Fine structure of the pecten oculi in the American crow (Corvus brachyrhynchos)

Ultrastructural and SEM-EDX Analysis Characterizations of the Pecten Oculi of the Eurasian Stone-Curlew (Burhinus oedicnemus): New Insights to Its Migratory Adaptations With Northern Egyptian Coast

Our study represents the first attempts to describe the ultrastructure features in addition to SEM-EDX analysis of the pecten oculi of the nocturnal, visually active Eurasian stone-curlew. The present study was carried out on 10 normal pecten oculi from the migrant Eurasian stone-curlew (Burhinus oedicnemus) that was captured from the Northern Egyptian coast, Edku Lake, Edku, Behera, Egypt. The intraocular folded quadrilateral fan black pecten oculi was observed on the posteroinferior wall of the eyeball. The pecten oculi had 18-20 pleats, with narrow spaces in-between. Our SEM findings showed a tortuous, coiled pecteneal surface due to numerous blood capillaries. The apical part was oriented toward the ciliary body, but the basal part was derived from the retina, just behind the optic nerve. The outer pleat surfaces are covered by the vitreopecteneal limiting membrane, which carries numerous hyalocyte cells on the outer pleat surface. The transverse sections revealed numerous blood capillaries surrounded by numerous melanin granules. Each basal part was surrounded by a thin, elevated ridge. Our SEM-EDX analysis revealed that carbon is the highest (half percent), oxygen represents about one-third, and nitrogen is one-fifth percent of all elements. The lowest elements are sulfate at the apical part and phosphorus in the middle and basal parts. In conclusion, our findings reveal that the number of pecteneal pleats is related to the nocturnal active visual pattern and the lifestyle of this migratory bird.

Pecten oculi of kestrel (Falco tinnunculus rupicolaeformes) and little owl (Athene noctua glaux): Scanning electron microscopy and histology with unique insights into SEM-EDX elemental analysis

There is scanty data about the comparative morphological features between the pecten oculi of two carnivorous birds with different visual active clock hours: the diurnal common kestrel and the nocturnal little owl. This study illustrated the comparative gross, scanning electron microscopy, and histological characteristics between pecten oculi of kestrel and little owl. This study first attempts to describe the scanning electron microscopy-energy dispersive x-ray (SEM-EDX) elemental analysis at the parts (apex, middle, and base) of the pecten oculi of these two birds. The present study results observed the same position, origin, directions, parts, convoluted outer pleat surfaces, and SEM-EDX elemental analysis, but there were some minor variations due to the different visual active clock hours. These minor variations were summarized in the following points: pleat number (21-23 in the kestrel and 10-11 in the owl), shape (fan rhomboid in the kestrel and accordion in the owl), inter-pleat spaces (wider in the kestrel than in the owl), pigmentations (highly black pigmented in the owl than in the kestrel), hyalocyte cell aggregations (highest in the middle and dwindling at the apex and base in the kestrel, while highest in the middle and base and dwindling at the apex in the owl), and SEM-EDX elemental analysis percentage. SEM/EDX elemental analysis confirmed the presence of oxygen (the highest one), carbon, nitrogen (the second one), nitrogen (the third one), and aluminum (the lowest one) in varying percentages within the pecten oculi; these findings contribute to our understanding of its structural, adaptations with different visual active clock hours, and functional characteristics. RESEARCH HIGHLIGHTS: This study compared the pecten oculi of two carnivorous birds with different visual active clock hours: the diurnal common kestrel and the nocturnal little owl. Anatomically, the characteristic features were similar in both the birds, but some minor variations were observed adapted to their visual active clock hours. The pecten oculi of both birds were analyzed using SEM-EDX for elemental analysis, and it revealed that oxygen was the highest elemental concentration, followed by carbon and nitrogen. Aluminum concentrations were small as per SEM-EDX analysis. The study suggested that the pecten oculi of these birds are related to their active visual clocks and adaptive nutritional mechanisms.

