Tapetum Fibrosum Research Articles

Morphological Aspects and Microscopic Analyses of Fibrous Tunic and Uveal Components in Bovine Eye.

This study aimed to reveal the anatomical features of the bovine eye by scanning electron and light microscopic methods. For this purpose, a total of 40 eyes were evaluated. Gross and microscopic characteristics of the cornea, sclera, ciliary body, choroid, iris, and lens were determined. Bowman's and Descemet's membranes of the cornea were quite dense and prominent. Collagen lamellae of the cornea were wavy in the periphery and more parallel to the basal and metachromatic fibroblasts were noted. Three to four ciliary plicae merged to form ciliary processes. The presence of prominent intermediate bands connecting the ciliary plicae was determined. The zonular fibrils merged and attached to the lens in the form of thick zonular bands. A dense corpora nigra was present at the rectangular pupillary border of the iris. Tapetum fibrosum, consisting of polygonal tapetal cells, was in blue-yellow-green color and covered most of the choroid. A complex drainage system consisting of trabecular meshwork, angular aqueous plexus, ciliary sinus, and scleral venous vessels localized in a fairly wide iridocorneal angle was identified. Identifying structural features of the bovine eye is very important and useful for pathological evaluations, understanding species-specific physiological mechanisms and for operative interventions of ruminant species.

Adaptive optics in the Arctic? A commentary on Fosbury and Jeffery.

Adaptive optics in the Arctic? A commentary on Fosbury and Jeffery.

Anatomical and histological structures of eye and lacrimal gland in Norduz andMorkaraman sheep

The current study was conducted to determine the morphological, morphometric, and histological characteristics of bulbus oculi and lacrimal gland in sheep. For this purpose, 28 pairs (n = 7 males and n = 7 females) of bulbus oculi from Morkaraman and (n = 7 males and n = 7 females) Norduz sheep were analyzed. The bulbus oculi in the skulls were dissected from the orbit and removed. The morphometric data such as distance between endpoints of the dissected bulbus oculi in temporal, nasal, and dorsal directions, the length between endpoints of the pupil in dorsal and ventral directions, and as well as in temporal and nasal directions were measured with a digital caliper. For histological analyses, the eye tissues of Norduz and Morkaraman sheep were fixed in 10% formaldehyde solution. Then, the tissues were blocked by paraffin via passing them through the routine histological tissue follow-up solutions. Dissections in 6-μm thickness were made from the blocks. To evaluate the tissues histologically, tissue sections were stained with Crossmann's modified triple staining technique (triple staining). The mean values and standard deviations of the acquired data and the correlation coefficients among these characters were evaluated by the SPSS 22 program. The dorso-ventral diameter of bulbus oculi (BDV) was measured as an average of 25 ± 0.95 and 26.67 ± 3.19 mm in female and male Norduz sheep, respectively. Similarly, the BDV diameter in Morkaraman sheep was measured as 26.19 ± 1.04 mm in females and 26.41 ± 0.92 mm in males. As a result of analysis between genders in Norduz sheep, the BDV diameter, medio-lateral diameter of cornea (CML), dorso-ventral diameter of pupil (PDV), and dorso-ventral diameter of lens (LDVÇ) were identified statistically significant (p < 0.05). However, the results of the gender analysis in Morkaraman sheep demonstrated that none of the parameters were statistically significant (p > 0.05). The eye layers, the tunica fibrosa bulbi, tunica vasculosa bulbi, and tunica interna bulbi of both male and female Morkaraman and Norduz sheep were studied through the microscopic analysis. It was specified that both sheep species and both genders had a very wide tapetum fibrosum structure in the choroid of eye structures. It was also determined that the lacrimal gland had a seromucous characteristic and a tubuloacinar structure.

