Biomedical subjects

E Stefansson

Publications and source records attributed to E Stefansson.

At least 19 recordsLinked to original sources

PubMed2005

The time pattern of bilateral exudative age-related macular degeneration.

PURPOSE: To study time patterns in bilateral exudative age-related macular degeneration (AMD) and the pattern of drusen before and after the onset of exudative AMD. MATERIAL AND METHODS: Out of 2220 individuals in the Icelandic genetic study of AMD, 151 had bilateral exudative AMD. We searched for previous records in the Icelandic University Retina Unit. For the 65 patients with a fluorescein angiography record of both eyes, we established the time between the onset of disease in each eye. For the 53 patients with colour fundus photographs of the latter eye taken prior to the occurrence of exudative disease, we graded the drusen before and after the onset of exudative AMD in the second eye. RESULTS: The time interval between the onset of exudative AMD in the first and second eyes was 2.5 years (95% CI: 1.8-3.2; n = 65) and the median was 1.8 years. In 82% of cases the second eye was affected within 4 years. Soft drusen in the macula were found in 95% of eyes that later developed exudative disease (n = 53). Soft and hard drusen decreased in number in the central macula following the development of exudative disease. CONCLUSIONS: Bilateral exudative AMD develops within a few years in both eyes. Drusen are less visible following the onset of exudative AMD in the second eye.

Aged↗

PubMed2001

Intranasal administration of midazolam in a cyclodextrin based formulation: bioavailability and clinical evaluation in humans.

Intranasal administration of midazolam has been of particular interest because of the rapid and reliable onset of action, predictable effects, and avoidance of injections. The available intravenous formulation (Dormicum i.v. solution from Hoffmann-La Roche) is however less than optimal for intranasal administration due to low midazolam concentration and acidity of the formulation (pH 3.0-3.3). In this study midazolam was formulated in aqueous sulfobutylether-beta-cyclodextrin buffer solution. The nasal spray was tested in 12 healthy volunteers and compared to intravenous midazolam in an open crossover trial. Clinical sedation effects, irritation, and serum drug levels were monitored. The absolute bioavailability of midazolam in the nasal formulation was determined to be 64 +/- 19% (mean +/- standard deviation). The peak serum concentration from nasal application, 42 +/- 11 ng ml-1, was reached within 10-15 min following administration and clinical sedative effects were observed within 5 to 10 min and lasted for about 40 min. Intravenous administration gave clinical sedative effects within 3 to 4 min, which lasted for about 35 minutes. Mild to moderate, transient irritation of nasal and pharyngeal mucosa was reported. The nasal formulation approaches the intravenous form in speed of absorption, serum concentration and clinical sedation effect. No serious side effects were observed.

Administration, Intranasal↗

PubMed1999

Chronic open-angle glaucoma and associated ophthalmic findings in monozygotic twins and their spouses in Iceland.

PURPOSE: To determine the concordance of glaucoma and ocular parameters in monozygotic twins and their spouses. METHODS: This was a prospective study that included 50 twin pairs 55 years of age or older and 47 of their spouses. Zygosity was determined by genetic laboratory testing. RESULTS: The concordance of open-angle glaucoma in monozygotic twin pairs was 98.0%, which significantly exceeded that of twin/spouse pairs (70.2%). There was a significant association in mean intraocular pressure (IOP), mean axial length, anterior chamber depth, and refractive error in the twin pairs. However, there was no association between the twins and their spouses for these ocular parameters. Eight twin pairs were found to have pseudoexfoliation syndrome (PXFS), five of which were concordant. There was no association between glaucoma and mean axial length or glaucoma and refractive error in the twin pairs studied. CONCLUSION: The statistically significant higher concordance of glaucoma--and the high correlation of mean IOP, mean axial length, anterior chamber depth, and refractive error--in twin pairs and the lack of association of these factors in twin/spouse pairs strongly suggests the importance of genetic factors for these ocular parameters.

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PubMed1998

Is pseudoexfoliation syndrome inherited? A review of genetic and nongenetic factors and a new observation.

