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Biomedical subjects

E Stefansson

Publications and source records attributed to E Stefansson.

28 records · Page 2Linked to original sources
PubMed1983

Effect of epinephrine on PO2 in anterior chamber.

A polarographic oxygen electrode was inserted through the cornea into the middle of the anterior chamber, and the aqueous humor PO2 was continuously monitored. Epinephrine hydrochloride applied topically to the cornea (1% Epifrin: 0.05 to 0.1 mL) or injected into the anterior chamber (Adrenalin Chloride: 1 mg/mL, 0.05 mL) caused a marked decrease in the anterior chamber PO2. This drop in anterior chamber PO2 was not simply due to mydriasis, since atropine sulfate administered in a similar fashion did not cause a notable drop in anterior chamber PO2, and epinephrine applied to eyes with the pupils previously dilated with atropine still caused the typical drop in anterior chamber PO2. The hypoxic effects of epinephrine were reversed by injection of an alpha-adrenergic blocker, phentolamine mesylate (5 mg/mL, 0.05 mL), into the anterior chamber.

Animals↗
PubMed1983

Oxygenation and vasodilatation in relation to diabetic and other proliferative retinopathies.

The features of proliferative retinopathies are reviewed with reference to the vasodilatation that is a common stage in their pathogenesis. Vasodilatation in the retina is discussed in terms of a model in which vessel wall stretch in the retinal venules leads to leakage and proliferation. The beneficial effects of treatments such as panretinal photocoagulation and vitrectomy on the retinal hemodynamics are shown to agree with the hypothetical model.

Animals↗
PubMed1983

The corneal contact lens and aqueous humor hypoxia in cats.

The cornea normally receives its oxygen from both the atmosphere and the aqueous humor. When a thick polymethylmethacrylate contact lens is placed on the cat cornea, access of atmospheric oxygen to the cornea is restricted, and the outer part of the cornea becomes hypoxic. This results in an increase in the oxygen flux from the aqueous humor into the cornea, and the oxygen tension in the aqueous humor decreases, as is demonstrated in this study. This increased oxygen flux from the aqueous into the cornea tends to alleviate the hypoxia caused by a corneal contact lens. Thus, the cornea can tolerate a thicker contact lens with less hypoxia than would be expected if only the oxygen supply from the atmosphere were considered.

Animals↗
PubMed1982

Argon laser intraocular photocoagulation.

Argon laser intraocular photocoagulation is now available during vitreous surgery, to treat retinal breaks and to give panretinal photocoagulation. Twenty patients, including phakic patients with gas-filled eyes, were treated using a new operative contact lens without complication. This intraoperative technique allows controlled rapid application of laser lesions at a safe distance from the retina, and eliminated the need for attempting treatment through the often hazy media of an irritated postoperative eye. A group of five rhesus monkeys were treated with various power settings to assess the histopathologic features of these laser lesions.

Animals↗
PubMed1982

Vitrectomy, lensectomy, and ocular oxygenation.

The effect of vitrectomy and lensectomy upon the anterior chamber oxygen tension of the cat eye was measured polarographically. After vitrectomy and lensectomy alone, a reduction of 12 mm Hg (35%) was observed and when retinal veins were also partially occluded, a reduction of 17 mm Hg (50%) was measured as compared with the normal oxygen tension (PO2) of 34 mm Hg. If vitrectomy and lensectomy allow aqueous to deliver oxygen from the anterior part of the eye to the retina, the poorer oxygenation of the iris and the improved oxygenation of the retina might explain both the development of rubeosis iridis and stabilization of proliferative diabetic retinopathy so commonly seen following vitrectomy.

Animals↗
PubMed1982

Panretinal photocoagulation and retinal oxygenation.

Panretinal photocoagulation destroys some of the photoreceptors and thereby reduces the oxygen consumption in the outer retina and allows more O2 to flow from the choroid to the inner retina. Measurements of the preretinal oxygen tension were made in rhesus monkeys that had portions of their retinas photocoagulated. With the animal breathing one atmosphere O2, the oxygen tension over photocoagulated areas of retina was significantly higher than the PO2 over normal, untreated areas of retina. It is proposed that the therapeutic effect of panretinal photocoagulation in diabetic retinopathy lies in the oxygenation of the inner retina from the choroid.

Animals↗
PubMed1981

Vasodilation and the etiology of diabetic retinopathy: a new model.

The evidence in support of the theory that retinal vascular stretching leads to leakage, formation of microaneurysms, and neovascularization is reviewed. The efficacy of photocoagulation and vitrectomy in controlling retinal microangiopathy accompanying diabetes is shown to depend upon reduction of the vascular dilatation. It is possible that the vascular dilatation in diabetes results from high blood glucose levels increasing oxygen consumption in the inner retina, with a resulting vascular dilatation to supply increased oxygen to the retina. This retinal vascular dilatation is the initial cause of the vascular pathology in diabetes.

Blood Glucose↗
PubMed1981

Increased retinal oxygen supply following pan-retinal photocoagulation and vitrectomy and lensectomy.

Panretinal photocoagulation as well as vitrectomy are the main treatment modalities for diabetic and other proliferative retinopathies. We show that both treatments introduce a new source of oxygen to the inner retina and propose that their efficacy in controlling the retinopathy results from their effect on the oxygenation of the inner retina. Panretinal photocoagulation reduces the oxygen consumption of the outer retina and allows more oxygen to diffuse to the inner retina from the choroid. Vitrectomy/lensectomy on the other hand allows aqueous humor to flow back to the retina and give oxygen to the inner retina which normally has a lower PO2 than aqueous humor. This causes the PO2 in aqueous humor to fall.

Animals↗
PubMedDate not supplied

Coronary blood flow in chronic insulin-dependent diabetic dogs.

Diabetic patients appear to be at an increased risk for perioperative morbidity and mortality following coronary artery bypass grafting. Many have suggested that microangiopathy is a primary cause. Using radionuclide labelled microspheres, we measured the perfusion of the subendocardium, midmyocardium, subepicardium, and the subendocardium/subepicardium ratio in alloxan-induced diabetic and normal dogs. We found no statistical difference in the myocardial perfusion of dogs made diabetic for five months when compared to normal dogs. By using repeated measures two-factor analysis of variance-regression model, changing blood glucose levels had no effect on coronary blood flow in either the diabetic or normal dogs.

Analysis of Variance↗