Light and electron microscopy study of the pecten oculi of the Jungle Crow (Corvus macrorhynchos)

Abstract

Summary: In this study, the pecten oculi of a diurnally active bird, the Japanese jungle crow (Corvus macrorhynchos), was examined using light and electron microscopy. In this species, the pecten consisted of 24-25 highly vascularized pleats held together apically by a heavily pigmented 'bridge' and projected freely into the vitreous body in the ventral part of the eye cup. Ascending and descending blood vessels of varying caliber, together with a profuse network of capillaries, essentially constituted the vascular framework of the pecten. A distinct distribution of melanosomes was discernible on the pecten, the concentration being highest at its apical end, moderate at the crest of the pleats and lowest at the basal and lateral margins. Overlying and within the vascular network, a close association between blood vessels and melanocytes was evident. It is conjectured that such an association may have evolved to augment the structural reinforcement of this nutritive organ in order to keep it firmly erectile within the gel-like vitreous. Such erectility may be an essential prerequisite for its optimal functioning as well as in its overt use as a protective shield against the effects of ultraviolet light, which otherwise might lead to damage of the pectineal vessels.

A Comparative Morphometrical Study of the Pecten Oculi in Different Avian Species

“…Pigmented cells were observed around the capillaries in this study. The close association between the pigmented cells and the capillaries has been also reported in the black kite [1], quail [5], ostrich [2], and jungle crow [9]. It has suggested that pigmented cells provide the structural reinforcement to pecten oculi for keeping it firmly erectile within the gel-like vitreous and also protect the blood vessels against damage from ultraviolet light [1, 7, 17].…”

“…In this the study number of pleats of the pectens was 12, 13-14, 21-22, and 17 in duck, pigeon, turkey, and starling, respectively. Previous studies have demonstrated that other diurnal species such as domestic fowl has 16–18 [15], black kite has 12-13 [1, 15], quail has 19 [5], common buzzard has 17-18 [3], jungle crow has 24-25 [9], mallard has 12–14 [8] folds in pectin. However nocturnal birds have small pectens such as barred owl that has 8–10 [16] and spotted eagle owl that has 5-6 [15] folds in pecten.…”

“…The conical type is only reported in the brown kiwi ( Apteryx mantelli ); the vaned type is present in ostriches ( Struthio camelus ) and rheas ( Rhea americana ) [6]; and pleated form is widely reported in most birds (neognathae) such as quail [5], black kite [1], galah [7], common buzzard [3], mallard [8], pigeon [4], and jungle crow [9]. The size of the pecten depends on the visual requirements of the bird, so that daily active bird species have a relatively large and highly complex pecten oculi with many folds while night active bird species will have a relatively small and simple pecten oculi [6].…”

Doppler ultrasonography of the <i>pectinis oculi</i> artery in harpy eagles (<i>Harpia harpyja</i>)

“…as found in ostriches, rheas, and tinamous), or 3) pleated (e.g. as found in all the other avian species) (Brach, 1977;Baumel, 1993;Montiani-Ferreira, 2001;Kern, 2006;Kiama et al, 2006;Rahman et al, 2010;Micali et al, 2012;Mustafa and Ozaydjn, 2013). Other than a structure providing nutritional support for the anangiotic retina (Rodriguez-Peralta, 1975), the pecten oculi has been hypothesized to function in intraocular pH and pressure regulation (Brach, 1975), stabilization of the vitreous body (Tucker, 1975), reduction of intraocular glare and maintenance of intraocular pressure (Seaman and Himelfarb, 1963), and in maintenance of the blood ocular barrier for the retina and vitreous body (Barlow and Ostwald, 1972).…”

“…As with all avian species, an anangiotic retina leaves the inner retinal layers without a direct blood supply, therefore limiting delivery of nutrients and rapid removal of wastes. However, a vascular structure called the pecten oculi is found projecting anteriorly from the optic disc into the vitreous body of all birds (class Aves or clade Avialae) (Brach, 1977;Kern, 2006;Kiama et al, 2006;Rahman et al, 2010;Micali et al, 2012;Mustafa and Ozaydjn, 2013). Pecten oculi are pigmented, vascularized, and are traditionally classified into one of three morphologies: 1) conical (e.g.…”