Macroscopic and microscopic comparison of pecten oculi in different avian species

The current study aims to present differences between the pecten oculi of different avian species through morphologic, macroscopic, light, and electron microscopic examinations. The study is a comprehensive research on seven avian species (sparrowhawk, hawk, magpie, swan, heron, pheasant, duck). The right eyes of the animals utilized in the study were removed for light microscopic examination, whereas their left eyes were removed for electron microscopic and macroscopic examinations. Morphometric analyses, as well as stereo and light microscopic measurements, were carried out on the pecten oculi of the animals. Given all these data, it was determined that the height of the pecten oculi did not differ among the species in the study; however, the pecten oculi were larger in birds with the highest value compared to the other species in the macroscopic measurements. Also, the pecten oculi vessels were larger, and the number of melanocytes was higher in keen eyesight, raptor, and migratory birds with large bulbus oculi. All these data suggest that the pecten oculi not only supplies nutrient to the retina but also contributes to sharp vision during migration and hunting, UV absorption from sunlight, as well as preservation of intraocular equilibrium.

Biological features of the pecten oculi of the European wild quail (Coturnix coturnix): Adaptative habits to Northern Egyptian coast with novel vision to its SEM-EDX analysis

The present investigation was prepared to give a complete ultrastructural characterization of the pecten oculi of the diurnal European wild Quail to describe their adaptation habits to the Northern Egyptian coast. Our work declares the first endeavor is the elemental analysis using scanning electron microscopy-energy dispersive X-ray (SEM-EDX) to show the migration effect on their eye. The intra-ocular quadrilateral trapezoid black pigmented plicated type pecten oculi were observed on the postero-inferior wall of the eyeball with craniocaudal and posterio-anterior directions along the fetal fissure. The pecten oculi consist of three parts: the basal, body, and apical. The basal part originated behind the optic nerve, forming the slightly elevated border, while the apical part was directed toward the ciliary body. There are 10-11 pleats with interpleat space. The coiled surface refers to numerous capillary vessels. The smooth head of each pleat was kidney-like, strongly attached to a bridge. The vitreopecteneal limiting membrane separated the pecten oculi from the vitreous body. There are numerous melanosomes and little hyalocytes on the pecteneal pleat's outer surfaces. The thick basal part of each pleat had numerous thick longitudinal microfolds that refer to the numerous blood capillaries attached to the retina as supporting roots. SEM/EDX elemental analysis revealed that carbon is the highest element (half), while oxygen represents about one-third. In the meantime, the lowest element is the phosphate at the apical part, while the lowest element in the rest is the sulfate. Finally, the pecten oculi are thought to be a reflection of the avian lifestyle and ecological adaptations. HIGHLIGHTS: Our work is the first description of the elemental analysis using SEM-EDX to show the migration effect on their eye. The quadrilateral trapezoid black pigmented plicated type pecten oculi were observed on the postero-inferior wall of the eyeball with cranio-caudal and posterio-anterior directions along the fetal fissure. The basal part of the pecten oculi originated behind the optic nerve, forming the slightly elevated border, while the apical part was directed toward the ciliary body. There are 10-11 pleats with interpleat space. The vitreopecteneal limiting membrane separated the pecten oculi from the vitreous body. There are numerous melanosomes and little hyalocytes on the pecteneal pleat's outer surfaces. SEM/EDX elemental analysis revealed that carbon is the highest element (half percent), while oxygen represents about one-third of the element's percent meanwhile, the lowest element is phosphate at the apical part, while the lowest element in the rest is the sulfate.

Gross, ultrastructural, and histological characterizations of pecten oculi of the glossy ibis (Plegadis falcinellus): New insights into its scanning electron microscope-energy dispersive X-ray analysis