Retinal Topography in Two Species of Baleen Whale (Cetacea: Mysticeti)

Little is known about the visual systems of large baleen whales (Mysticeti: Cetacea). In this study, we investigate eye morphology and the topographic distribution of retinal ganglion cells (RGCs) in two species of mysticete, Bryde’s whale (Balaenoptera edeni) and the humpback whale (Megaptera novaeanglia). Both species have large eyes characterised by a thickened cornea, a heavily thickened sclera, a highly vascularised fibro-adipose bundle surrounding the optic nerve at the back of the eye, and a reflective blue-green tapetum fibrosum. Using stereology and retinal whole mounts, we estimate a total of 274,268 and 161,371 RGCs in the Bryde’s whale and humpback whale retinas, respectively. Both species have a similar retinal topography, consisting of nasal and temporal areas of high RGC density, suggesting that having higher visual acuity in the anterior and latero-caudal visual fields is particularly important in these animals. The temporal area is larger in both species and contains the peak RGC densities (160 cells mm^–2 in the humpback whale and 200 cells mm^–2 in Bryde’s whale). In the Bryde’s whale retina, the two high-density areas are connected by a weak centro-ventral visual streak, but such a specialisation is not evident in the humpback whale. Measurements of RGC soma area reveal that although the RGCs in both species vary substantially in size, RGC soma area is inversely proportional to RGC density, with cells in the nasal and temporal high-density areas being relatively more homogeneous in size compared to the RGCs in the central retina and the dorsal and ventral retinal periphery. Some of the RGCs were very large, with soma areas of over 2,000 µm². Using peak RGC density and eye axial diameter (Bryde’s whale: 63.5 mm; humpback whale: 48.5 mm), we estimated the peak anatomical spatial resolving power in water to be 4.8 cycles/degree and 3.3 cycles/degree in the Bryde’s whale and the humpback whale, respectively. Overall, our findings for these two species are very similar to those reported for other species of cetaceans. This indicates that, irrespective of the significant differences in body size and shape, behavioural ecology and feeding strategy between mysticetes and odontocetes (toothed whales), cetacean eyes are adapted to vision in dim light and adhere to a common “bauplan” that evolved prior to the divergence of the two cetacean parvorders (Odontoceti and Mysticeti) over 30 million years ago.

Relationship between Distribution of Tapetum Fibrosum and Retinal Pigment Epithelium in the Sheep Eye

The tapetum lucidum is a light-reflective device improving visual sensitivity in mesopic vision. There have been few studies on tapetal distribution and its relationship with degree of pigmentation in the retinal pigment epithelium (RPE). In the present study, sheep's eyes were used for macroscopical observation of the tapetum, and then histological sections of the posterior eyecups were made to analyze the distribution of tapetal thickness and degree of pigmentation in the RPE. Macroscopically, with available light, the tapetum was located in the dorsal eye fundus to the optic disc and showed an L-shape with the horizontally elongated nasal part and the dorsally expanded temporal part. In photographs with a flash, the tapetal area expanded and showed a more triangular shape. The tapetum histologically consisted of layers of dense collagen fibers and was thicker in the temporal part than in the nasal part. The maximum tapetal thickness was approximately 70 microm. The histological tapetal area was similar to the tapetal shape with a flash light. The pigmentation of the RPE was divided into three types, nonpigmented, transitional, and pigmented areas. The nonpigmented area was similar to the tapetal shape with available light. It is suggested that approximately 55% of the histological tapetal area is covered with the nonpigmented area and is functional under a natural light condition. The functional tapetal area was similar to the L-shaped high-density area of retinal ganglion cells.

Comparative morphology of the tapetum lucidum (among selected species).

