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Inflammatory Disorders of the Nervous System
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Reduced visual acuity, which varies from a slight dulling of color vision to complete monocular blindness, together with pain around or behind the eye that is exacerbated by eye movement or touching the eye, are symptoms of optic neuritis. Flashes of light on eye movement may occur (phosphenes). The signs include a central or paracentral scotoma in most patients, particularly using a red target (most of the optic nerve fibers transmit information from the macula), and a swollen optic disc (papillitis) in the acute phase if there is demyelination of the anterior part of the optic nerve. A unilateral afferent pupillary defect may be observed. Optic disc pallor due to optic atrophy ensues later.
Artificial vision and retinal prostheses
Published in A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha, Vitreoretinal Surgical Techniques, 2019
Humayun Mark S, Lakhanpal Rohit R, Weiland James D
that electrical stimulation of the visual cortex caused his subject to detect a spot of light (phosphene). He further demonstrated that the spatial psychophysical location of this phosphene depended upon the location of the electrical stimulation point over the cortex.17 The first serious effort (by today’s standards) to establish an electrical artificial vision system was undertaken some 40 years ago by Giles Brindley. Brindley’s implantation of an 80-electrode device onto the visual cortex of a blind patient revealed the possibilities of electrical stimulation to restore vision and the barriers to implementation of a suitable device. Brindley’s pioneering work has influenced all subsequent major efforts in the area of electronic visual prostheses. In the past 50 years, exponential advances in our understanding of electronics, physiology, and medicine have enabled the development of implantable microelectronic systems that overcome the shortcomings of Brindley’s large, immobile visual stimulator.16,18
Technologies for vision impairment
Published in John Ravenscroft, The Routledge Handbook of Visual Impairment, 2019
Lauren N. Ayton, Penelope J. Allen, Carla J. Abbott, Matthew A. Petoe
It is important to note that the visual sensations produced by current prosthetic implants are not like normal human vision. The devices produce “phosphenes”, which are spots of light in the visual field. These spots are generally white, but may have colour characteristics, and can have various spatial and temporal properties (Sinclair et al., 2016). The aim of a vision prosthesis is to use these spots to map out the visual scene, to allow people to identify objects and navigate. A simulated representation of phosphene vision is shown in Figure 25.4 but in reality the images are dynamic and are affected by factors such as phosphene fading (Stingl et al., 2013) and variations in phosphene appearance (Sinclair et al., 2016).
Hodgkin Lymphoma Associated Retinopathy: Report of a Case
Published in Ocular Immunology and Inflammation, 2022
Daphné Dedieu, Emna Bouayed, Antoine P. Brézin
One year later, the same ocular symptoms recurred with phosphenes in the right eye. This time there was no active inflammation detected in the anterior chamber or in the vitreous and no additional chorioretinal lesions. Concomitantly, a relapse of HL was diagnosed by 18Fluorodeoxyglucose positron emission tomography (PET) scan. The patient was treated by a second line of chemotherapy as well as by radiotherapy, which again led to a complete remission. Three years after the initial manifestations, the BCVA was 0.8 in the right eye and 1.0 in the left eye without ophthalmic symptoms. No active intraocular inflammatory manifestations were detected and the scarred chorioretinal lesions were unchanged. The OCT showed a thinning of the outer retinal layers with a rupture of the photoreceptors’ line and a peripapillary fibrosis. The electroretinogram also revealed a slight decrease in the amplitude of a and b waves predominantly on rods’ responses. The full visual field showed a nasal notch in the right side.
Neuromodulation beyond neurostimulation for epilepsy: scope for focused ultrasound
Published in Expert Review of Neurotherapeutics, 2019
Manish Ranjan, Alexandre Boutet, Sanjiv Bhatia, Angus Wilfong, Walter Hader, Mark R Lee, Ali R Rezai, P. David Adelson
Other authors have reported on the stimulatory role of FUS. Lee et al. [29] reported stimulation of the primary visual cortex (V1) with transcranial FUS using 270 kHz frequency ultrasound. The authors could demonstrate stimulation of the primary visual cortex (V1) with both electrophysiology and fMRI in human volunteers. Accompanying phosphene perception (i.e., positive stimulatory effect, in which a person experiences seeing light but without light actually entering the eye/visual system) was reported by the subjects following transcranial FUS. These phosphenes were associated with distinct changes on EEG and fMRI. The stimulation was only restricted to the local site of sonication but also specifically targeting networks of regions involved in visual and higher-order cognitive processes. In another series of experiments of low-intensity FUS, thalamic sonication in Yorkshire swine demonstrated modulation of neuronal circuits with a high spatial resolution (∼ 2 mm) and without tissue damage [30]. While there is a potential neuromodulatory role of FUS in epilepsy, further studies are needed prior to clinical translation. Such early studies do not provide sufficient understanding to assess the indications, efficacy of treatment, and longevity of the reversibly modulated epileptic pathways.
Self-monitoring of intraocular pressure in glaucoma
Published in Expert Review of Ophthalmology, 2019
In 1997, the pressure phosphene tonometer was invented with the intention that it be used for home tonometry. The Proview Eye Pressure Monitor (Bausch & Lomb, Rochester, NY), a spring-loaded tonometer with a 3.06 mm circular head, had the advantage that it could be used without anesthetic [25,26]. The device was applied to the globe through the upper lid and pressure applied until it produced a pressure phosphene visual phenomenon described as a dark circle surrounded by a bright halo. The patient performing self-tonometry was required to increase pressure on the eye until the pressure phosphene was seen and the device provided an IOP reading. The pressure phosphene device was cheap to produce, easy to use and was not affected by central corneal thickness, and it was reported in some studies to have a good correlation with GAT for pressures in the range of 10 to 28 mmHg[26]. However, many other studies disputed this and ultimately there was no consensus on its reliability [18,27–30]. Other drawbacks included doubt over the reliability of the pressure phosphene phenomenon; in particular, it was found that up to 31% of patients were unable to identify pressure phosphene. [18,25,28,31,32]