The current study shows the first attempts to clarify the gross, ultrastructure, and histological properties of the pecten oculi of the diurnal, visually active glossy ibis, as well as scanning electron microscope-energy dispersive X-ray (SEM-EDX) image analysis (Plegadis falcinellus). The pecten oculi was found on the eyeball's posteroinferior wall, adjacent to the optic nerve in both the craniocaudal and posterio-anterior directions. The plicated quadrilateral black pigmented pecten oculi consisted of a base, 10-12 pleats, and an apex. The base was joined by an elevated ridge and derived from the non-vascular retina, while the apex was not a fused part and was found neighboring the gelatinous vitreous body. The limited interpleat spaces were somewhat wider at the base of the pecten oculi. The outer surface of each highly vascular pecten pleat revealed a tortious coiled formation due to the existence of a considerable number of capillary vessels. The outer pleat surfaces had a vitreopecteneal limiting membrane that segregated the pecten pleats from the vitreous body. The high SEM magnification revealed that there are considerable plentiful hyalocyte cells on the outer surface of the pleats. The SEM-EDX analysis of the elementary formatting of the pecten oculi (at apex, middle, and base) clarified that the carbon represents the highest and a half percent. Furthermore, oxygen represents one-third of all elemental composition in the three regions, while the lowest percentage is calcium. Finally, the pecten oculi characterizations of this migratory bird on the Northern Egyptian shore were associated with their adaptive dietary strategies.

Ultrastructural characterizations of the pecten oculi of the common ostrich (Struthio camelus): New insight to scanning electron microscope-energy dispersive X-ray analysis

The current observation was designed to give a complete ultrastructural description of the pecten oculi of the common ostrich (Struthio camelus). Moreover, this study represents the first attempt to measurements the elements composition of the pecten oculi using scanning electron microscope-energy dispersive X-ray (SEM-EDX) at three regions (apical, body, and basal). To accomplish this study, eight ostrich were examined grossly and under the electron microscope. The vaned-shaped pecten oculi consisted of three regions (apex, body, and base) with 24-25 plates. The pecten oculi was located postero-anteriorly near to the optic nerve disc that was attached by their bases to the retina forming a slightly elevated basal border joining the bases of all pleats, while the apex was linked in a circular bridge. The pleats are separated from each other by the inter-pleat spaces that are very clear at the base and nearly not observed at the apical part. The outer pleat's surface carried numerous prominences that pointed to the existence of numerous afferent and efferent pecteneal blood capillaries vessels. The vitreopecteneal limiting membrane separated the pecten oculi from the vitreous body. Our findings concluded that, the high number of thick pecteneal pleats was related to the diurnal activity of the common ostrich. SEM-EDX shows that the carbon percentage in the three regions is the highest that representing about half of all elements, while the oxygen percent is about one-third; meanwhile, the lowest percentage is the sulfate at the apical region, and the calcium at the body and basal regions.

Morphological and Ultrastructural Studies of Pecten in the Eurasian Tree Sparrow

We studied the fine histological structures of pecten oculi of the Eurasian tree sparrow using various microscopy techniques. The pecten of the tree sparrow was found to be of a pleated type comprising of pleats, bridges, and base. The light microscopic study revealed further that the pleats consist of capillaries of varying sizes, blood vessels, and numerous pigmented cells that give them a black color. Histochemical studies of pecten showed a large deposition of lipid droplets, which were more abundant in the basal area. The transmission electron microscopy displayed capillaries and blood vessels that remain surrounded by a thick fibrous basal membrane. They are formed of endothelial cells having a large lumen and abluminal area with microfolds. Interstitial spaces were found filled with rounded melanocytes, electron-dense pigment granules, and mitochondria. Observations under the scanning electron microscope revealed the presence of a dense vascular network of capillaries and vessels. In addition, large hyalocytes were also observed on the surface of the pleats. The above observations suggest that the histological structure of the pecten of the tree sparrow resembles those present in the pecten of other diurnal birds. However, further investigation is required to ascertain its functional role in birds.

