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Biomedical subjects

M Davanger

Publications and source records attributed to M Davanger.

At least 55 records · Page 3Linked to original sources
PubMed1982

Changes of the cornea endothelium after ultraviolet radiation.

The rabbit cornea endothelium has been studied with specular and scanning electron microscopy after exposure with a commercially available ultraviolet lamp. The animals were plased 50 cm from the source, and most experiments were run with a 20 min exposure time. In the specular microscope, the endothelium revealed numerous circumscript reflex-free areas, which were observed from 4 days up to 8 months after the irradiation. A wide variety of changes were found in the scanning electron microscope. One day after the exposure the cells showed indistinct outlines, and they were bulging into the anterior chamber. In some regions the pattern was dominated by marked grooves preferentially along the cell demarcations, whereas other regions showed rough surfaced cells because of cytoplasmic projections and grainy deposits. At the 3 days stage there was a marked pleomorphy, and some cells were on their way to being rejected. After one week the cobblestone appearance of the endothelium was about to decline. Partly rejected cells were still common. In addition, distinct, ringshaped local impressions occurred imitating the previous described grooves. This phenomenon along with some single endothelial cells studied with microvilli were the abnormal findings 8 months after the damage. It is concluded that although ultraviolet radiation is largely absorbed in the cornea, the threshold dose for damage of the endothelium is not beyond those used for practical purpose. The endothelium was surprisingly resistant towards repeated radiation damage.

Animals↗
PubMed1981

Iris neovascularisation in eyes with pseudoexfoliation syndrome.

The iris vascular bed of eyes with pseudoexfoliation syndrome has been studied with electron microscopy. Two of the eyes suffered from painful glaucoma, whereas the third showed normal intraocular pressure. The following changes were observed: (1) deposits of pseudoexfoliation material lying adjacent to the endothelial wall; (2) thin vessel basement membrane, sometimes even interrupted; (3) extreme reduction of vessel lumina through increased volume of the endothelial cells; (4) fenestration of the endothelial wall. It is suggested that the iris neovascularisation in eyes with pseudoexfoliation syndrome is due to an obstruction of iris vessels causing tissue hypoxia.

Aged↗
PubMed1980

Pseudo-exfoliation material. Electron microscopy after the application of lanthanum as tracer particles and ionic stain.

Lenses with pseudo-exfoliation (PE) were suspended in a solution of lanthanum, which was present partly in ionic form, partly as electron-dense tracer particles in colloidal solution, dependent on pH and on the concentration of lanthanum. By electron microscopy the tracer particles were found in a narrow zone along the surface of the PE excrescences. Only a few of the smallest particles had penetrated into their most superficial layer. In the specimens treated with ionic lanthanum, the effect was an electron-dense staining of the PE material within a 1-2 micrometer thick superficial layer. The PE fibrils as well as parts of the interfibrillar spaces were stained. These results indicate the presence of proteoglycans, and confirm the concept of an interfibrillar matrix which excludes other macromolecules and particles from penetrating into the material.

Cataract↗
PubMed1980

On the ultrastructure and the formation of pseudo-exfoliation material.

Pseudo-exfoliation (PE) excrescences on the anterior lens surface were studied by electron microscopy. In some cases the superficial layer of the excrescences consisted of a meshwork of fibrils and filamentous subfibrillar units. It could be clearly seen that the fibrils were formed by lateral aggregation of filamentous units. Both the filaments and the fibrils had crossbands regularly spaced at 17 nm. In some fibrils, every third crossband was fainter than their neighbouring crossbands. Thereby a secondary periodicity appeared, the new period consisting of three crossbands in the order dense-faint-dense. The length of this period was 17 x 3 = 51 nm, i.e. the same as the distance between the crossbands of conventional PE fibrils. All transitional forms between the fibrils with 17 nm periodicity and the conventional PE fibrils were found, and there was a gradual transition between the material described and conventional PE material. It is suggested that the material on the surface of the PE excrescences represent newly formed PE material. This may be formed by condensation and linear polymerization of two kinds of units, corresponding to the dense and the faint crossbands.

Cataract↗
PubMed1979

Villous processes from the inner segments of cones in the human macula lutea.

The cones of the human macula lutea were examined by scanning electron microscopy. It was found that each inner segment had about 15 thread-like processes which projected from the cell surface. They were arranged in a longitudinal straight line along the photoreceptor, and were directed away from or towards the fovea contralis. The villous processes may be analogous with the lateral fins of the inner segments of certain vertebrates. They may perhaps bridge the space between neighbouring photoreceptors and may establish contact and interaction between them.

Adult↗
PubMed1978

Studies on the pseudo-exfoliation material: a review.

