View clinical trials related to Ocular Physiology.
Filter by:A number of common eye diseases such as retinal artery and vein occlusion, diabetic retinopathy, age-related macular degeneration, glaucoma and anterior ischemic optic neuropathy are associated with ocular perfusion abnormalities. Although this is well recognized there is not much possibility to improve blood flow to the posterior pole of the eye in these diseases. Since many years, moxaverine is used in the therapy of perfusion abnormalities in the brain, the heart and the extremities. This is based on a direct vasodilator effect of the drug, but also on the rheological properties of red blood cells. Whether moxaverine affects blood flow in the eye is unknown. The present study aims to investigate whether moxaverine may improves blood flow in the eye after systemic administration.
Age related macular degeneration (AMD) is a multifactorial disease with a strong genetic component. Most importantly a genetic polymorphism in the gene encoding for the complement factor H (CFH) has been recently identified which is highly associated with an increased risk of developing AMD. This Tyr402His polymorphism located on chromosome 1q31 has been implicated to play a role in the development of the disease. Given that it is known that impaired regulation of choroidal vascular tone is present in patients with AMD, the current study seeks to investigate whether the Tyr402His polymorphism is associated with altered choroidal autoregulation in healthy subjects. For this purpose a total of 100 healthy volunteers will be included in order to test the hypothesis that an impaired regulation of choroidal blood flow is present in subjects with homozygous Tyr402His variant.
Glaucoma is one of the most common causes of blindness in the industrialized nations. For a long time glaucoma has been defined as a disease in which high intraocular pressure (IOP) leads to irreversible optic disc damage and subsequent visual field loss. However, recent investigations show that IOP is not the only factor that is involved in the glaucomatous process leading to retinal ganglion cell death. The role of vascular factors in the pathogenesis of glaucoma has recently received much attention based on animal experiments and epidemiological studies. The main focus of glaucoma is still directed towards a decrease in IOP. There is, however, also considerable interest whether antiglaucoma drugs influence ocular perfusion. Although measurement of ocular blood flow is still difficult, a number of innovative techniques have been realized which cover different aspects of ocular perfusion. In the present study Xalacom® (latanoprost/timolol) and the fixed combination of Combigan® (brimonidine/timolol) will be compared with respect to their IOP lowering efficacy as well as their ocular hemodynamic effects.
Habitual smoking is associated with an increased risk of coronary artery disease, cerebral and peripheral vascular disease, including ocular diseases like age-related macular degeneration or diabetic retinopathy. Data of a recent study performed in the investigators lab revealed abnormal choroidal blood flow regulation in chronic smokers as compared to age-matched non-smoking subjects during isometric exercise. However, no information is yet available about the regulation of retinal vascular tone in habitual smokers. Thus, in the current study, the investigators set out to investigate whether the regulation of retinal vessels diameters is affected in habitual smokers. It has been shown in several reports that stimulation with diffuse luminance flicker, increases retinal arterial and venous diameters, indicating for the ability of the retina to adapt to changing metabolic demands. In the current study we use this effect as a tool to investigate whether the flicker induced vasodilatation is affected in habitual smokers. This would indicate for an impaired vascular regulation process in smokers.
Ocular lesions, including cotton wool spots and retinal hemorrhage, are a common feature of HIV infection and acquired immunodeficiency syndrome (AIDS). The aetiology of these apparently vasoocclusive phenomena in HIV related retinopathy is not well understood. Several hypotheses including infectious damage of the retinal vasculature and altered retinal hemodynamics have been postulated. The latter would be compatible with the theory that the retina of HIV patients is hypoxic. However, direct measurement of oxygen tension in the retina is not possible and indirect methods have to be employed. The study objective was to investigate the reactivity in retinal blood flow to 100% oxygen breathing in patients with HIV.
There is evidence from a variety of animal studies that choroidal blood flow is under neural control. By contrast, only little information is available from human studies. Recent results indicate that a light/dark transition is associated with a short lasting reduction in choroidal blood flow. We have shown that during unilateral dark/light transition both eyes react with choroidal vasoconstriction strongly indicating a neural mechanism. The present studies investigate this possibility by using pharmacological interventions. The pharmacological agents tested include a nitric oxide synthase inhibitor, an alpha-receptor agonist (as a control substance for the blood pressure increasing nitric oxide synthase inhibitor), a muscarinic receptor blocker, and a non-specific beta-blocker. These drugs were chosen on the basis of previous animal experiments, as the systems, which are specifically influenced by these substances, are likely involved in neural control of choroidal blood flow.