Ultrastructural studies of the pecten oculi of the Garganey (Anas querquedula, Linnaeus 1758) and the Eurasian common moorhen (Gallinula chloropus chloropus, Linnaeus 1758)

The present study represents the first attempts to give a full anatomical comparison of the vascular pigmented pectin oculi of the diurnal activity Anas querquedula and Gallinula chloropus chloropus. For achievement of this work, 10 mature birds from each species were examined under stereo- and electron microscope. The pecten oculi of A. querquedula is triangular fan-like, while in Gallinula c. thin like-fold. In both examined birds, the pecten oculi located postero-anteriorly intraocular just adjacent to optic nerve disc and attached to the retina by its base, while the free apex projected into vitreous body. A. querquedula had 14-15 pleats, while Gallinula c. chloropus had 22-24 pleats. In A. querquedula, all pecten pleats connected to each other apically by a connecting bridge. The pecten oculi was plicated type in A. querquedula, but folded type in Gallinula c. chloropus. In A. querquedula, the external surface of the pleats head carried 8-10 transverse ridges, in addition to the external and lateral surface of the pleat body carried numerous round prominences that indicated the presence of numerous afferent and efferent vessels. In both examined birds, there is a retinal elevated fold situated parallel to the slightly elevated basal fold which is clear and thicker in A. querquedula than in Gallinula c. chloropus. In Gallinula c. chloropus, the transverse section shows that the pleats had numerous afferent and efferent vessels capillaries. Statistical analysis comparing the relative measurements of the pecten oculi in the two examined birds showed that there was a significant difference.

Light and electron microscopic studies on the pecten oculi showing blood-retina barrier properties in Turkey's native Gerze chicken

The pecten oculi is a highly vascularized and pigmented organ that projects from the optic disc into the vitreous body in the avian eye. In this study, the pecten oculi of Turkey's native Gerze chicken was examined by light and scanning electron microscopy. Furthermore, the localization of some adherens junction components (E-cadherin and pan-cadherin) in intact vessels of the blood-retina barrier was investigated by immunohistochemistry. In the Gerze chicken, the pecten oculi was a thin structure, which was located over the head of the discus nervi optici and projected from the retina into the corpus vitreum. The pecten oculi consisted of 18-21 highly vascularized pleats, joined apically by a bridge and resembled an accordion in appearance. Hyalocytes and melanocytes were observed around the small and large vessels. The morphometric data of the pecten oculi showed that there were no statistical differences in terms of sex. The immunohistochemical analysis of the pecten oculi, which is used as a model for the investigation of the formation and maturation of the barrier properties in the central nervous system, revealed cytoplasmic E-cadherin and pan-cadherin immunoreactivity in the endothelial cells of the small, large and capillary vessels. These observations suggest that while the morphological and histological structure of the Gerze chicken's pecten oculi was generally similar to that of other diurnal domestic birds, the pecten oculi, a model system for vascular differentiation and the blood-retina barrier, expressed different cadherins.

A comparative ultrastructural study of the pecten oculi in adult, juvenile, and nestling yellow-legged gulls, Larus michahellis (Naumann, 1840)

This study aimed at examining the histological structure of the pecten oculi in the adult yellow-legged gull, Larus michahellis, and at two moments of postnatal development: during the posthatch (nestling) and juvenile periods. Particular attention was paid to differences in the diameter of vessels, the thickness of the basement membrane, and ultrastructural features of endothelial and pigmented stromal cells. Capillary endothelial cells displayed numerous microvillous-like folds projecting from their internal and external surfaces. Intercellular spaces between capillaries were occupied by pigmented stromal cells. The ultrastructure of pecten oculi underwent noticeable changes during postnatal development. The examination of the capillaries in nestlings, juveniles, and adults revealed that the formation process of vessels and pigmented stromal cells did not complete itself in the posthaching phase. The prominent feature of endothelial cells of capillaries in nestlings was that the microvilli were longer than in juvenile and adult cells, and the capillary lumen was therefore reduced. In this sense, their pigmented stromal cells showed fewer melanosomes, lacked intercellular spaces, and cellular junctions could still be observed. These results provide evidence that the pecten oculi during the posthatching phase maintains immature morphological features consistent with a role of pigmented stromal cells in the blood-retina barrier.

