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Biomedical subjects

A Ringvold

Publications and source records attributed to A Ringvold.

At least 37 records · Page 2Linked to original sources
PubMed1995

Quenching of UV-induced fluorescence by ascorbic acid in the aqueous humour.

Spectrophotometry and spectrofluorimetry of bovine aqueous humour have been performed. The question of whether mechanisms for fluorescence quenching exist in the eye media was evaluated. It turned out that the marked fluorescence of tryptophane and protein was considerably quenched by the ascorbic acid, an observation not shown before. Thus, the aqueous humour minimizes UV-radiation to the lens in diurnal animals through three different mechanisms: 1) Absorption. 2) Fluorescence-quenching. 3) Fluorescence-mediated ray transformation of energy-rich short wavelengths to less potent longer wave-lengths. The impact of each of them is significantly influenced by the ascorbate concentration in the aqueous humour. The phenomenon of fluorescence-mediated ray transformation is, of course, per se independent of ascorbate, but the transformational input is significantly reduced due to ascorbate.

Absorption↗
PubMed1993

[Acute eye problems].

The article reviews diagnostic and therapeutic problems in connection with patients with "acute eye". Usually the person visits the doctor for one of the following reasons: Sudden change in vision A red and perhaps painful eye Injury to the eye.

Acute Disease↗
PubMed1993

The middle-Norway eye-screening study. III. The prevalence of capsular glaucoma is influenced by blood-group antigens.

The association between blood groups (ABO, Rh, Kell, Duffy) and pseudo-exfoliation syndrome, simple, and capsular glaucoma have been evaluated. The findings were: 1). No statistically significant abnormalities regarding blood group distribution in persons with pseudo-exfoliation syndrome. 2). In contrast to simple glaucoma, capsular glaucoma showed an abnormal distribution in the ABO- and the Kell-system. There was less glaucoma prevalence in the capsular A1-group compared to the O-group (p = 0.013), and less in the K1 negative group compared to the K1 positive one (p = 0.005). This trend was even escalated when combining the two systems: Among the K1 negative persons the glaucoma prevalence was lower in the A1-group compared to the O-group (p = 0.003). In the K1 negative group only 9 of 61 A1-persons developed glaucoma, in contrast to the K1 positive group where 4 of 4 A1-persons had glaucoma. This difference gave p < or = 0.00038, whereas the corresponding difference for the O-groups showed p = 0.65. It is concluded that once a person with blood group A1 has developed pseudo-exfoliation syndrome, the risk that capsular glaucoma will occur is about 7 times higher when that person is K1 positive compared to K1 negative. Perhaps this observation may be used as a prognostic factor for non-glaucomatous PE positive persons.

Aged↗
PubMed1992

Dose response and duration of action of dorzolamide, a topical carbonic anhydrase inhibitor.

The multiple-dose, dose-response relationship and duration of action of the novel topical carbonic anhydrase inhibitor dorzolamide (previously known as MK-507) were investigated in a double-masked, randomized, placebo-controlled, parallel study in 73 patients with bilateral primary open angle glaucoma or ocular hypertension. Dorzolamide (0.7%, 1.4%, or 2%) or placebo was administered every 12 hours for 5 days and then every 8 hours for 7 days. Intraocular pressure was investigated with multiple 12-hour diurnal curves. All concentrations of dorzolamide demonstrated substantial lowering of intraocular pressure throughout the day when given twice daily (9% to 21%) or three times daily (14% to 24%). Although a dose-dependent response was observed immediately following the first dose, there were no significant differences between concentrations or dose response at either the twice or three times daily dosing regimen. Three times daily administration of 2% dorzolamide demonstrated a mean percent decrease in intraocular pressure of 18% to 22% throughout the day (mean decrease, 4.5 to 6.1 mm Hg). Dorzolamide appears to have substantial potential in the treatment of glaucoma and ocular hypertension.

Administration, Topical↗
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↗
PubMed1992

In vitro ingrowth of choroidal cells on Bruch's membrane.

Full thickness eyewall explants were made from human eyes, the retina and retinal pigment epithelium were removed, and the explants were maintained in vitro in Ham's F-10 medium with 20% foetal bovine serum. Cultured explants were examined by scanning and transmission electronmicroscopy after varying lengths of time. When in vitro, choroidal cells migrated across the cut edge of the explant onto the denuded Bruch's membrane where they subsequently showed production of extracellular matrix. In the human eye, ingrowth of choroidal cells on Bruch's membrane is found in macular degenerations, inflammatory chorioretinal disorders and subsequent to trauma. The in vitro model system presented in our study could facilitate evaluation of the dynamics underlying such ingrowth and also of factors affecting the course of this process.

Autoradiography↗
PubMed1992

Amino acid incorporation in cell cultures from eyes with pseudo-exfoliation material.

Conjunctival tissue was removed from eyes with and without pseudo-exfoliation material during cataract surgery. Cells derived from these samples were maintained in vitro. Confluent cultures were examined by transmission electron microscopy, and non-confluent as well as confluent cultures were examined for their ability to incorporate 3H-leucine and 3H-proline into TCA-precipitated material. Cells derived from both types of samples showed deposition of extracellular matrix, and a similar incorporation of the two amino acids. It is concluded that in vitro studies allow examination of basic metabolic patterns under varying conditions, and also a search for possible differences in such functions between tissues with and without production of pseudo-exfoliation material.

Anterior Eye Segment↗
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

Increased magnesium in aqueous humour from patients with senile cataract.

A previous observation of increased aqueous magnesium in eyes with senile cataract has been re-examined in a totally different material. The serum and aqueous level of calcium and magnesium from 34 patients with senile cataract were tested against comparable values from 4 patients with choroidal melanoma. In contrast to calcium, the magnesium aqueous/serum ratio was significantly higher in the cataract group. Possible explanations are suggested.

Adult↗
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

The middle-Norway eye-screening study. II. Prevalence of simple and capsular glaucoma.

In this population-based screening study, dealing with 1941 persons above 64 years of age from three different municipalities, the overall open-angle glaucoma prevalence was found to be 8.3%. The prevalence in the separate areas (7.0%, 8.6%, and 9.5%) were not statistically different. Roughly 30% of the population with pseudo-exfoliation syndrome had glaucoma, and 4.2% had ocular hypertension, whereas the corresponding figures for those without pseudo-exfoliation were 4% and 0.8%, respectively. The high glaucoma rates are partly due to the high pseudo-exfoliation prevalence in the area. The prevalence of the capsular glaucoma increased towards a maximum between 75 and 79 years of age, whereafter the curve declined. This may indicate reduced survival time of glaucomatous patients.

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↗