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Contrast masking and spatial frequency properties of contour interaction in normals and amblyopes
Published in Jan-Tjeerd de Faber, 28th European Strabismological Association Meeting, 2020
With smaller stimuli and in amblyopia however discrimination thresholds are affected much more than detection. Under these circumstances masking alone can not account for the contour interaction. Higher level mechanisms of visual processing may be involved. Again this result agrees with other studies where smaller stimuli were used to compare masking and contour interaction and significant differences were found (Chung 2001, Palomares (1999), Parkes 2001).
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
The ideal location of the prosthetic implant varies depends on the cause of vision loss. For example, if the photoreceptors are lost or damaged (as in the hereditary eye disease, retinitis pigmentosa), then the prosthesis could be implanted within the eye to stimulate the inner retinal neurons and produce a visual percept. This is ideal in order to utilise the visual processing power of the inner retina. On the other hand, if the eye itself was non-functional or missing (for example, after trauma), then a prosthesis could be implanted in the lateral geniculate nucleus, or directly into the visual cortex. These are technically more challenging and none are currently commercially available. It is important to note that the neural stimulation from visual prostheses is markedly different from normal neural signalling because the electrodes or photodiodes, being relatively large, are non-specific in the cell types they stimulate. For this reason, prosthetic vision is very different to natural vision and significant post-implant visual rehabilitation is required.
Anatomy for neurotrauma
Published in Hemanshu Prabhakar, Charu Mahajan, Indu Kapoor, Essentials of Anesthesia for Neurotrauma, 2018
Vasudha Singhal, Sarabpreet Singh
The occipital lobe is responsible for visual processing. The primary visual area (Brodmann’s area 17) receives input from the optic tract via thalamus. The secondary visual areas (Brodmann’s area 18,19) integrate visual information.
Dysfunction in macula, retinal pigment epithelium and post retinal pathway in acute organophosphorus poisoning
Published in Clinical Toxicology, 2021
Padmini Dahanayake, Tharaka L. Dassanayake, Manoji Pathirage, Anuradha Colombage, Indika B. Gawarammana, Saman Senanayake, Michael Sedgwick, Vajira S. Weerasinghe
Visual electrophysiological tests systematically evaluate the function of the specific stages of visual processing from the retina to the visual cortex. Few animal studies provide evidence of abnormalities in electroretinography (ERG) following acute as well as chronic exposure to fenthion, chlorpyrifos and fenitrothion which provide evidence of retinal involvement in OP poisoning [6–8]. Though animal studies show that some OPs elicit visual electrophysiological changes, the effects of acute OP poisoning on visual system of humans have not been systematically studied [9]. In this background, the aim of this study was to investigate the potential effects of acute OP insecticide poisoning on the function of retina and post-retinal visual pathways of victims of acute OP self-poisoning. We evaluated 1) the functional integrity of the photoreceptors and ganglion cells of the macula using pattern electroretinography (PERG); 2) the integrity of the RPE using electro-oculography (EOG) and 3) the conduction along the post-retinal visual pathways using pattern reversal visual evoked potentials (PR-VEP).
Effects of longstanding degraded auditory signal on visuospatial, visuomotor, and visual attention skills in adults with hearing loss
Published in Cochlear Implants International, 2021
Sneha V. Bharadwaj, Patricia L. Matzke, Denise Maricle
Future research could examine relationships between performance on visual tasks and participant variables in a larger cohort of individuals with hearing loss. Future studies should supplement behavioral data with electrophysiological and/or imaging data (e.g. Campbell and Sharma, 2016) in order to examine the consequences of long-term auditory deprivation on behavior as well as brain functions. Additionally, future studies should gather surveys or self-reports to increase our understanding of the strengths and challenges related to other sensory systems in daily activities in individuals with hearing loss. Given the findings of the current study, aural rehabilitation programs should screen visual attention skills in adults with hearing loss. Cognitive interventions and auditory training have been effective in improving visual processing speed, working memory and attentional skills in adults (e.g. Ferguson and Henshaw, 2015; Wolinsky et al., 2013; Spencer-Smith and Klingberg, 2015). Similarly, studies have shown that training improves processing speed leading to plastic changes in the brain (in terms of connectivity among brain regions) in healthy young adults (Takeuchi et al., 2011). Thus, clinicians working with adults who have hearing loss should explore efficacious intervention programs to address attention skills. Ultimately, it will be important to assess how improvements in visual attention translates to changes in daily activities such as driving, communication functions, reading, writing or other tasks performed in the central visual field that require sustained attention.
Advances in understanding the mechanisms of retinal degenerations
Published in Clinical and Experimental Optometry, 2020
Over the last 20-years, a great deal has been learned about how the retina processes information, largely by analysing the neurotransmitters expressed by different cell types and the neurotransmitter receptors that mediate neural communication.8 What has emerged is that the retinal communication is highly complex, involving a range of neurotransmitters, and neurotransmitter subtypes which collectively shape visual processing. An example of this complexity can be seen when considering how glutamate mediates information transfer from photoreceptors to bipolar cells. The neural effects of glutamate are mediated by the action of glutamate on different types of glutamate receptors – including the ionotropic receptors, α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazoleproprionic acid (AMPA), Kainate, N‐methyl‐D‐aspartate (NMDA) receptors, or by metabotropic receptors (mGluRs).