Studies on the eyes of gars (Lepisosteidae) with special reference to the tapetum lucidum

1973 ◽  
Vol 51 (5) ◽  
pp. 501-508 ◽  
Author(s):  
J. A. C. Nicol ◽  
H. J. Arnott
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Visible Spectrum ◽  
Tapetum Lucidum ◽  
Tubular System ◽  
Noteworthy Feature ◽  
Membrane Bound ◽  
Dim Light ◽  
Ammoniacal Silver ◽  
Pigment Epithelial Cells

Eyes of gars (Lepisosteus) possess a yellow tapetum lucidum which is located in processes of the pigment epithelium. A yellow reflecting pigment is involved, enclosed in tapetal spheres each about 240 nm in diameter. Retinomotor movements take place: in darkness (or dim light) the black retinal pigment retracts, exposing the tapetum, and the rods shorten; in the light the pigment migrates inwards, obscuring the tapetum, and the rods elongate. The tapetal pigment is soluble in water, dilute acid, and alkali, and insoluble in organic solvents; it is rendered insoluble (to water) by heavy metals; and it stains with reagents used to visualize phenolic compounds (ferric–ferricyanide; ammoniacal silver nitrate). A method of extracting the pigment is described, and the ultraviolet/visible spectrum shown. The refractive index is high (n23 1.59) and that, in conjunction with the size and arrangement of the tapetal spheres, is conducive to backscatter. A second noteworthy feature of the pigment epithelial cells is the presence of an extensive Golgi apparatus consisting of many dictyosomes interconnected by a complicated tubular system of smooth membranes. The tubules exhibit periodic swellings or vesiculations in which the tapetal spheres individually are formed. Comparisons are made with a similar Golgi complex in Styela, and with membrane-bound vesicles, derived from Golgi and concerned with formation of ommochrome granules, in Drosophila.

Studies on the eyes of catfishes with special reference to the tapetum lucidum

1974 ◽  
Vol 186 (1082) ◽  
pp. 13-36 ◽  
Keyword(s):  
Ictalurus Punctatus ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Single Layer ◽  
High Refractive Index ◽  
Extensive Study ◽  
Rods And Cones ◽  
Light Yellow ◽  
Membrane Bound ◽  
Pigment Epithelial Cells

Marine catfishes (Ariidae) and freshwater catfishes (Ictaluridae) have ocular tapeta lucida. Species examined were Bagre marinus (Mitchill), Arius felis (L.), Ictalurus punctatus (Rafinesque), I. natalis (Lesueur), I. nebulosus (Lesueur) and Pylodictis olivaris (Rafinesque). The tapeta are white reflectors located in the pigment epithelium; they occupy most of the fundus except for a narrow black ventral field. A more extensive study was made of the tapetum of the hardhead catfish A. felis . In histologic sections the tapetum is yellow brown and is easily confused with retinal pigment. It can be distinguished because it stains with ferric-ferricyanide and dissolves in methanol-hydrochloric acid after Carnoy fixation. The tapetum is occluded by melanosomes which move inwards in light, and it is exposed by movement outwards of melanosomes in dim light or darkness. Electron microscopy shows that processes of the pigment epithelial cells contain many membrane-bound tapetal spheres which enclose the tapetal pigment and are responsible for reflexion of light. Spheres are 370 nm in diameter (average); there are about 5.5 spheres in 1 μm 3 , and the tapetum is about 90 μm thick. Rods and cones are equal in number; rods form a single layer, cones are single and possess an accessory outer segment. Transmission of the tapetum is minimal at short wavelengths and rises steadily above 500 nm. Reflectance is diffuse; it rises to a maximum at 500 nm, and is high at long wavelengths. The tapetum has a high refractive index, ca . 1.56, favouring light scattering. Some characteristics of the extracted tapetal pigment are pre­sented: it is light yellow, and absorbance maxima occur at 260 and 330 nm in acidic meth­anol. The pigment epithelium contains lysosome-like bodies but no myeloid bodies. The hardhead retina contains a visual pigment 527 2 . Measurements of natural light (irradiance) in coastal waters inhabited by sea catfishes are presented: the waters are turbid and transmit maximally at 575 to 580 nm. The findings, in relation to earlier work on the catfish eye, performance of the eye and habits of the fish are discussed.

Retinol dehydrogenases: Membrane-bound enzymes for the visual function

2014 ◽  
Vol 92 (6) ◽  
pp. 510-523 ◽  
Author(s):  
Mustapha Lhor ◽  
Christian Salesse
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Membrane Binding ◽  
Large Family ◽  
Structural Features ◽  
Visual Cycle ◽  
Retinoid Metabolism ◽  
Current State ◽  
Membrane Bound ◽  
Membrane Bound Enzymes

Retinoid metabolism is important for many physiological functions, such as differenciation, growth, and vision. In the visual context, after the absorption of light in rod photoreceptors by the visual pigment rhodopsin, 11-cis retinal is isomerized to all-trans retinal. This retinoid subsequently undergoes a series of modifications during the visual cycle through a cascade of reactions occurring in photoreceptors and in the retinal pigment epithelium. Retinol dehydrogenases (RDHs) are enzymes responsible for crucial steps of this visual cycle. They belong to a large family of proteins designated as short-chain dehydrogenases/reductases. The structure of these RDHs has been predicted using modern bioinformatics tools, which allowed to propose models with similar structures including a common Rossman fold. These enzymes undergo oxidoreduction reactions, whose direction is dictated by the preference and concentration of their individual cofactor (NAD(H)/NADP(H)). This review presents the current state of knowledge on functional and structural features of RDHs involved in the visual cycle as well as knockout models. RDHs are described as integral or peripheral enzymes. A topology model of the membrane binding of these RDHs via their N- and (or) C-terminal domain has been proposed on the basis of their individual properties. Membrane binding is a crucial issue for these enzymes because of the high hydrophobicity of their retinoid substrates.