Macroanatomic, light, and electron microscopic examination of pecten oculi in the seagull (Larus canus)

The present study was conducted to determine macroanatomic characteristic as well as light and electron microscopic examination (SEM) of pecten oculi and totally 20 bulbus oculi belonging to 10 seagulls (Larus canus) were used. Pecten oculi formations consisted of 18 to 21 pleats and their shape looked like a snail. Apical length of the pleats forming pecten oculi were averagely measured as 5.77 ± 0.56 mm, retina-dependent base length was 9.01 ± 1.35 mm and height was measured as 6.4 ± 0.62 mm. In pecten oculi formations which extend up to 1/3 of the bulbus oculi, two different vascular formations were determined according to thickness of the vessel diameter. Among these, vessels with larger diameters which are less than the others in count were classified as afferent and efferent vessels, smaller vessels which are greater in size were classified as capillaries. Furthermore, the granules which were observed intensely in apical side of the pleats of pecten oculi were observed to distribute randomly along the plica.

Scanning Electron Microscopic Studies of the Pecten Oculi in the Quail (Coturnix coturnix japonica)

The main purpose of this study is to extend the microscopic investigations of the pecten oculi in the quail in order to add some information on the unresolved functional anatomy of this unique avian organ. The pecten oculi of the quail was studied by scanning electron microscopy. Eighteen- to-twenty two highly vascularised accordion-like folds were joined apically by a heavily pigmented bridge of tissue, which holds the pecten in a fanlike shape, widest at the base. The structure of the double layered limiting membrane was recorded. The presence of hyalocytes with macrophage-like appearance was illustrated. It is assumed that the pecten oculi of the quail resembles that of the chicken. Illustrated morphological features of this species may add information on the active physiological role of the pecten. But still, the functional significance of this organ is a matter of controversies.

Macroanatomic, light and scanning electron microscopic studies of the pecten oculi in the stork (Ciconia ciconia)

This study was undertaken to investigate the pecten oculi of stork by using macroscopic, light and electron microscopic techniques. A total of 20 eyes that were obtained from 10 storks were used. The eyes were cleaned and isolated by dissection. After various procedures, four of the pecten oculi were examined by light microscope while the other four with an electron microscope. The remaining 12 eyes were assigned for macroscopic investigation. Pecten oculi of the stork were determined as accordion-like structures that originated from n. opticus, consisting of 15-17 plica and projecting up to 2/5 of the diameter of the bulbus oculi. Light microscopic examination revealed two types of blood vessels. Afferent-efferent vessels were larger in diamater (40-45 µm), fewer in numbers, and the capillary vessels were smaller in diamater (2-5 µm) and more in numbers. There were granules including amount of melanin pigment at the apical part of the pleats. These granules were fewer and scattered randomly on the basal part of the pleats. As a result, pecten oculi in the stork, which is a migrating bird, were determined to be similar to those of other diurnal birds.

The morphology of the pecten oculi in the common buzzard (Buteo buteo)

OBJECTIVE

The pecten oculi are an intraocular, vascular, and pigmented structure peculiar to the avian eye. In this study, we investigated the pecten oculi of the common buzzard (Buteo buteo) using stereomicroscopy and light and scanning electron microscopy (SEM).

PROCEDURES

Twenty eyes from 10 adult buzzards were studied. Specimens from each buzzard were preserved in 10% buffered formalin and observed stereomicroscopically before being embedded in paraffin, sectioned, and stained with three stains: Mallory's triple staining technique as modified by Crossman, Hematoxylin-Eosin (HE), and Safranin O, and for examination by light microscopy. Specimens from two buzzards were also prepared for SEM.

RESULTS

Stereomicroscopy and SEM examination showed the pecten oculi in the common buzzard to be pleated-consisting of 17-18 100 μm thick folds. These folds are connected to one another by bands of connective tissue extending vertically between the plications. Blood vessels, approximately 30-40 μm in diameter, were seen on the surface of the each fold. These vessels arise from the base of pecten, becoming thinner toward the apical end of the structure. A network of capillary vessels at the base of the plicated structure resembles contour lines. At high amplification, melanin granule accumulations were observed around the vascular structures of the plica on SEM images. Light microscopy supported the SEM observations.

CONCLUSIONS

These findings reveal that the pecten oculi in the common buzzard are plicated and are remarkably similar to that of the other diurnal raptors.

