Biomedical subjects

M Davanger

Publications and source records attributed to M Davanger.

At least 19 recordsLinked to original sources

PubMed1992

The cumulative frequency distribution curve of the eye pressure.

Knowledge of the probability of having glaucoma at different levels of eye pressure is a prerequisite for estimating at which eye pressure levels preventive pressure-lowering treatment ought to be applied. The glaucoma tolerance may not be the same in all population groups. Calculation of tolerance distribution curves may be performed if the frequency distribution curves of pressure in eyes with and without glaucoma are known. Regression analysis has been performed to compute curves approaching the cumulative frequency distribution of the eye pressure in different subgroups. Results of a population study including subjects greater than or equal to 65 years of age have been used. An equation describing an asymmetric sigmoid curve has been applied in the curve fitting procedure. The derivative of this equation was used to describe the noncumulative frequency distribution curves. The analysis has been performed in subgroups consisting of normal eyes, glaucomatous eyes, eyes with and without pseudo-exfoliation.

Aged↗

PubMed1991

[EDP based medical records].

In our department we have begun to write our patients' medical history files in a computer data base. Each file is organized as a series of questions where it is possible to choose among several alternative answers instead of writing out each patient's history. We use a commercial software package modified to our specific needs. Statistical analysis of patients' files is included in the programme, to enable continuous quality control analysis of our performance.

Hospital Departments↗

PubMed1991

Electrondense cell inclusions of the human cone inner segments.

Electrondense cell inclusions resembling lysosomes are described in macular human cone inner segments. The organelles were regularly localized just outside the external limiting membrane, and only one or very few of them were present in each cell. For the first time it is shown that these organelles drain their content into the intercellular space between the photoreceptors.

Choroid Neoplasms↗

PubMed1991

The swelling of cornea in bank cultivation. The role of barriers and peripheral edge.

The swelling of a rabbit cornea in organ culture is caused by influx of fluid via the surface. Data regarding the weight increase rates during the first 4 h of corneal buttons with different diameters, have been used to calculate the net influx per mm2 per h via the anterior + posterior surfaces on one hand, and via the peripheral edge on the other hand. In fresh corneas the contribution to the corneal swelling, of the net fluid uptake via the anterior + the posterior surfaces, is negligible. The influx via the peripheral edge is about the same in fresh and freeze treated buttons. For freeze treated corneas, the resistance for fluid transport via the anterior + posterior surfaces seems to be 4 times higher than the resistance for transport via the peripheral edge. This result indicates that the Descemet's membrane and the Bowman's layer may have some barrier effect. An alternative or supplementary explanation is that, at least in swollen corneas, there may be reduced resistance to fluid flow along the corneal plane as compared with the flow vertical to this plane.

Animals↗

PubMed1991

The frequency distribution of the glaucoma tolerance limit.

The probability of having glaucoma may be expressed by the quotient p = (number of eyes with glaucomatous damage)/(total number of eyes). p has been calculated for different IOP levels, within a total population and also within groups with and without pseudo-exfoliation (PE). The resulting quotients were plotted versus IOP. Random irregularities were reduced by regression analysis, using the equation for the logistic distribution. The resulting sigmoid curves demonstrated that the probability p of having glaucomatous damage at a certain IOP is highest in the PE group. In the total material, the glaucoma probability p was 0.5 at IOP = 27.1 mmHg, and at IOP = 25.3 and 28.0 mmHg in the groups with and without PE, respectively. The frequency distributions of the glaucoma tolerance limit have been computed from the glaucoma probability curves.

Aged↗

PubMed1991

Frequency distribution of IOP. Analysis of a material using the gamma distribution.

The results of a population-based (age greater than or equal to 65 years) examination of the frequency distribution of IOP are reported. 3726 eyes in 1887 individuals were included in the examination. By consistent use of conventional, well-defined criteria, glaucoma was diagnosed in 6.4% of the individual eyes. In the total material, the average IOP was 18.0 mmHg. Average IOP was 28.7 mmHg in eyes with glaucomatous damage, vs 17.2 mmHg in the normal eyes. Variance of IOP was much higher in the glaucoma group as compared with the normal group. The IOP frequency distribution curve did not fit with a Gaussian curve; it was asymmetric, skewed to the right. The distribution curve obtained by plotting the recorded frequencies was disturbed by irrelevant irregularities, both random and systematic. The irregularities could be evened out by the application of regression analysis, using the equation for the gamma distribution. The IOP frequency distribution is well represented by a gamma distribution curve. The fit is improved by excluding eyes with extremely high and low IOP.

Aged↗

PubMed1991

The probability of having glaucoma at different IOP levels.