Pseudo-exfoliation (PE) material may be found on several surfaces of the anterior segment of the eye. The material contains typical cross-banded PE fibrils distributed at random. These fibrils have been studied with transmission and scanning electron microscopy. Negative staining of dispersed PE fibrils indicated that the fibrils have a core consisting of a small number of filamentous subunits. The core is surrounded by a fuzzy material which protrudes from the fibrils at regular intervals. This is the basis of the cross-bands of the fibrils. Staining with ruthenium red and alcian blue indicates that glycosaminoglycans are present, mainly on the surface of the PE fibrils. Tracer particles have been applied in vitro on lenses with PE. The distribution of the tracers in the PE material indicates that the fibrils are embedded in an interfibrillar matrix consisting of filamentous units. It is concluded that the PE material is made up of filamentous proteo-glycosaminoglycans. The fibrils represent relatively dense aggregates of such filaments, while the interfibrillar matrix is a gel of the same filamentous units in a loose, random arrangement.

Eye Diseases↗
PubMed1978

A note on the pseudo-exfoliation fibrils.

Both transmission (TEM) and scanning electron microscopy (SEM) demonstrate that typical fibrils are the dominant feature of the pseudo-exfoliation (PE) material. The purpose of this work has been to examine whether the TEM and the SEM fibrils are identical, and to determine to which extent the morphology of the PE material is changed during the preparation for SEM, especially by the drying procedure. Specimens from lenses with PE, which had beforehand been prepared for and examined by SEM, were embedded, sectioned and examined by TEM. The results indicate that, as far as it can be seen by this method, the changes induced in the PE material by the drying procedure are not substanial. The TEM and the SEM fibrils are identical.

Cataract↗
PubMed1978

The ciliary body and the suspension of the lens in rabbits. A scanning electron microscopy study.

The ciliary body in rabbits is dominated by the ciliary processes, which number about 165. Most of them are straight, regularly spaced and uniformly shaped, and they have an even surface when seen at low magnification. They are separated by deep valleys with almost vertical sides. Anteriorly, the ciliary processes end abruptly, and about every second process leads into an iridial process which run radially along the posterior surface of the iris. At higher magnification, the individual cells can be seen to be demarcated by furrows, with a pattern which is specific for the different parts of the surfaces studied. The lens is suspended in innumerable zonular fibers, forming a rather thick mat. They attach in one continuous belt at the anterior end of the ciliary processes, and directly on the lens equator. The anatomy of this part the rabbit eye differs in many respects from that found in primates.

Animals↗
PubMed1978

Pseudo-exfoliation fibrils examined by negative staining.

Pseudo-exfoliation (PE) material, collected from lenses extracted because of cataract, has been examined by negative staining. The material was fragmented by ultrasound into single fibrils and small collections of fibrils. The fibrils were composed of a small number of filamentous subunits associated with or surrounded by a fuzzy material which had side excrescences at regular intervals of 50--55 nm or 25--30 nm. The side excrescences correspond to the cross-bands of the PE fibrils. It is proposed that the PE fibrils are composed of a few subunits of a fibrillar protein, which form a core to which glycosaminoglycan side chains are attached. The visible periodicity of the PE fibrils, appearing as cross-bands, is thought to be caused by clusters of glycosaminoglycan distributed at regular intervals along the fibrils.

Cytoskeleton↗
PubMed1978

On the interfibrillar matrix of the pseudo-exfoliation material.

Lenses with pseudo-exfoliation (PE) were suspended in a 10% solution of ferritin. In order to retain ferritin at the surface of the PE material during the preparation for the subsequent transmission electron microscopy, some of the lenses were coated with a thin layer of gelatin before the application of the ferritin solution. It was found that ferritin particles to a certain extent penetrated into the PE material. But the concentration of ferritin was much higher in the gelatin coating than in the PE material. The concentration changed stepwise at the interface between the gelatin and the PE material. The ferritin particles in the PE material were mainly found adjacent to the PE fibrils, and there was a certain tendency towards a linear arrangement of the particles. In some specimens, in which thin filaments were found in the interfibrillar space, the ferritin was found mainly along these filaments. The results are interpreted in light of earlier works in which other tracers have been applied. The marked lower concentration of ferritin in the PE material than in the gelatin coating, and the stepwise fall in concentration at the interface between the two materials, seem to confirm the presence of an interfibrillar matrix of the PE material.

Cytoskeleton↗
PubMed1978

The ciliary body and the iris in experimental uveitis in rabbits. A scanning electron microscopic study.

Acute anterior immunogenic uveitis of varying degree was induced in rabbits by the injection of human serum albumin into the vitreous body. After fixation and drying by the critical point method, the lens, the zonules, the vitreous and, in some specimens, coagulated exudate were removed by careful dissection. The surface of the ciliary body and the posterior surface of the iris were examined by scanning electron microscopy. In moderate uveitis, the ciliary body was covered by a thin layer of leucocytes enmeshed in fibrin strands. Scattered deposits of fibrin and a few leucocytes were also found in the iris. In severe uveitis, the processes of the ciliary body had nearly disappeared because of oedema and exudate, which also contained erythrocytes. The numerous leucocytes had marked excrescences formed by folds of the cell membrane. Fibrin seemed to play a role in the attachment of the leucocytes on the surface of the ciliary body.

Acute Disease↗
PubMed1977

On the molecular composition and physico-chemical properties of the pseudo-exfoliation material.