scholarly journals Fine structure of the retinal pigment epithelium and cones of Antarctic fish Notohenia coriiceps Richardson in light and dark-conditions

2007 ◽  
Vol 24 (1) ◽  
pp. 33-40 ◽  
Author(s):  
Lucélia Donatti ◽  
Edith Fanta
Keyword(s):  
Epithelial Cells ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Antarctic Fish ◽  
Basal Region ◽  
Dense Cytoplasm ◽  
Transmission Electron ◽  
Notothenia Coriiceps ◽  
The Antarctic ◽  
Pigment Epithelial Cells

The Antarctic fish Notothenia coriiceps Richardson, 1844 lives in an environment of daily and annual photic variation and retina cells have to adjust morphologically to environmental luminosity. After seven day dark or seven day light acclimation of two groups of fish, retinas were extracted and processed for light and transmission electron microscopy. In seven day dark adapted, retina pigment epithelium melanin granules were aggregated at the basal region of cells, and macrophages were seen adjacent to the apical microvilli, between the photoreceptors. In seven day light adapted epithelium, melanin granules were inside the apical microvilli of epithelial cells and macrophages were absent. The supranuclear region of cones adapted to seven day light had less electron dense cytoplasm, and an endoplasmic reticulum with broad tubules. The mitochondria in the internal segment of cones adapted to seven day light were larger, and less electron dense. The differences in the morphology of cones and pigment epithelial cells indicate that N. coriiceps has retinal structural adjustments presumably optimizing vision in different light conditions.

Carbonic Anhydrase Inhibitor with Topical NSAID Therapy to Manage Cystoid Macular Edema in a Case of Gyrate Atrophy

2017 ◽  
Vol 27 (6) ◽  
pp. e179-e183 ◽  
Author(s):  
Elena Piozzi ◽  
Salvatore Alessi ◽  
Silvia Santambrogio ◽  
Giovanni Cillino ◽  
Marco Mazza ◽  
...  
Keyword(s):  
Carbonic Anhydrase ◽  
Macular Edema ◽  
Cystoid Macular Edema ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Carbonic Anhydrase Inhibitor ◽  
Gyrate Atrophy ◽  
First Case ◽  
Membrane Bound ◽  
Inflammatory Drugs

Purpose Gyrate atrophy of the choroid and retina (GACR) is a rare chorioretinal dystrophy characterized by a deficiency of the enzyme ornithine aminotransferase, inherited in an autosomal recessive pattern. Case Report We report a case of a 17-year-old girl with GACR, for whom the level of serum ornithine had been reduced by an arginine-restricted diet. The patient was responsive to an association of topical nonsteroidal anti-inflammatory drugs (NSAIDs) and a carbonic anhydrase inhibitor (CAI) to reduce cystoid macular edema (CME). Conclusions The efficacy of topical NSAIDs and systemic CAI association indicates that the imbalance in the distribution of retinal pigment epithelium membrane-bound carbonic anhydrase could play a major role in CME pathogenesis in GACR. To our knowledge, this is the first case of therapy with CAI treatment for GACR-related CME.

Studies on the eyes of bigeyes (Teleostei Priacanthidae) with special reference to the tapetum lucidum

1980 ◽  
Vol 210 (1181) ◽  
pp. 499-512 ◽  
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Red Light ◽  
Broad Band ◽  
Constructive Interference ◽  
Retinal Surface ◽  
Rods And Cones ◽  
Quarter Wavelength ◽  
Tapetum Lucidum

Eyes of glasseyes (Priacanthidae) show conspicuous eyeshine and have a brilliant tapetum in the chorioid. The tapetum underlies the entire retina; it is composed of several rows of reflecting cells which contain stacks of flat crystals lying parallel to the retinal surface in the central fundus and obliquely towards the periphery. Reflexion is orange and specular; the reflexion spectrum is a broad band centred at about 630 nm. Processes of the pigment epithelium contain black pigment in some parts of the eye; pigment is especially dense in a horizontal central band and in the lower field, but is absent from the cell bases. The ultrastructure of the pigment epithelium and of the tapetum is described. The crystals and intervening cytoplasmic lamellae are organized as quarter-wavelength films to give maximal reflexion of long wavelengths (orange and red light) by constructive interference. Rods and cones are present; there is no retinomotor activity. The mechanism of reflexion, efficiency of the tapetum and role of the retinal pigment are discussed.

scholarly journals HEREDITARY MACULAR DYSTROPHIES. PART 1. DYSTROPHIES ASSOCIATED WITH DYSFUNCTION OF RETINAL PIGMENT EPITHELIAL CELLS

2018 ◽  
Vol 13 (2) ◽  
pp. 103-108
Author(s):  
L. A Katargina ◽  
E. V Denisova ◽  
Natal’ja A. Osipova
Keyword(s):  
Differential Diagnosis ◽  
Retinal Pigment Epithelium ◽  
Retinal Pigment Epithelial ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Retinal Pigment Epithelial Cells ◽  
Review Of The Literature ◽  
Pigment Epithelial ◽  
Medical Articles ◽  
Pigment Epithelial Cells

Purpose - to acquaint the reader with a relatively rare heterogeneous group of diseases - hereditary macular dystrophies associated with damage to cells of retinal pigment epithelium and external segments of photoreceptors. А review of the literature based on publications from the Medline scientific medical articles database is presented. The review includes a description of the clinical picture, consideration of diagnosis and differential diagnosis of the main juvenile macular dystrophies, illustrated by own clinical examples.

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