Pseudoexfoliation (PEX) syndrome is the commonest identifiable cause of open-angle glaucoma worldwide. PEX is characterized clinically by small whitish deposits of fibrillar-granular material in the anterior segment of the eye. Despite its prevalence and potential for ophthalmic morbidity, surprisingly little is known about the etiology and pathogenesis of PEX. This article reviews the literature and presents evidence regarding genetic and nongenetic arguments for the etiology of pseudoexfoliation. Lines of evidence that support a genetic basis for PEX include transmission in two-generation families, twin studies, an increased risk of PEX in relatives of affected patients, and HLA studies. Nearly all pedigrees in the literature, and our own experience with PEX families in Iceland and Canada, suggest maternal transmission, raising the possibilities of mitochondrial inheritance, X-linked inheritance, and autosomal inheritance with genomic imprinting. A number of nongenetic factors have also been evaluated for their possible implication in the development of PEX. These include ultraviolet light, autoimmunity, slow virus infection, and trauma. It is possible that a combination of genetic and nongenetic factors may be involved in the etiology and pathogenesis of PEX, i.e. it may be a multifactorial disorder. Further studies with larger numbers of patients are needed to delineate more clearly the contribution of genetic (nuclear DNA, mitochondrial DNA or both) and nongenetic factors to the development of pseudoexfoliation syndrome and pseudoexfoliation glaucoma.

Autoimmunity↗

PubMed1990

Oxygen and diabetic eye disease.

In 1956, Wise suggested that retinal hypoxia stimulated retinal neovascularization in the ischemic proliferative retinopathies. Although not directly proven, this theory is strongly supported by a wealth of circumstantial information. Two treatment modalities, vitrectomy and panretinal photocoagulation, have been shown to be effective against retinal neovascularization in diabetics. Both of these treatment modalities improve retinal oxygenation, and we propose that this is the mechanism through which they halt retinal neovascularization. The mechanism for improving retinal oxygenation is different for the two treatment modalities. In the case of panretinal photocoagulation, the new oxygen supply comes from the choroid through the laser scar in the outer retina. In the case of vitrectomy, it comes from the vitreous cavity itself, but the end result is the same. We have expanded Wise's hypothesis to include these two treatment modalities, which were not known at the time of Wise's original paper.

Animals↗

PubMed1990

Retinal ischemia and cell proliferation in the rat: the role of soluble mitogens.

Temporary retinal ischemia in the rat leads to a proliferation of endothelial cells and glial cells. We tested the hypothesis that this proliferation is caused by a release of soluble mitogens from the ischemic retina. Conditioned media were prepared from normal rat retina and from retina that had undergone 2 h ischemia and 48 h reperfusion, at which time it showed intense mitotic activity. The conditioned media were placed in cultures of fibroblasts, bovine adrenal capillary endothelial cells, and rat brain astrocytes. Cell proliferation in vitro was stimulated by the retinal extracts in all cell cultures. However, the cell proliferation in cultures with conditioned media from normal retina was similar to that in cultures with conditioned media from ischemic and proliferating retina. Although these data are consistent with the presence of soluble growth factors in the retina, they also indicate that release of these growth factors into the surrounding milieu after transient retinal ischemia is not altered to a degree that would explain the dramatic increase in mitosis.

Animals↗

PubMed1990

Retinal oxygen consumption in vitro. The effect of diabetes mellitus, oxygen and glucose.

In diabetes mellitus, the retina is exposed to fluctuations in blood glucose concentrations, presumed decreases in oxygen availability and other metabolic disturbances induced by the disease. These metabolic phenomena may play a role in diabetic retinopathy. To understand these processes better, we measured oxygen consumption in vitro in retinas from normal and diabetic rabbits and examined the effect of oxygen and glucose concentration on retinal respiration. Retinal oxygen consumption is decreased in diabetic retinas compared to normal rabbit retinas (0.56 +/- 0.09 ml of oxygen per min per mg dry weight in normal and 0.40 +/- 0.07 ml of oxygen per min per mg dry weight in diabetic retinas). Retinal oxygen consumption is elevated if the oxygen tension is raised above normal in both groups. Glucose concentration did not significantly effect the oxygen consumption of the retina in either group.

Animals↗

PubMed1990

Endocapsular hypopyon: a clinical sign of localized endophthalmitis.

Chronic intraocular infection following cataract extraction and intraocular lens (IOL) implantation has been documented by several authors. We report a case of chronic, bacterial endophthalmitis that clinically correlates with previous pathologic studies in which the focus of infection was sequestered in the capsular sac between the IOL and the posterior lens capsule. Successful management did not require IOL removal.

Aged↗

PubMed1990

Basic fibroblast growth factor stimulates 3H-thymidine uptake in retinal venular and capillary endothelial cells in vivo.