The phenomenon of 'eye-shine' is seen in a variety of animal species, and is generally thought to be related to the presence of an intraocular reflecting structure, the tapetum lucidum. The tapetum lucidum is a biologic reflector system that is a common feature in the eyes of vertebrates. It normally functions to provide the light-sensitive retinal cells with a second opportunity for photon-photoreceptor stimulation, thereby enhancing visual sensitivity at low light levels. The tapetum lucidum is presented here according to a classification based on the location, as well as the composition, of this reflective layer. Finally, the physical and chemical properties, as well as the origins of the different tapeta lucida, are discussed and compared. The anatomic and biochemical aspects of the tapetum lucidum in various vertebrates are examined. Morphologic observations were made from paraffin and plastic embedded specimens. Specimens were treated with traditional stains and observed by light and transmission electron microscopy. Some species (primates, squirrels, birds, red kangaroo and pig) do not have this structure and they usually are diurnal animals. In vertebrates, the tapetum lucidum exhibits diverse structure, organization and composition. Therefore, the retinal tapetum (teleosts, crocodilians, marsupials, fruit bat), the choroidal guanine tapetum (elasmobranchs), the choroidal tapetum cellulosum (carnivores, rodents, cetacea), and the choroidal tapetum fibrosum (cow, sheep, goat, horse) are described. The tapetum lucidum represents a remarkable example of neural cell and tissue specialization as an adaptation to a dim light environment and, despite these differences, all tapetal variants act to increase retinal sensitivity by reflecting light back through the photoreceptor layer. These variations regarding both its location and structure, as well as the choice of reflective material, may represent selective visual adaptations associated with their feeding behavior, in response to the use of specific wavelengths and amount of reflectance required.

Evolution of the tapetum. Schwab IR, Yuen CK, Buyukmihci NC, Blankenship TN, Fitzgerald PG. Trans Am Ophthalmol Soc 2002;100:187–200

Ocular specimens of representative fish in piscine families, including Acipenseridae, Cyprinidae, and Chacidae; the reptilian family Corcodylidae; the mammalian family Felidae; and the Lepidopteran family Sphingidae were reviewed and histologically compared. All known varieties of tapeta were examined, classified and compared with the known cladogram representing the evolution of each specific family. Types of tapeta include tapetum cellosum, tapetum fibrosum, retinal tapetum, invertebrate pigmented tapetum, and invertebrate thin-film tapetum. All but the invertebrate pigmented tapetum were examined histologically. Review of the evolutionary cladogram and comparison with known tapeta suggest that the tapetum evolved in the Devonian period 345 to 395 million years ago. Tapeta developed independently in at least three separate orders in invertebrates and vertebrates, and all have surprisingly similar mechanisms of light reflection, including thin-film interference, diffusely reflecting tapeta, Mie scattering, Rayleigh scattering, and possibly orthogonal retroflection. Tapeta are found in invertebrates and vertebrates and display different physical mechanisms of reflection. Each tapetum reflects the wavelengths most relevant to the species’ ecological niche. The authors hypothesize that the tapetum evolved independently in both invertebrates and vertebrates as early as the Devonian period and coincided with an explosion of life forms.—Hans E. Grossniklaus

The visual system of the Florida garfish, Lepisosteus platyrhincus (Ginglymodi). I. Retina.

The retina and choriocapillaris of the Florida garfish, Lepisosteus platyrhincus (Ginglymodi), was examined at the light and electron microscopic levels. The inner limiting membrane is covered by an extensive system of vitreal blood vessels emanating from the hyaloid artery, which enters the eye ventrally at the proximal end of the elongated optic nerve head. Two size classes of ganglion cell soma are segregated by optic axon fascicles and Müller cell endfeet, all of which lie at the level of the ganglion cell layer. A third class of 'displaced' ganglion cells lies at the border of the inner plexiform and inner nuclear layers amidst tightly packed amacrine, bipolar and Müller cell soma. Two layers of horizontal cells lie vitread of a synaptic zone consisting of a complex arrangement of horizontal and bipolar dendrites invaginating rod spherules and cone pedicles to form single and multiple (three to six) synaptic ribbon connections, respectively. Immediately vitread of the photoreceptor nuclei lie a population of 'displaced' bipolars. Three types of photoreceptors are characterised: unequal double cones, single cones (large and small) and rods. These show retinomotor movements where the rods elongate in the light and are masked by the pigment epithelium and contract in the dark as the pigment migrates sclerad. Ultrastructurally, 4 types of dark-staining (osmophilic) granules are described: (1) Small glycogen granules (0.033 microns) aggregated at the bases of the photoreceptor nuclei and larger similar granules (0.078 microns and termed paraboloids) vitread to the ellipsoid; (2) tapetal granules (0.32 microns) distributed throughout the dorsal four-fifths of the retinal pigment epithelium (RPE); (3) pigment granules (0.5-2.0 microns) in the RPE, concentrated in ventral retina; (4) granules or melanosomes (0.813 microns) of the choriocapillaris. The second class of granules constitute a tapetum lucidum eliciting a yellow eyeshine when viewed in the dark. Two other tapeta also exist, a guanine tapetum (irregular guanine crystals) and a tapetum fibrosum (stacks of collagen fibrils). Functional correlations are made, and the putative ancestral (primitive) condition of particular visual characters is established for the ray-finned fishes by out-group comparisons.

