Oguchi's disease: two cases and literature review

Oguchi's disease is a rare form of congenital stationary night blindness, associated with light-dependent golden fundus discoloration. In this report, we describe two cases of Oguchi's disease, both of which had two characteristic features: congenital stationary night blindness and fundoscopic manifestation of the Mizuo–Nakamura phenomenon. In both patients, fundus examination revealed a metallic sheen throughout the retina, which disappeared after 2.5 hours of dark adaptation, suggestive of the Mizuo–Nakamura phenomenon. The characteristic electroretinogram (ERG) changes (i.e., un-recordable rod response and reductions of maximal response, oscillatory potentials, and flicker response) in these patients confirmed the clinical diagnosis of Oguchi's disease. Furthermore, we discuss the results of our literature search for evidence concerning the diagnosis and pathogenesis of this rare disease. Further studies regarding the genes involved in phototransduction and light adaptation are needed to determine the pathogenesis of this rare disease.

No evidence for entrainment: endogenous gamma oscillations and rhythmic flicker responses coexist in visual cortex

Motivated by the plethora of studies associating gamma oscillations (∼30-100 Hz) with various neuronal processes, including inter-regional communication and neuroprotection, we asked if endogenous gamma oscillations in the human brain can be entrained by rhythmic photic stimulation. The photic drive produced a robust Magnetoencephalography (MEG) response in visual cortex up to frequencies of about 80 Hz. Strong, endogenous gamma oscillations were induced using moving grating stimuli as repeatedly shown in previous research. When superimposing the flicker and the gratings, there was no evidence for phase or frequency entrainment of the endogenous gamma oscillations by the photic drive. Rather – as supported by source modelling – our results show that the flicker response and the endogenous gamma oscillations coexist and are generated by different neuronal populations in visual cortex. Our findings challenge the notion that neuronal entrainment by visual stimulation generalises to cortical gamma oscillations.

Effect of Increased Oxygen Tension on Flicker-Induced Vasodilatation in the Human Retina

In the retina, blood flow and neural activity are tightly coupled. Stimulation of the retina with flickering light is accompanied by an increase in blood flow. The current study seeks to investigate whether an increase in oxygen tension modulates flicker (FL)-induced vasodilatation in the human retina. A total of 52 healthy volunteers were included. Via a breathing mask, 100% oxygen (O2) was administered in one, a mixture of 8% carbon dioxide and 92% oxygen (C/O) in a second cohort. Retinal vessel diameters were measured with a Vessel Analyzer and FL responses were assessed before and during the breathing periods. At baseline, FL stimulation increased retinal vessel diameters by +3.7 ± 2.3% in arteries and by +5.1 ± 3.7% in veins. Breathing of C/O led to a decrease in arterial (−9.0 ±,6.9%) and venous (−11.3 ± 5.9%) vessel calibers. Flicker response was increased to 5.7 ± 2.5% in arteries and to 8.6 ± 4.1% in veins. Breathing of pure O2 induced a vasoconstriction of vessel diameters by −14.0 ± 5.3% in arteries and −18.4 ± 7.0% in veins and increased FL responses in arteries (+6.2 ± 2.8%) and veins (+7.2 ± 3.1%). Systemic hyperoxia increases FL-induced retinal vasodilatation in the retina. The mechanism by which oxygen modulates the hyperemic response to FL stimulation remains to be elucidated.