Recent studies have found basic fibroblast growth factor (bFGF), an angiogenic peptide, in retina and have suggested that bFGF is responsible for retinal vascular proliferation. To test the hypothesis that bFGF stimulates 3H-thymidine uptake in retinal vascular cells in vivo, we injected bFGF (100 ng) into the vitreous cavity of six cats at 0 hr and again at 24 hr. Eight control eyes received boiled bFGF or no injection. After 46 hr, 3H-thymidine was injected into the vitreous cavity of all eyes and 2 hr later the eyes were enucleated. Intense 3H-thymidine uptake was seen in eyes with bFGF (56 +/- 20 SD positive cells per section) but not in control eyes (7-10 positive cells per section (P less than 0.001). Trypsin digest preparations showed that the thymidine uptake was predominantly in the venular (89%) and capillary (10%) endothelium and not in arterioles (1%) (P less than 0.001). The data suggest that retinal venular endothelial cells respond preferentially to exogenous bFGF, and in part may explain their prominent role in the neovascular process. In a second group of experiments to test the hypothesis that retinal ischemia releases a diffusable factor similar to bFGF that can cause 3H-thymidine uptake in retinal vascular cells, we created branch retinal vein occlusion in six cat eyes. The fellow eyes received no injections. In the eyes with branch vein occlusion there was an intense 3H-thymidine uptake within the distribution of the occluded vein (84 +/- 77 SD positive cells per section), but none in the areas outside the occluded vein (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Results of silicone oil removal in advanced proliferative vitreoretinopathy.

We reviewed the results of silicone oil removal after vitreous surgery for recurrent retinal detachment with proliferative vitreoretinopathy in 55 eyes. The minimum follow-up period was six months. Retinal detachment recurred in five eyes (9%). Evidence of recurrent epiretinal membrane formation at the time of or after silicone oil removal was noted in 21 eyes (38%). Penetrating keratoplasty combined with silicone oil removal was successful in five of six patients. Mild corneal changes noted in ten eyes (18%) remained the same or cleared in seven eyes after silicone oil removal. Overall, postoperative visual acuity improved in 24 eyes (44%), remained the same in 18 eyes (33%), and decreased in 13 (24%). In 22 eyes without clinical evidence of silicone-associated complications at the time of silicone oil removal, postoperative visual acuity remained unchanged or improved in 20 (91%).

Cornea↗

PubMed1989

Intraocular oxygen tension measured with a fiber-optic sensor in normal and diabetic dogs.

A new fiber-optic O2 sensor was used to measure the O2 tension in the living dog eye, and the results were compared with simultaneous O2 tension measurements with polarographic electrodes. The fiber-optic sensor and the polarographic electrodes gave similar readings of anterior chamber O2 tension and gave an identical response to elevation of inspired O2 levels. In the preretinal vitreous, the fiber-optic probe measured the O2 tension 26 +/- 5 mmHg (means +/- SD, n = 5), whereas the polarographic electrode showed 23 +/- 7 mmHg (means +/- SD, n = 5) in the contralateral eyes. Breathing 100% O2 raised the preretinal O2 tension similarly with both systems. Preretinal O2 tension was measured with the fiber-optic sensor in seven alloxan diabetic dogs and was 26 +/- 7 mmHg, which is not significantly different from normal dogs. The fiber-optic sensor has some advantages over the polarographic electrodes. The fiber-optic sensor does not consume O2 and is not dependent on the diffusion characteristics of the medium or changes due to stirring or fluid currents.

Animals↗

PubMed1989

Sickness absenteeism in an engineering industry--an analysis with special reference to absence for neck and upper extremity symptoms.

Neck and upper extremity symptoms (NES) are reported to increase among industrial workers. In order to quantify sickness absenteeism and relate it to some factors a questionnaire study was performed among 2,814 workers occupied at a Swedish engineering industry. Questions pertaining to age, sex, worker category, work with vibrating handtools, type of job and smoking habits were analyzed and correlated to sickness absenteeism for the previous year (1983). We found that the average days lost for personal illness was 17.2 days; 16.2 for men and 23.5 days for women. Ninety-four persons, 77 men and 17 women comprising 3.0% of all employees were sicklisted for NES corresponding to 3.3% of total sickness time lost. Blue-collar workers were sicklisted for NES five times more often than white collar workers and women in type 3 jobs (high NE stress), twice that of men occupied in the same type of job. Smokers had significantly higher absenteeism than non-smokers for any reason studied including NES. The study indicated a high prevalence of present NES problems (23%) but also that NES as a cause of leave of absence was relatively rare (3%).

