Biomedical subjects

M Davanger

Publications and source records attributed to M Davanger.

At least 37 records · Page 2Linked to original sources

PubMed1989

Lateral cell connections at the inner segment level of human parafoveal photoreceptors.

Cytoplasmic processes on macular rod inner segments are described both in torn, fractured, and sectioned human tissue specimens. Longitudinal rows of villi are present along the inner segment's proximal part in fractured and sectioned tissue. Some villi were obviously abutting neighbouring cells. It is concluded that these processes undoubtedly represent a new type of cell extension different from calycal, pigment-epithelial, and Muller basket processes.

Fovea Centralis↗

PubMed1989

Low-pressure glaucoma and the concept of the IOP tolerance distribution curve.

Although glaucoma is considered to be caused by an elevated IOP, many eyes with an IOP within the normal range develop manifest glaucoma. The concept of an IOP tolerance distribution may clarify this paradox. The frequency of low-pressure glaucoma is a result of the constellation of the IOP distribution and the distribution of the IOP tolerance limit in the population. The low risk of glaucoma in the high normal IOP range is counteracted by the large number of eyes in this IOP range. It is possible to calculate the prevalence of glaucoma and the distribution of IOP in the untreated glaucoma population, resulting from different alternative distributions of IOP tolerance limit. Credible results were obtained by assuming a normal distribution of the IOP tolerance limit with an average = 26 mmHg and a standard deviation = 2.5 mmHg. In the development of glaucoma, the importance of the IOP relative to other factors, increases continually from low importance at low IOP to high importance at high IOP.

Glaucoma↗

PubMed1989

The cell barrier effect in rabbit corneas kept under eye bank conditions.

The influence of endothelial cell pumping and of cell barrier functions on cultivated corneas has been studied by comparing the rate of weight increase in freeze-treated, ouabain-treated and fresh corneas. Inhibition of the endothelial cell pump activity increased the swelling rate from 0.5% of start weight per h (fresh corneas) to about 2% per h (ouabain-treated corneas), as measured after 24 h in culture medium. The cell barrier effect was estimated by comparing the swelling rate of ouabain-treated corneas after 24 h, and the swelling rate of freeze-treated corneas with the same swelling pressure. The values are 2 and 9.5% per h, respectively. The swelling rate of freeze-treated corneas with different button diameters was found to increase with decreasing corneal button diameter.

Animals↗

PubMed1988

Swelling tendency of rabbit cornea in organ culture medium. Influence of button size.

The swelling tendency of fresh rabbit corneas kept in organ culture was determined by measuring percentage weight increase. Corneal buttons with diameters of 5, 9, 14, and 16 mm had an average weight increase during the first hour of 53%, 35%, 18%, and 8.6%, respectively. Those with diameter 5 and 9 mm had a continuous weight increase up to a maximum of 350% to 450% of start weight after 25 h and 57 h, respectively. Many corneas with 16 mm diameter (including a thin scleral rim) and some with 14 mm, had a temporary stable weight of average 56% (with an individual cornea stabilizing at only 15%) above start weight between day 2 to day 7. Thereafter a phase with approximately linear weight increase ended at a maximum weight of 350% to 450% of start weight after one month. It is concluded that the rate of corneal swelling in cultivation is highly dependent upon the corneal button size.

Animals↗

PubMed1987

Wound healing of rabbit cornea in organ culture.

A 2 mm perforating cut was made in the central part of 28 rabbit corneas. The corneas were then kept in organ culture from 3 h to 21 days. The healing process was studied by light microscopy and by transmission and scanning electron microscopy. The swelling of the corneal stroma adjacent to the wound created contact between the opposing wound edges within 3 h. Epithelial and endothelial cell migration into the wound was observed after 23 h. Penetration of cells through the perforation was avoided because the opposing wound edges were touching each other, thereby creating contact inhibition of cell proliferation. Cell cover of both the anterior and the posterior surface was completed within 3 days.

Animals↗

PubMed1986

Timolol and cornea.

The influence of timolol on the corneal epithelium and endothelium was studied in organ culture. The cell morphology was not influenced by drug concentrations less than or equal to 690 micrograms/ml. Cell death was observed at 6900 micrograms/ml. Endothelial cell proliferation after an experimental injury was slowed down at a drug concentration of 690 micrograms/ml. Injurious effects were not observed at the drug concentrations found in the aqueous humour by use of ophthalmic eye solution in eyes with a normal cornea. However, it may be indicated to use eye drops with reduced concentration of timolol in conditions facilitating the resorbtion of the drug.

