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Cortical Visual Loss
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
This relay ends at striate cortex, and beyond it information diverges into a large array of “extra-striate” visual regions. Lesions of these regions cause the second type of cortical visual impairment. Extra-striate deficits are not so typified by retinotopy, but instead show functional specificity, affecting certain types of visual processing but not others. Although there are many cortical regions involved in vision, they can be divided roughly into two main functional streams, a ventral and a dorsal pathway (1). The ventral pathway consists of medial occipitotemporal structures that are involved in processing color and form and in object recognition. For this reason, it is sometimes called the “What” pathway. The dorsal pathway refers to lateral occipitoparietal structures that are involved in motion processing and spatial functions such as attention, localization and targeting eye or hand movements. This is sometimes called the “Where” pathway, though some view the dorsal pathway's role more as preparing responses to the visual environment, an “Action” pathway (2). In this chapter, we follow this useful division, considering disorders of color processing or object recognition under the heading of ventral pathway disorders, and problems of motion or spatial processing as dorsal pathway disorders (3) (Figure 20.1).
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
These preliminary patient tests are most encouraging, because they provide further evidence of plasticity/learning curve of the visual pathway and demonstrate that epiretinal stimulation can be conducted in a retinotopic manner. While RGCs are located in closest proximity to the micro-electrode array and require less current, stimulation of these cells would require more image processing, complex stimulation patterns to account for lost retinal processing, and suboptimal, larger, and ill-defined percepts.38,39 It is more
Describe the retinotopic organisation of the visual pathway. Use an image in the left superior visual field as an example
Published in Nathaniel Knox Cartwright, Petros Carvounis, Short Answer Questions for the MRCOphth Part 1, 2018
Nathaniel Knox Cartwright, Petros Carvounis
The retinotopic mapping of the visual cortex is as follows: – the inferior hemiretina projects to the inferior lip of the calcarine sulcus– the superior retina is represented on the superior lip of the calcarine sulcus– the macula projects to the posterior 30% of both lips.
Location and stability of the preferred retinal locus in native Persian‐speaking patients with age‐related macular degeneration
Published in Clinical and Experimental Optometry, 2021
Abdollah Farzaneh, Abbas Riazi, Mehdi Khabazkhoob, Asgar Doostdar, Mehrnaz Farzaneh, Khalil Ghasemi Falavarjani
Three hypotheses – performance‐driven, retinotopy‐driven and function‐driven – have been proposed regarding central scotoma and location of PRL.16 Although there are some reasons and arguments in favour of each theory, none is yet proven. According to the function‐driven hypothesis, characteristics of PRL may be affected by daily activities including reading and writing. The location and stability of fixation may be different in native Persian‐speaking patients, who read and write from right to left, compared with English‐speaking subjects. All studies investigating the PRL have been conducted in countries where the reading and writing direction is from left to right or from top to bottom,16–23 and much less information is available about the location and status of fixation in native Persian‐speaking patients with AMD.
Altered Functional Connectivity of the Primary Visual Cortex in Adult Comitant Strabismus: A Resting-State Functional MRI Study
Published in Current Eye Research, 2019
Xiaohe Yan, Yun Wang, Lijuan Xu, Yong Liu, Shaojie Song, Kun Ding, Yuan Zhou, Tianzi Jiang, Xiaoming Lin
Furthermore, significant differences in the functional connectivity among brain regions were found between the strabismic and normal control groups by two-sample t-tests in a voxelwise manner. Compared with normal controls, ROI2 in the strabismic group had increased positive functional connectivity with the bilateral MOG/lingual gyrus/cuneus (BA19/18; Y = −75) (P< 0.001, corrected; Table 3 and Figure 2). ROI4 had increased positive functional connectivities with the bilateral MOG (BA19; Y = −84, Y = −81) and the right superior frontal gyrus/precentral gyrus/medial frontal gyrus (BA6/4/3; Y = −18) (P< 0.001, corrected; Table 3 and Figure 2). The findings without the cluster size threshold are shown in Supplementary Materials Table S1. In addition, the modern probabilistic maps of visual topography were used to compare with our results.30 There are several retinotopic visual areas overlapped with our current findings with ROI2, including V3d, hV4, VO1, LO1, V3v, V2d, VO2, V3b, V3a, V2v in the right hemisphere and V2d, V3d, V3a in the left hemisphere. There are several retinotopic visual areas overlapped with the current findings with ROI4, including hV4, PHC2, V3v, VO2, VO1, V2v, V3d, PHC1, LO1 in the right hemisphere and LO1, V3b, LO2 in the left hemisphere. The detailed regions overlapped are shown in Table 4.
NeurHistAlert 24
Published in Journal of the History of the Neurosciences, 2018
Frank W. Stahnisch, Jyh Yung Hor
This article reviews 15 years of contributions to visual pathway neurology by assessing the observations and experiences made by physicians and surgeons during the Russo-Japanese War and World War I. Both modern wars were characterized by the introduction of highly mechanized forms of conflict through machine guns, modern artillery, and the introduction of tank assaults. As the author shows, prominent neuroscientists such as Tatsuji Inouye (1881–1976), Gordon Holmes (1876–1965), and William Lister (1868–1944) used new morphological structuring aids, including refined retinotopic maps, for eliciting the lesions and defects in the primary visual cortex. These studies laid the groundwork of many later neurophysiological confirmations and explanations from clinical and electrodiagnostic approaches during and after World War II.