The Visual System of the Florida Garfish, &lt;i&gt;Lepisosteus platyrhincus&lt;/i&gt;(Ginglymodi) (Part 2 of 2)

The retina and choriocapillaris of the Florida garfish, <i>Lepisosteus platyrhincus </i>(Ginglymodi), was examined at the light and electron microscopic levels. The inner limiting membrane is covered by an extensive system of vitreal blood vessels emanating from the hyaloid artery, which enters the eye ventrally at the proximal end of the elongated optic nerve head. Two size classes of ganglion cell soma are segregated by optic axon fascicles and M&#220;ller cell endfeet, all of which lie at the level of the ganglion cell layer. A third class of 'displaced' ganglion cells lies at the border of the inner plexiform and inner nuclear layers amidst tightly packed amacrine, bipolar and M&#220;ller cell soma. Two layers of horizontal cells lie vitread of a synaptic zone consisting of a complex arrangement of horizontal and bipolar dendrites invaginating rod spherules and cone pedicles to form single and multiple (three to six) synaptic ribbon connections, respectively. Immediately vitread of the photoreceptor nuclei lie a population of 'displaced' bipolars. Three types of photoreceptors are characterised: unequal double cones, single cones (large and small) and rods. These show retinomotor movements where the rods elongate in the light and are masked by the pigment epithelium and contract in the dark as the pigment migrates sclerad. Ultrastructurally, 4 types of dark-staining (osmophilic) granules are described: (1) Small glycogen granules (0.033 &#181;m) aggregated at the bases of the photoreceptor nuclei and larger similar granules (0.078 &#181;m and termed paraboloids) vitread to the ellipsoid; (2) tapetal granules (0.32 &#181;m) distributed throughout the dorsal four-fifths of the retinal pigment epithelium (RPE); (3) pigment granules (0.5–2.0 &#181;m) in the RPE, concentrated in ventral retina; (4) granules or melanosomes (0.813 &#181;m) of the choriocapillaris. The second class of granules constitute a tapetum lucidum eliciting a yellow eyeshine when viewed in the dark. Two other tapeta also exist, a guanine tapetum (irregular guanine crystals) and a tapetum fibrosum (stacks of collagen fibrils). Functional correlations are made, and the putative ancestral (primitive) condition of particular visual characters is established for the ray-finned fishes by out-group comparisons.

THE TAPETUM FIBROSUM IN THE EYES OF TWO SMALL WHALES

AbtractThe pygmy sperm whale (Kogia breviceps) and the bottlenose dolphin (Tursiops truncatus) are equipped with a tapetum fibrosum and, with other Cetacea, are the only carnivores known to possess this typically ungulate tapetal type. Tapeta from two regions of a retina, each with a different spectral reflectance (blue and green), were found to have significantly different fibrillar diameters and inter‐fibrillar spacing. When the measured values are applied to a dielectric reflector model, the predicted wavelengths agree with the observed reflectance of the flat‐mounted tapeta. The spatial properties of the fibrils change progressively from the tapetal origin in the fibroblast layer to the pigment epithelium, suggesting that different wavelengths may be reflected systematically with tapetal depth. The very large number of reflecting layers characterizing these tapeta, relative to those of other carnivores, may provide for increased spectral purity and efficiency.

