among the primary and secondary vessels. We did not find any lymph vessels in the pecten oculi, unlike in the mallard (Anas platyrhynchos) [13] ; this is in accordance with studies on other species [21,24] .…”

“…The pecten oculi of the common barn owl had three different parts, in accordance with the literature: a basal part located near to where the optic nerve enters the eye, pleats arising from the basal part, and an apical part where the pleats merge [21] .…”

“…Several studies have indicated that visually more active species have larger pecten oculi consisting of more pleats compared to bird species with less visual activity [21,26,27] . Accordingly, diurnal species, which require visual acuity have larger pecten oculi with more pleats than nocturnal bird species requiring visual sensitivity [17,27] .…”

“…Although the presence of a vitreo-pecteneal limiting membrane covering the pecten oculi has been reported in all bird species [9,26,38] , macrophage-like hyalocytes around this connective tissue have been observed only in some species including the chicken [38,39] , budgerigar [21] , quail [23,40] , mallard [41] and emu [35] and not in the pigeon [42] , redtailed hawk [19] , or nighthawk [1] . We also found a vitreopecteneal limiting membrane in the common barn owl.…”

“…Numerous studies have examined the morphological and histological structures of the pecten oculi using both light and electron microscopy in the great horned owl (Bubo virginianus) [18] , red-tailed hawk (Buteo jamaicensis) [19] , common buzzard (Buteo buteo) [20] , budgerigar (Melopsittacus undulates) [21] , black kite (Milvus migrans) [22] , quail (Coturnix coturnix japonica) [23] , pigeon (Columba livia) [10] , stork (Ciconia ciconia) [24] , and jungle crow (Corvus macrorhynchos) [25] . Studies on the morphological and histological structures of the pecten oculi in different owl species including nighthawk (Chordeiles minor) [1] , great horned owl (Bubo virginianus) [18] , barred owl (Strix varia) [26] , spotted eagle owl (Bubo africanus) [27] have been published.…”