The probability of having glaucoma is indicated by the quotient (number of eyes with glaucoma)/(number of eyes in the total population). This quotient was calculated for each value of IOP. The number of eyes at each IOP value was taken from IOP frequency distribution curves for glaucomatous and normal eyes, calculated from values obtained by a population survey. By plotting the probability of having glaucoma vs IOP, a sigmoid curve was obtained. The curve indicates that while the glaucoma probability is near zero at IOP = 18 mmHg, it is 0.5 at 27-28 mmHg, and the probability approaches 1, i.e. certainty, at an IOP around 35 mmHg. The frequency distribution of the tolerance limit of IOP was calculated by derivation of this curve. The distribution of IOP tolerance limit was close to a normal distribution with average = 27.9 mmHg and standard deviation = 3.2 mmHg.

Aged↗

PubMed1991

Pseudo-exfoliation, IOP and glaucoma.

On the basis of a glaucoma survey in a total population greater than or equal to 65 years of age, the IOP in eyes with and without pseudo-exfoliation (PE) has been compared. The average IOP was 22.2 mmHg in eyes with PE versus 17.4 in eyes without. The corresponding averages in eyes without glaucomatous damage were 18.6 and 17.1 mmHg, and in eyes with glaucoma 31.5 and 25.5 mmHg. The IOP elevation connected with the PE process was 4.8, 1.5, and 6.0 mmHg in the total, normal and glaucomatous population, respectively. The IOP frequency distribution curves of these 3 groups were compared. The right shift of the distribution curves of the PE groups was more pronounced at high pressure levels. The PE process seems to elevate the IOP particularly in eyes with a high IOP, which is in correspondence with hydrodynamical laws. At a certain IOP, the probability of having glaucomatous damage was higher in eyes with PE than in those without, indicating an increased vulnerability of PE eyes to an elevated IOP. PE may be a glaucoma risk factor also on its own, i.e. independent of the pressure elevation connected with this syndrome.

Aged↗

PubMed1991

Migration of rabbit corneal endothelial cells on vitreous strands. An organ culture experiment.

Anterior vitreous synechia, sometimes seen as a complication after anterior segment surgery, has been mimicked in organ culture experiments. A specimen consisting of a cornea with a vitreous strand adhering to the posterior surface has been kept in culture medium for 6 and 12 days. Migration of corneal endothelial cells onto the surface of the vitreous strand started after 6 days, and the surface of the strand was partly or almost totally covered by corneal endothelium after 12 days. At this stage the cells were elongated and directed along the strand. In clinical situations a vitreous strand adhering to the cornea may exert traction on the retina. This traction may be caused by contraction of actin filaments in endothelial cells covering the strand. This experimental model may be used in attempts to modify the behaviour of the cells by pharmacological manipulation.

Animals↗

PubMed1990

Endothelial repair of posterior corneal wounds in rabbits. Influence of foetal calf serum in the culture medium.

UNLABELLED: The endothelial covering of experimental wounds on the posterior corneal surface has been studied in organ culture experiments. Defects involving the Descemet's membrane were produced, in addition to pure endothelial defects. The influence of foetal calf serum (FCS) on the healing process was examined. Wounds including the Descemet's membrane, about 1-2 X 3 mm, were not covered by cells after 12 days in FCS free medium. Such wounds were covered by endothelium after 6 days when cultivated in medium containing 10% FCS, and partly covered in 1% FCS. Pure endothelial defects, 4 mm in diameter, were cell-covered within 3-4 days irrespective of the presence of FCS. CONCLUSION: the presence of FCS is required for the healing of defects involving the Descemet's membrane, and not required for the healing of pure endothelial defects.

Animals↗

PubMed1990

In vitro endothelial healing of heat injuries of the posterior cornea in rabbits.

UNLABELLED: It was examined whether the healing promoting effect of Descemet's membrane on posterior corneal defects depends on heat labile molecules in the membrane. Localized thermal burns were produced by touching the posterior surface of rabbit corneas with a heated probe. This resulted in an endothelial defect, which was surrounded by a border of heat impaired, but living cells. The abnormal cells delayed the healing process by excerting contact inhibition on the surrounding undamaged endothelium. If the border of impaired cells was avoided by placing the 2 mm heat burn inside a 4 mm freeze erosion of the endothelium, the healing process was uninfluenced by the heat treatment. CONCLUSION: heat labile molecules in Descemet's membrane are not prerequisites for the healing promoting effect of the membrane on endothelial defects.

Animals↗

PubMed1989

Endothelial pump function in rabbit corneas kept under eye bank conditions.

Endothelial pump activity of rabbit corneas kept under eye bank conditions was examined. Different swelling rates for medium with and without ouabain were used for the calculation of endothelial pump rate. After an initial weight increase during 24 h, the control corneas kept approximately constant weight for 1 week. The ouabain-treated corneas increased continually, and during the time interval 24-48 h the increase was 41% of start weight. This corresponds to a pump activity of 2.3% of the weight of the normal corneal stroma per h, or to 9 microns of the corneal thickness per h. Each endothelial cell pumped fluid corresponding to 200-300% of the cell volume per h between day 1 (24 h) and day 8. The pump activity was gradually reduced after 8 days. The average weight was the same in both groups after 7 weeks.

Animals↗

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↗