Investigative ophthalmology & visual science
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Invest. Ophthalmol. Vis. Sci. · Apr 2004
Fate of MHC-matched corneal allografts in Th1-deficient hosts.
To determine whether the Th1 cytokine, interferon (IFN)-gamma, is necessary for corneal graft rejection. ⋯ IFN-gamma is not necessary for the rejection of MHC-mismatched corneal grafts. However, IFN-gamma and Th1 immune mechanisms are necessary for the rejection of MHC-matched corneal allografts that confront the host with foreign minor histocompatibility antigens. The immune response in atopic patients, as in IFN-gamma KO mice, is characterized by cross-regulation of Th1 cytokines, such as IFN-gamma. The present results indicate that MHC matching dramatically reduces the risk of corneal graft rejection when IFN-gamma is depressed or absent. Thus, MHC matching may reduce the risk of corneal graft rejection in patients with atopic keratoconus.
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Invest. Ophthalmol. Vis. Sci. · Feb 2004
Excitability changes induced in the human primary visual cortex by transcranial direct current stimulation: direct electrophysiological evidence.
Transcranial direct current stimulation (tDCS) has been shown to modify the perception threshold of phosphenes elicited by transcranial magnetic stimulation (TMS). The current study was undertaken to examine whether tDCS, when applied over the occipital cortex, is also able to affect visual-evoked potentials (VEPs), which characterize occipital activation in response to visual stimulation, in a polarity-specific way. ⋯ tDCS appears to be a suitable method of inducing reversible excitability changes in a polarity-specific way, not only in the motor but also in the primary visual cortex. The duration of the induced aftereffects depends not only on stimulation duration but also on stimulation polarity. Cathodal stimulation seems to be more effective, in line with previous reports on the motor cortex.
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Invest. Ophthalmol. Vis. Sci. · Dec 2003
Five-year incidence of bilateral cause-specific visual impairment in the Melbourne Visual Impairment Project.
To describe the age-, gender-, and cause-specific 5-year incidence of bilateral visual impairment in participants in the Melbourne Visual Impairment Project, Victoria, Australia. ⋯ Undercorrected refractive error was the primary cause of new cases of visual impairment in this population. Further research is needed to understand the origin of this and to develop appropriate prevention measures. Age-related macular degeneration is the primary cause of severe or profound vision loss in Australia. This disease requires further investigation for effective cure and preventive strategies.
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Invest. Ophthalmol. Vis. Sci. · Dec 2003
Methods and perceptual thresholds for short-term electrical stimulation of human retina with microelectrode arrays.
To report methods for performing epiretinal electrical stimulation with microfabricated electrode arrays and determining perceptual thresholds on awake human volunteers during acute surgical trials. ⋯ Threshold charge densities in severely blind patients were substantially higher than that in a normal-sighted patient. Charge densities in blind patients always exceeded one seemingly reasonable estimate of safe stimulation. The potential adversity of long-term stimulation of the retina by a prosthesis has yet to be determined.
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Invest. Ophthalmol. Vis. Sci. · Nov 2003
Randomized Controlled Trial Clinical TrialEffects of sildenafil on retinal blood flow and flicker-induced retinal vasodilatation in healthy subjects.
Sildenafil is a specific inhibitor of phosphodiesterase V, which is widely used for the treatment of erectile dysfunction. Sildenafil has been shown to induce vasodilation in several vascular beds by inhibiting the cGMP breakdown. The present study was conducted to investigate whether sildenafil increases blood flow in the human retina. ⋯ The data indicate that sildenafil increases retinal venous diameters and retinal blood flow in healthy subjects. By contrast, it does not affect intraocular pressure and flicker-induced retinal vasodilation. Further studies are needed to elucidate whether this drug may be therapeutically used in retinal ischemic disease.