The morphology of the pecten oculi of the ostrich, Struthio camelus

The pecten oculi is a structure peculiar to the avian eye. Three morphological types of pecten oculi are recognized: conical type, vaned type and pleated type. The pleated type has been well studied. However, there exists only scanty data on the morphology of the latter two types of pectens. The structure of the vaned type of pecten of the ostrich, Struthio camelus was investigated with light and electron microscope. The pecten of this species consists of a vertical primary lamella that arises from the optic disc and supports 16-19 laterally located secondary lamellae, which run from the base and confluence at the apex. Some of the secondary lamellae give rise to 2 or 3 tertiary lamellae. The lamellae provide a wide surface, which supports 2-3 Layers of blood capillaries. Pigmentation is highest at the distal ends of the secondary and tertiary Lamella where blood capillaries are concentrated and very scanty on the primary and the proximal ends of the secondary lamella where the presence of capillaries is much reduced. In contrast to the capillaries of the pleated pecten, the endothelium of the capillaries in the pecten of the ostrich exhibits very few microvilli. These observations suggest that the morphology of the pecten of the ostrich, a flightless ratite bird is unique to the pleated pecten and is designed to meet the balance between optimal vision and large surface area for blood supply and yet ensuring it is kept firmly erect within the vitreous.

Modifications of the falciform process in the eye of beloniformes (Teleostei: Atherinomorpha): evolution of a curtain-like septum in the eye

In order to comparatively analyze curtain-like septa in the eyes of visually orientated "close-to-surface-predators" among atherinomorph teleosts, we examined the eyes of 24 atherinomorph species under a binocular microscope with regard to the falciform process and related structures in the vitreous cavity. Additionally, falciform process samples were analyzed by transmission electron microscopy. All the studied representatives of the Cyprinodontiformes and Atheriniformes, and of one of the beloniform suborder, Adrianichthyioidei, possess a "typical" processus falciformis. In the eyes of the representatives of the other beloniform suborder, Belonoidei, however, pigmented structures that originate in the region of the optic disc and protrude into the vitreous cavity were noted. In the Hemiramphidae (halfbeaks) and Exocoetidae (flying fishes) these pigmented structures have a more cone-like shape, whereas in the Belonidae (needlefishes) and Scomberesocidae (sauries) horizontally oriented heavily pigmented curtain-like septa occur that divide the vitreous cavity dorsoventrally. It is suggested that the "typical" processus falciformis represents a plesiomorphic feature within the Atherinomorpha, whereas the pigmented modifications of the falciform process must be seen as a synapomorphic character state of the Belonoidei. The curtain-like septum of the Belonidae and Scomberesocidae might have evolved from the cone-like structures that are found in the Exocoetoidea. The functional significance of the pigmented structures in the eye is as yet not clear, except for the curtain-like septum found in Belonidae. It might play a role in visual orientation near the water surface at Snell's window.

Fine structure of the pecten oculi of the emu (Dromaius novaehollandiae)

The pecten oculi of the emu (Dromaius novaehollandiae) has been examined by light and electron microscopy. In this species the pecten is small relative to the size of the globe and is of a primitive pleated type. It consists of only 3-4 loose folds that are joined apically by a bridge of tissue which holds the pecten in a fan-like shape widest at its base. Each fold is quite thick (100-120 microns) and has a central core of mostly unpigmented cell processes. In this central region are supply or drainage vessels while numerous melanocytes and pecteneal capillaries are only located at the periphery of the folds. The capillaries are extremely specialized for transport functions and for the most part display extensive microfolds on both their luminal (inner) and abluminal (outer) borders although capillaries with very few microfolds are also noted. An unusual feature of some capillaries is luminal folds of the cell body with further luminal microfolds superimposed on them. Except for the nuclear region which contains most of the organelles, the endothelial cell bodies are extremely thin. These capillaries are surrounded by thick fibrillar basal laminae which are felt to be structurally important. Pericytes are a common feature within the basal lamina of these capillaries. The numerous peripherally located melanocytes which more or less surround the capillaries are also presumed to be important for structural support of the pecten. The large number of cell processes forming the central core of each fold are felt to be unpigmented processes of the melanocytes.