Animals↗

PubMed1985

Influence of colchicine on the healing of corneal endothelium.

The healing of a corneal endothelial defect involves cell division and cell migration. Microtubuli form the spindle-fibers and parts of the cytoskeleton, and may therefore play a role in these cellular processes. In the present study colchicine is used in tissue culture to inhibit the assembly of microtubuli. Colchicine causes not only an arresting effect on cell division in the metaphase, but also an inhibitory effect on the cell migration. This latter effect is demonstrated by the radially directed, spindle-shaped cells seen in the repair zone of the control corneas being replaced by flat rounded cells. In this respect, in the presence of colchicine, the corneal endothelial cells behave like fibroblasts and not like epithelial cells.

Animals↗

PubMed1985

Experimental epithelial ingrowth. Epithelial/endothelial interaction through a corneal perforation, studied in organ culture.

The interaction of confronting corneal epithelium and endothelium has been studied by cultivation of corneas with open perforating wounds. In some experiments, the epithelium and the endothelium were initially damaged adjacent to the perforation, and the repair capacity was reduced by adding steroids or colchicine to the culture medium. The specimens were examined by scanning electron microscopy. The epithelium covered the stromal walls of the open perforation within 3 days. In most experiments, the epithelium and the endothelium met at the cut edge of Descemet's membrane, and this appeared to be a stable situation. However, if the endothelium was damaged and had reduced repair capacity, the epithelium invaded Descemet's membrane. The clinical implication is that the risk of epithelial ingrowth is present in eyes with a pathological endothelium.

Animals↗

PubMed1985

Aspects of the surface morphology of the corneal endothelium. An experimental study.

The influence on the surface of the corneal endothelial cells of 1) storage temperature of the enucleated eye, 2) epithelial abrasio, and 3) endothelial linear abrasio, has been examined. The surface structure may change rapidly following these procedures. The treatment of the cornea before fixation for electron microscopy should be standardized and as short as possible.

Animals↗

PubMed1985

The role of microfilaments in the healing of the corneal endothelium.

Actin microfilaments are presumed to play a role in cell locomotion. The function of these filaments may be selectively suppressed by cytochalasin. A dose-dependent delay of the repair of a corneal endothelial defect by the application of cytochalasin in tissue culture has been observed by SEM. This observation confirms that the actin microfilaments are important for the endothelial repair.

Animals↗

PubMed1985

The corneal endothelial cell interface.

The apical edges of corneal endothelial cells have been separated along lines forming a crisscross pattern, by the help of a special method of preparation. The visualization by SEM of the lateral faces of the cells is thereby made possible. The separation leads to the formation of thin strands spanning the gap between the apical edges of adjoining cells. They are formed by stretching of the normal apical flaps. This stretching demonstrates that the main intercellular adherence is located at the tips of the apical flaps. The basal edges of the endothelial cells can be inspected, and it can be seen that the basal face of the cells has and irregular form. Threadlike processes extend from the basal cell edges. They ascend in the intercellular space and make contact with the lateral face of the neighbouring cell at varying levels. These processes are presumed to mediate intercellular transfer.

Animals↗

PubMed1985

Changes in the rabbit corneal stroma caused by UV-radiation.

Three days after UV-irradiation of the rabbit cornea, there was epithelial loss and stromal oedema, which was most prominent in the anterior 1/4. Many of the keratocytes in this region were killed. The inner 3/4 of the stroma showed a large number of round or oval cells with nuclear fragmentation and abnormal inclusions. These cells were taken to be seriously, though reversibly harmed keratocytes. The tissue structure was normalized within one week, and the UV-induced changes seem to refer to the 290-350 nm interval.

Animals↗

PubMed1984

The healing of rabbit corneal endothelium.