Brimonidine tartrate is an alpha-2 agonist ocular hypotensive drug that exerts its effect by causing both a decrease in aqueous production and an increase in uveoscleral outflow. It has been proven to reduce increased intraocular pressure in glaucoma and ocular hypertension. As an alpha 2 agonist Brimonidine belongs to the same class of drugs as Clonidine; however, its molecular structure is sufficiently different to make it more selective for the alpha 2 receptor than Clonidine. Unlike Clonidine, Brimonidine does not appear to have an effect on the central nervous system and therefore does not cause sedation or systemic hypotension. In addition to their known effect of lowering intraocular pressure, alpha 2 adrenoceptor agonists are neuroprotective. It has, however, been shown that Brimonidine is a very potent vasoconstrictor in the ciliary body thus reducing aqueous humor production. Little is, however, known about potential vasoconstrictor effects of Brimonidine in the posterior pole of the eye. This is of clinical importance, because optic nerve head ischemia appears to contribute to glaucoma pathophysiology. This study is performed to investigate the effects of topical Clonidine vs. topical Brimonidine on choroidal blood flow and intraocular pressure during isometric exercise.
There is evidence from a variety of animal studies that choroidal blood flow is under neural control. By contrast, only little information is available from human studies. Recent results indicate that a light/dark transition is associated with a reduction in choroidal blood flow due to an unknown mechanism. We have shown that during unilateral dark/light transitions both eyes react with choroidal vasoconstriction strongly indicating a neural mechanism responsible for the blood flow changes. Dopamine has been discussed as a chemical messenger for light adaptation. However, dopaminergic effects in the eye are not restricted to synaptic sites of release, but dopamine also diffuses to the outer retinal layers and pigment epithelium. Accordingly, dopaminergic effects also include a modulatory role on retinal vessel diameter and animal studies provide evidence for vasodilatory effects in the choroid. There is evidence that during darkness retinal and choroidal dopamine levels decrease. Accordingly, dopamine could provide a modulatory input to the light/dark transition induced changes of choroidal circulation. The aim of the present study is to test this hypothesis.
Autoregulation is the ability of a vascular bed to maintain blood flow despite changes in perfusion pressure. For a long time it had been assumed that the choroid is a strictly passive vascular bed, which shows no autoregulation. However, recently several groups have identified some autoregulatory capacity of the human choroid. In the brain and the retina the mechanism behind autoregulation is most likely linked to changes in transmural pressure. In this model arterioles change their vascular tone depending on the pressure inside the vessel and outside the vessel. In the choroid, several observations argue against a direct involvement of arterioles. In a previous project we were able to identify that the nitric oxide (NO) - system as well as the endothelin system are involved in choroidal blood flow regulation during isometric exercise. In the present study autoregulation of the choroid during isometric exercise will be investigated and the pressure/flow relationships will be observed in the absence or presence of a calcium antagonist - nifedipine.
Prostaglandins (PG) are known to alter regional ocular blood flow and exhibit vasoactive properties in isolated ocular blood vessels. A variety of animal experiments indicate that endogenous PGs play a role in the regulation of retinal (RBF) and choroidal (ChBF) blood flow. There is also evidence that the prostaglandin pathway is involved in the activation of NO production in humans, however, the mechanisms for interactions between PG and NO in ocular vasculature are still unclear. Animal studies suggest that retinal and choroidal blood flow decrease after administration of indomethacin (a nonspecific cyclooxygenase inhibitor). More recently, it has been shown that indomethacin injected intravenously decreased optic nerve oxygen tension and reduced the CO2 reactivity. This is probably the result of decreased blood flow through vasoconstriction of vessels in the optic nerve. Systemic administration of indomethacin also diminishes cerebral, renal and mesenteric blood flow by an unknown mechanism. However, no clinical trials exist so far investigating the effects of indomethacin on ocular blood flow. Therefore, the aim of this study is to investigate the effect of indomethacin on ocular blood flow in healthy humans.