Fine Structure of the Choriocapillaris, Bruch's Membrane and Retinal Epithelium of the Cow

SummaryThe fine structure of the choriocapillaris, Bruch's membrane and retinal epithelium was investigated in both the tapetal and non‐tapetal fundus of the bovine eye. In ail locations the retinal epithelium consists of a single layer of cuboidal cells. The epithelial cells are joined laterally by apically located tight junctions and throughout the retina display numerous basal infoldings and fine apical processes which enclose rod outer segments. All retinal epithelial cells are rich in smooth endoplasmic reticulum and mitochondria and contain phagosomes. Although not as abundant, profiles of rough endoplasmic reticulum and polysomes are also noted in all locations. In non‐tapetal areas, melano‐somes are numerous whereas over the central tapetum fibrosum they are absent. The absence of melanosomes over a functional tapetum is to be expected. While lysosomes are present throughout the epithelial layer, over the tapetal region they appear to be more numerous. The apparent increase in lysosomal numbers in this location may indicate an enhanced shedding of outer segment material over the tapetum. Although some retinal epithelial cells are modified to accomodate a tapetum lucidum their morphology is basically similar throughout the retina and probably indicates that ail regions of the retinal epithelium are capable of the normal functions of this indispensible retinal layer. The choriocapillaris is heavily fenestrated on the border facing the retina and overlying the tapetum also displays fenestrae on its choroidal edge. Bruch's membrane (complexus basalis) is pentalaminate throughout the retina and is slightly thicker in the posterior fundus.

Fine structure of the bovine tapetum fibrosum.

SummaryThe fine structure of the tapetum lucidum of the domestic cow was studied by electron microscopy. In this ungulate the reflective layer is a tapetum fibrosum situated in the choroid and mainly restricted to the superior fundus. The tapetum is composed of a large array of fine extracellular collagen fibrils separated into lamellae by fibrocytes. The collagen fibrils display the normal cross‐striations of native collagen, are 0.2 μm in diameter and are arranged in a hexagonal pattern with a center‐to‐center spacing of about 0.2 μm. The diameter and spacing of these fibrils is consistent with the constructive interference of reflected light. A vascular lamella adjacent to the retinal epithelial layer contains the choriocapillaris and some irregularly arranged collagen fibrils. The tapetum is pierced by blood vessels which supply the choriocapillaris. Over the tapetum the retinal epithelium is non‐pigmented while in nontapetal regions this layer is pigmented. The choriocapillaris is not indented into the retinal epithelium as is the case in species with a tapetum cellulosum.

Electron microscopic observations on the retinal pigment epithelium and choroid in the domestic pig (Sus scrofa)

The morphology of the retinal pigment epithelium (RPE) and adjacent choroid has been investigated by electron microscopy in the domestic pig. The RPE consists of a single layer of cells which are columnar posteriorly but become cuboidal and even squamous moving peripherally in the fundus. The cells of the RPE layer regardless of location display basal (scleral) infoldings and apical (vitreal) processes and are joined laterally by junctional complexes. Throughout the retina the epithelial cells are rich in smooth endoplasmic reticulum and mitochondria but less so in rough endoplasmic reticulum and polysomes. The epithelial nucleus is vesicular and basally located. In the superior fundus an area of the RPE is very lightly pigmented and richer in lysosomes than is this layer in the inferior and peripheral fundus. The choroid overlying this area is also lightly pigmented and contains much collagen in a lamellar arrangement. This region may represent a vestigial tapetum fibrosum. Bruch's membrane is slightly thicker posteriorly but is everywhere seen to have a pentalaminate substructure. The choriocapillaris is a single layer of large capillaries which show numerous fenestrations facing the RPE. In the superior fundus the choriocapillaris is also highly fenestrated facing the choroid.

Morphology of the tapetum fibrosum in the eye of the domestic sheep

The fine structure of the tapetum lucidum of the domestic sheep was studied by both light and electron microscopy. In this species the reflective layer is a tapetum fibrosum situated in the choroid and restricted to the superior fundus. The tapetum is composed of a large array of fine extracellular collagen fibrils partially separated into lamellae 2–5 μm thick by fibrocytes. The collagen fibrils display the normal cross striations of native collagen, are 0.2 μm in diameter, and are arranged in a hexagonal pattern with a space of 0.2–0.25 μm between fibrils. The diameter and spacing of these fibrils is consistent with the constructive interference of reflected light. A vascular lamella adjacent to the retinal epithelium contains the choriocapillaris, pericytes, and irregularly arranged collagen fibrils. Over the tapetum the retinal epithelium is nonpigmented while in nontapetal regions it is pigmented. Bruch's membrane is pentalaminate in both tapetal and nontapetal regions.