The protein tracer peroxidase has been found to be excluded from pseudoexfoliation (PE) material. But after the treatment of the PE material with cetylpyridinium-chloride, peroxidase was found to penetrate into the material. This observation seems to support the concept that the PE material is a gel of proteoglycans, from which peroxidase is excluded by an excluded volume effect. Microperoxidase was found to penetrate into the superficial parts of the (untreated) PE material, and to be regularly distributed according to two different patterns: 1) along the PE fibrils, and 2) along lines in the interfibrillar matrix; lines which can not be seen without the presence of microperoxidase. At both locations the microperoxidase reaction product was found at regular intervals, with spacings of about 53 nm. The interpretation is that both the fibrils and the interfibrillar matrix are composed of the same kind of long extended linear proteoglycan complexes, but with a different arrangement and density.

Eye Diseases↗
PubMed1977

A method of isolating and collecting pseudo-exfoliation material from extracted cataractous lenses.

It has been observed that the pseudo-exfoliation (PE) material on the surface of extracted lenses was not dissolved by a papain solution, while the underlying lens capsule was digested. This forms the basis of a method for isolating and collecting PE material. The anterior lens surface was swept with a cilium after the lens had been suspended in a 5% papain solution for 1/2-1 hour. The PE material was loosened in flakes which adhered to the tip of the cilium and could be collected as a lump. By light and scanning and transmission electron microscopy no contaminants could be seen, and no damage to the PE material was disclosed.

Ciliary Body↗
PubMed1977

The ciliary body and the suspension of the lens in a monkey (Cercopithecus aethiops). A scanning electron microscopic study.

The zonules of Zinn and their insertion on the ciliary body and the lens in a monkey (Cercopithecus aethiops) have been studied with the scanning electron microscope. The specimens were dissected after drying by the critical point method, and the lens was separated from the ciliary body by simple traction. The pars plana was completely covered by a mat which consisted of meridionally directed zonule-like fibers. Most of these fibers inserted at the base of the posterior end of the ciliary processes, and some of them radiated into the valleys between the processes. About two fibers for each process split off from the mat and became attached to the sides of the processes near their posterior ends. The true zonules spanned from the sides of the processes to the pre- and post-equatorial region of the lens. They were clearly separated into an anterior and a posterior row with no fibers crossing over from one row to the other. Usually four true zonules joined each process, i.e. one zonule of the anterior row and one of the posterior row attached to each side of the single ciliary process.

Animals↗
PubMed1977

Notes on the distribution of pseudo-exfoliation material with particular reference to the uveoscleral route of aqueous humour.

The distribution of pseudo-exfoliation material along the uveoscleral route of aqueous humour has been studied by electron microscopy. It turned out that such material is present only in the very first part of this exit pathway, i.e. in the innermost zone of the connective tissue bordering the anterior chamber angle. No pseudo-exfoliation material was observed between the ciliary muscle cells, in the suprachoroidal space or in the sclera. It is concluded that transport of pseudo-exfoliation material by flow of aqueous humour through the uveoscleral route to the bulbar and palpebral conjunctiva is improbable, and accordingly the pseudo-exfoliation material found in extrascleral tissue most likely arises in loco.

Aged↗
PubMed1975

The pseudo-exfoliation syndrome. A scanning electron microscopic study. I. The anterior lens surface.

The distribution and the surface of pseudo-exfoliation (PE) material on the anterior lens surface has been studied by scanning electron microscopy. The lenses were fixed in glutaraldehyde and OsO4, and dried by the critical point method. The PE granules of ther peripheral band may rest upon a basal lamella, which may terminate in a sharp edge bordering the intermediate zone. The basal lamella may continue peripherally beyond the granular peripheral band, towards the lens equator, where the basal lamella may cover the zonular attachment zone. The central disc is considered to be analogous to this lamella. In high magnification it is found that the surface of the granular and the lamellar PE material is formed by an irregular meshwork of tortuous fibrils, which may be coiled as spirals. The diameter of the fibrils is between 500 and 1000 A, and their length may be up to 5 mum. The possibility that these fibrils are a condensation product of mucopolysaccharides is discussed.

Eye Diseases↗
PubMed1975

The pseudo-exfoliation syndrome. A scanning electron microscopic study. II. The posterior chamber region.

The distribution of pseudo-exfoliation (PE) material as well as the finer details of its surface has been studied by scanning electron microscopy on the surfaces facing the posterior chamber. The specimens were fixed in glutaraldehyde and OSO4 and dried by the critical point method, after careful dissection of the anterior hyaloid surface. Granules and plaques of PE material were found to attach to the iris, to the ridges of the ciliary processes, to the zonules, and along radial stripes on the anterior hyaloid surface, one for each zonule touching this surface. It seems as if the PE material is located mainly on sites on contact between two surfaces. In high mangnification it is found that the surface of the PE material is formed by an irregular meshwork of fibrils, the diameter of which is about 550-700 A. The fibrils are characteristically coiled, partly into regular spirals. The hypothesis is put forward that these fibrils are formed by a condensation of mucopolysaccharides forming the ground substance of the PE material.

Ciliary Body↗