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Showing 1-10 of 10 trials
NCT06161012
This will be a multi-site, bilateral, dispensing, randomized, controlled, double-masked, 2×2 crossover study to evaluate ocular physiological response.
NCT05713552
This will be a single-visit, randomized, double-masked, bilateral wear, non-dispensing, 2-sequence × 2-period crossover study to evaluate subject reported ocular symptoms.
NCT05530889
This will be a prospective, randomized, bilateral eye, crossover, non-masked single site pilot study to compare the severity of symptoms of itching between test and control lens after two weeks of wear.
NCT00406731
Autoregulation is the ability of a vascular bed to maintain blood flow despite changes in perfusion pressure. The existence of an effective autoregulation in the optic nerve circulation has been shown in animals and humans. The exact mechanism behind this autoregulation is still unknown. The motive for the investigation of optic nerve head (ONH) blood flow autoregulation is to enhance the understanding of pathologic eye conditions associated with ocular vascular disorders. To clarify the regulatory mechanisms of ONH microcirculation is of critical importance to understand the pathophysiology of glaucoma because there is evidence that glaucoma is associated with optic nerve head ischemia. Several studies indicate that a disturbed autoregulation might contribute to glaucomatous optic neuropathy. Previous findings suggest endothelial dysfunction in glaucomatous optic neuropathy, in particular alterations in endothelin- and nitric oxide- system, which both play an important role in local regulation of vascular tone. In the present study, changes in ocular perfusion pressure will be performed during administration of drugs, which may potentially alter the pressure-flow relationship. These drugs include endothelin-1 and the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA).
NCT00712400
Latanoprost is a synthetic prodrug of 17-phenyl-substituted prostaglandin F2α analog. Used at a dose of one drop per day, it has been reported to produce a 30 to 35% reduction in intraocular pressure. Its mechanism of activation involves augmentation of the eye's natural uveoscleral outflow capacity . There is evidence that ocular blood flow plays a role in the clinical course of glaucoma. Glaucoma medication that lowers IOP simultaneously increases ocular blood perfusion pressure, which in turn may increase ocular blood flow. This could well contribute to the partially contradicting results concerning ocular hemodynamic effects of latanoprost. In vitro studies indicate that latanoprost has no effect on ocular vascular tone in therapeutical doses. By contrast, it has been reported in several studies that latanoprost 0.005% increases pulsatile ocular blood flow in patients with primary open angle glaucoma and normal tension glaucoma. This increase in pulsatile ocular blood flow mainly reflects an increase in the choroidal circulation. Little is known about the potential effect of latanoprost on choroidal blood flow regulation in humans. The present study therefore tries to elucidate whether treatment with latanoprost may alter choroidal blood flow regulation during artificial changes in ocular perfusion pressure. In addition, the present study aims to clarify whether the change in choroidal blood flow after latanoprost administration are due to direct vasoactive effects or due to the increase in ocular perfusion pressure. The second alternative may have important implications on our understanding of glaucoma treatment, because reduction of IOP may then per se result in normalization of ocular blood flow regulation.
NCT00708357
Nitric oxide (NO) is a potent endothelium-derived vasodilatator that plays a major role in the control of ocular blood flow. Endothelial NO synthase (eNOS) is one of three isoforms of NOS producing NO through hydroxylation of L-arginine. The eNOS gene is located on the long arm of chromosome 7, and different polymorphic variations have been identified. These single nucleotide polymorphisms (sNP´s) have the ability to change transcription activity and therefore enzyme levels. Recent data indicate that the T -786C polymorphism (especially the homozygous variant) is associated with reduced eNOS activity and consequently impaired NO production. In the present study the investigators want to investigate if the T -786C eNOS gene polymorphism determines choroidal and optic nerve head blood flow.
NCT01663688
The purpose of this clinical study is to collect and evaluate the data from eye scans using an investigational three-dimensional eye imaging photography device called the Nidek Optical Coherence Tomography (OCT) RS-3000. OCT stands for Optical Coherence Tomography, a technique that uses invisible wavelengths of light to make detailed images of the tissues at the back of the eye. These images provide information that physicians may use to help diagnose eye conditions and/or to monitor changes in the eye during treatment.
NCT00431730
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.
NCT00275730
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.
NCT00431548
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.