A circular 4 mm endothelial defect was induced by transcorneal freezing. The experimental damage and the healing took place in the living rabbit in 15 eyes, and in the isolated cornea in organ culture in further 20 eyes. The reparative process was studied by SEM, and proved to be the same in vivo and in vitro. The defect was covered with endothelial cells after 3 days. The normal hexagonal pattern was regained after 3 weeks. Both cell migration and cell division were involved in the reparative process. Only cells recruited from a zone close to the defect were active; the cells situated more than a few cell diameters from the original edge maintained their form and size unchanged. The first phase of cell division was the formation of a spherical cell with numerous blebs on its surface.

Animals↗

PubMed1984

The healing of human corneal endothelium. An in vitro study.

A 4 mm circular defect was made on the endothelium by transcorneal freezing of 5 normal human corneas. The eyes were enucleated because of malignant tumours, patient age 3 to 74 years. After excision, the corneas were kept in culture medium for 3 (4) days, and subsequently prepared for SEM. At this stage, the defect was covered with endothelium, whose origin was a narrow zone adjoining the edge of the defect. The endothelium on the peripheral, undamaged part of the cornea did not seem to take part in the repair process, neither by proliferation, enlargement nor by migration. Dividing cells were found scattered on the damaged area. The repair process was found to be similar in all five eyes, irrespective of the age of the patient. In organ culture, the healing of corneal endothelial defects is similar in rabbits and in humans.

Adult↗

PubMed1984

The effect of steroids on the healing of the corneal endothelium. An in vivo and in vitro study in rabbits.

The effect of steroids on the repair of a corneal endothelial defect in rabbits was studied by in vivo and by organ culture experiments. A standard 4 mm defect was produced by transcorneal freezing. The situation after 2, 3, and 4 days was studied by scanning electron microscopy. Preliminary experiments demonstrated that topical eye treatment influenced on the repair process of the untreated, contralateral eye. The preservants of commercial eye drops caused delayed healing in organ culture. These effects were excluded from the control experiments. Topical eye treatment with steroid eye drops for 3 days caused a one day delay in the repair process. In culture medium, delayed repair was found at hydrocortisone concentrations greater than or equal to 0.125 mg/ml. The visible influence of hydrocortisone increased with the concentration in the range examined, between 0.05 mg/ml and 1 mg/ml.

Administration, Topical↗

PubMed1984

On the spatial organization of the cornea endothelium.

A hexagonal pattern is formed by the apical aspects of the corneal endothelial cells. However, by electron microscopy of surface-parallel sections it can be seen that the basal part of these cells has a highly irregular shape with deep indentations and high ridges. Near the Descemet membrane numerous cytoplasmic processes are tangled together in a bewildering pattern. A few of these processes are exposed to the posterior surface, where they may be seen as small cell-like areas delineated by cell borders. The hexagonal apical pattern of the endothelium is related to minimum total length of the intercellular apical sealing. This pattern may develop by a minimizing process with analogy to the minimum surface formation of soap bubble film.

Animals↗

PubMed1984

A new method of determining the cell density from a corneal specular micrograph.

Non-contact specular micrographs of the corneal endothelium are usually only a few cell diameters in width. The oblong shape leads to uncertainties in the determination of cell density by counting the number of cells on an area of known size. A new method, particularly suited for a long and narrow picture, is described. A line with a length corresponding to 1 mm is drawn on a specular micrograph. The number n of cells sectioned by this line is counted. It is demonstrated that the average cell size A may be determined from n by the formula A = 1 404 669/n2 micron2. The relation between A and n is presented in Table 1, which also gives the corresponding cell density expressed by the number of cells per mm2.

Animals↗

PubMed1982

Surface morphology of explants from the human retinal pigment epithelium in culture. A scanning electron microscopic study.

The alterations in surface morphology in human retinal pigment epithelium in explant culture was studied by scanning electron microscopy. After 14 days in culture, large areas of the epithelium showed well preserved surface villi. In some zones, however, the density of the finger-like villi were reduced and the shorter villi became more visible. The short villi are lamellar in structure and constitute systems of communicating membranous folds and not isolated structures as previously believed. Most of the tall finger-like villi were found to have their bases on the top of these folds. Dead cells followed 2 different pathways of degeneration. Some showed large ruptures in the membrane, followed by expulsion of organelles and finally detachment of the cell from Bruch's membrane. With other cells, a progressive disintegration of the cell membrane was observed. The first type of degeneration occurred most frequently in dilated, single cells, whereas the latter type was found in larger areas of necrosis.

Cell Membrane↗