Fine structure of the choriocapillaris, Bruch's membrane and retinal epithelium in the sheep.

The fine structure of the choriocapillaris, Bruch's membrane and retinal epithelium was investigated by light and electron microscopy in both the tapetal and non-tapetal fundus of the domestic sheep. The choriocapillaris are heavily fenestrated on the side facing the retina. Overlying the tapetum, the choriocapillaris also displays fenestrae on the choroidal border. Bruch's membrane is pentalaminate throughout the retina and slightly thicker over the tapetal region. In all locations the retinal epithelium consists of a single layer of cells, which vary in height depending upon their location. The epithelial cells are joined laterally by apically located tight junctions and throughout the retina display numerous basal infoldings and apical processes which enclose rod outer segments. The epithelial cell nucleus is large and vesicular. All retinal epithelial cells are rich in smooth endoplasmic reticulum and phagosomes. Although not as abundant, mitochondria, Golgi zones, profiles of rough endoplasmic reticulum and polysomes are also noted in all locations. In non-tapetal areas, melanosomes are numerous whereas over the central tapetum fibrosum they are absent. While lysosomes are present throughout the epithelial layer, over the tapetal area they appear to be more numerous. The absence of melanosomes over a functional tapetum fibrosum is to be expected. The apparent increase in lysosomal numbers in this location may indicate an enhanced shedding of outer segment material over the tapetal region. Although some retinal epithelial cells are modified to accommodate a tapetum lucidum their morphology is basically similar throughout the retina and probably indicates that all regions of the retinal epithelium are capable of the normal functions of this indispensible retinal layer.

Ultrastructural Observations on the Tapetum lucidum fibrosum

AbstractThe ultrastructural comparison made between the tapetum cellulosum of the cat and the tapetum fibrosum of the sheep has shown that the rods and the collagen fibrils have the same diameters and the same spatial arrangement.

THE ULTRASTRUCTURE OF BRUCH'S MEMBRANE. 3. THE MACULAR AREA OF THE HUMAN EYE.

Two previous reports in this series 1,2 described the fine structure of Bruch's membrane in the human, monkey, rabbit, guinea pig, and rat, 1 in the cat and dog which have a tapetum cellulosum, 2 and in the cow which has a tapetum fibrosum. 2 The fine structure of Bruch's membrane in the macular area of the human eye is described in this paper. The frequency of macular choroidal disease in humans prompted this special study. Materials and Methods The material studied consisted of four eyes of humans 60 years old or older. The eyes were enucleated because of ocular melanomas, but their macular areas were intact. The method of processing these eyes was described in the first paper of the series. 1 Pieces of choroid and attached retinal pigment epithelium were removed from the macular area by means of a trephine or razor blade and were then processed for

I. Contributions to the comparative anatomy of the mammalian eye, chiefly based on ophthalmoscopic examination

The colour of the Fundus oculi in animals devoid of a tapetum is mainly determined by reflection from the choroidal pigment. In animals possessing aTapetum cellulosum (Carnivores), the colour of the fundus is mainly determined by the colour of the retinal pigment. In animals which have a Tapetum fibrosum (Ungulates), the colour is determined by the structural colour of the tapetum modified by the colour of the retinal pigment. All the animals which I have examined may he considered as capable of being classified under one of three heads :— 1. The Red Type , including every shade of red, chocolate, brown, and grey. To this belong Man and all the Primates (with the exception of the Galagos and Loridoe); certain Insectivora; the Suricate and Cynictis, among the Carnivores; the Camelidae, Suidoe, Rhinoceros, and Hyracoidae among the Ungulates; all the Rodents (with the exception of Pteromys and the Spotted Cavy); the Edentata; the Marsupials (with the exception of the Virginian Opossum), and the Monotreme Echidna.