Absenteeism↗

PubMed1989

The correlation between work environment and the occurrence of cervicobrachial symptoms.

The correlation between symptoms from the neck and upper extremities and some individual and work-related factors was analyzed in 2814 industrial workers. Physical stress by type of job was the factor most strongly correlated with ongoing cervicobrachial symptoms. Symptoms from the neck and upper extremities were twice as common in workers who used vibrating hand tools. Mental stress at the onset of the symptoms was associated with an increased prevalence of trapezius myalgia and with lateral humeral epicondylitis and "radial tunnel syndrome" in the dominant arm. Women had about double the rate of cervicobrachial symptoms as did men. Short stature increased the rate of symptoms from the neck, shoulders, and hands as did overweight. Playing of racquet sports decreased the risk of symptoms from the neck and hands.

Analysis of Variance↗

PubMed1989

Local hypothermia protects the retina from ischemia. A quantitative study in the rat.

We developed a quantitative histologic method for assessing injury in the rat retina due to transient ischemia. We used this technique to test the effectiveness of local hypothermia and allopurinol, an inhibitor of oxygen-free radical formation, in reducing ischemia/reperfusion injury in the rat retina. Retinal ischemia and reperfusion was produced by transient ligation of the optic nerve. Histologic evaluation by a masked observer was based on the average count of nonpyknotic nuclei in the inner nuclear layer of the retina from eight high power fields (X100) in one 5 microns thick sagital section at or near the optic nerve. A sharp increase in tissue damage occurs between 90 and 120 min of ischemia. Ischemia for periods of 60 and 90 min produced mild damage while periods of 120 and 240 min produced severe damage. Hypothermia protected the retina significantly from 120 min of ischemic injury (P less than 0.001 student t-test, compared to 120 min control), while allopurinol had no protective effect.

Allopurinol↗

PubMed1987

The effect of timolol on anterior-chamber oxygenation.

The effect of timolol maleate, a nonspecific beta-blocking agent, on anterior-segment oxygenation was studied using oxygen-sensitive microelectrodes inserted into the mid-anterior chamber of 13 cat eyes. The anterior-chamber oxygen tension was monitored continuously for two hours following the topical application of three drops of timolol 0.5%. Although a small, but significant, decline in oxygen tension of 19% was observed over the initial 90 minutes (P less than or equal to .05), the overall 10% decrease at the end of two hours was not considered either clinically or statistically significant when compared with a group of controls. Timolol, since it does not contribute significantly to hypoxia, may therefore be a more prudent choice for lowering intraocular pressure in disorders where hypoxia is believed to play an important role, such as in neovascular glaucoma and sickle-cell hyphema.

Animals↗

PubMed1987

Retinal oxygenation from the choroid in hyperoxia.

The extraordinarily high rate of blood flow in the cat choroid allows the choroidal oxygen tension to rise to levels close to the arterial PO2, even with oxygen enriched breathing mixtures. The high PO2 in the choroid can elevate the oxygen tension of the inner retina above the saturation PO2 of hemoglobin when oxygen enriched breathing mixtures at one atmosphere or less are used as shown by polarographic oxygen tension measurements in the preretinal vitreous in cats.

Animals↗

PubMed1986

The relationship between retinal vessel tortuosity, diameter, and transmural pressure.

Increases in retinal vein tortuosity are thought to be caused by increases in vascular transmural pressure. We have attempted to determine the relationship between retinal vessel tortuosity, diameter, and transmural pressure by examining the effects of changes in transmural pressure on latex tubes with fixed ends. As the transmural pressure is raised, tube diameter increases, but tortuosity does not begin increasing until a critical pressure is reached. Above the critical pressure, tortuosity increases more rapidly than diameter. Our results support the above hypothesis and also suggest that at high transmural pressures, retinal vessel tortuosity is a more sensitive indicator than is the diameter of changes in retinal venous transmural pressure, but diameter is more sensitive than tortuosity at lower pressures.

Humans↗

PubMed1984

Neovascularization of the iris: an experimental model in cats.

Neovascularization of the iris was induced in cats by removing the vitreous and lens and creating a rhegmatogenous retinal detachment. The presence of new blood vessels on the anterior surface of the iris was verified from the second month onward by slit lamp examination, as well as by light microscopy six to twelve months after the operation. Control eyes undergoing vitrectomy and lensectomy, but without retinal detachment, did not develop rubeosis iridis. This model may allow investigation into causes and therapy of rubeosis iridis.

Animals↗