View clinical trials related to Ocular Physiology.
Filter by:This will be a multi-site, bilateral, dispensing, randomized, controlled, double-masked, 2×2 crossover study to evaluate ocular physiological response.
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.
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.
This is a bilateral-wear, dispensing, randomized, controlled, double-masked, 2-sequence × 2-period crossover study to evaluate ocular physiology following contact lens wear.
This is a bilateral wear, dispensing, randomized, controlled, double-masked, 2-sequence × 2-period crossover study to evaluate ocular physiology following approximately one week of contact lens wear.
This is a bilateral wear, dispensing, randomized, controlled, double-masked, 2-sequence ×2-period crossover study to evaluate ocular physiology following contact lens wear.
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.
Adequate perfusion and oxygenation is essential for the function of the inner retina. Although this is a well known fact, measurement of oxygen saturation in the eye is still a delicate and not fully explored task. However, recently a new instrument for the non-invasive measurement of retinal vessel oxygen saturation has been introduced. Unfortunately, no data about reproducibility in humans is yet available for this instrument. Consequently, the current study seeks to evaluate the short term and day to day reproducibility of retinal vessel oxygenation in healthy volunteers. 20 healthy volunteers will be included and oxygen saturation of retinal vessels will be determined. The reproducibility of the results will be tested by repeated measurements and the collected data will be independently analyzed by two observers.
Blood flow autoregulation is defined as the ability of a tissue to maintain a relatively constant flow, despite moderate alterations in perfusion pressure. Similar to the cerebral, renal, coronary and skeletal muscle circulations, the ocular vascular bed shows the property of flow autoregulation. This homeostatic mechanism allows blood supply to the eye to match metabolic demand during daily activities, such as changes in posture, or in more critical conditions. Autoregulation has been found to be a complex phenomenon, showing heterogeneity in its site and time course of action. Since metabolic, myogenic, neurogenic and possibly endothelium-related mechanisms may be involved, several factors may vary depending on the challenging stimulus, the vessel tone, or the degree of impairment of autoregulation. To study the dynamics of ocular autoregulation, it is necessary to introduce a step disturbance (stimulus) in ocular perfusion pressure and to record the responses of ocular blood flow continuously before and after this step disturbance. The investigators have employed a mechanical noninvasive technique to induce an ocular perfusion pressure step disturbance without drugs or changes in the concentration of vasoactive substances in the blood by using the thigh cuff technique inducing a small step decrease in ocular perfusion pressure. With this technique the investigators could show significant differences in the time response of blood velocities in the ophthalmic and middle cerebral artery. This clearly indicates different mechanisms to be responsible for autoregulatory mechanisms distal to the vessels. Interestingly our results indicate that in the ophthalmic artery a late vasoconstriction occurs. Many previous investigations have demonstrated that sympathetic nerve stimulation causes vasoconstriction in the ocular circulation. Accordingly, the present study tests the hypothesis that α2-adrenoceptors are involved in the dynamic regulation of blood flow in the ophthalmic and middle cerebral artery after a step decrease in perfusion pressure.
High arterial blood oxygen tension leads to vasoconstriction of retinal vessels, possibly related to an interaction between reactive oxygen species and endothelium-derived vasoactive factors. Vitamin C is a potent antioxidant capable of reversing endothelial dysfunction due to increased oxidant stress. Vitamin C appears to have vasodilatory properties, but the underlying mechanisms are not well understood. In the present study we hypothesized that hyperoxic vasoconstriction of retinal vessels could be diminished by vitamin C. Ocular blood flow will be determined by non-invasive methods, including laser Doppler velocimetry and the Zeiss retinal vessel analyser.