Cortical Visual Loss
Vivek Lal in A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
The lateral geniculate nucleus is the terminus of the optic tract, whose fibers synapse in this nucleus with the neurons that give rise to the optic radiations. This nucleus is located in the ventro-postero-lateral thalamus. It has a retinotopic organization: the macula is represented in a dorsal wedge and the far periphery is ventral, while the inferior quadrant is medial and the superior is lateral. Two arteries supply it. The lateral choroidal artery, a branch of the posterior cerebral artery, supplies the middle zone (20) while the anterior choroidal artery, a branch of the internal carotid artery, supplies its medial and lateral aspects (21, 22). This blood supply is reflected in the classic hemifield defects from partial destruction of the lateral geniculate nucleus. A lateral posterior choroidal artery stroke causes a sectoranopia (Figure 20.3a), a wedge-shaped defect emanating from the central field that straddles the horizontal meridian (20). An anterior choroidal artery stroke produces an inverse sectoranopia (Figure 20.3b), defects adjacent to the vertical meridian in the upper and lower field that spare the zone around the horizontal meridian (21–23). Ultimately, the patient will develop a subtle partial optic atrophy, but the pupil light reflexes are normal.
Disruptions in physical substrates of vision following traumatic brain injury
Mark J. Ashley, David A. Hovda in Traumatic Brain Injury, 2017
The diencephalon is the brain region above the brain stem, and it sits deep in the midline between the cerebral hemispheres. It has two major components: the thalamus and the hypothalamus. The thalamus gates sensory input to the cerebral hemispheres and is vital for processing of the attentional system. Pertinent visually related subcortical nuclei located in the thalamus are the pulvinar and the lateral geniculate body (LGN). The pulvinar occupies 40% of the thalamic volume, is located in the posterior portion, and is considered an association nucleus involved in complex visual function. The lateral pulvinar is linked with the posterior parietal, superior temporal, and medial and dorsolateral extrastriate cortices8 as well as the superior colliculus.9 It plays a role in orientation and processing visual information in the dorsal stream. The inferior pulvinar is linked with temporal lobe areas concerned with visual feature discrimination and extrastriate areas concerned with higher analysis of vision. It also receives visual input from the superior colliculus9 in addition to direct input from the retinal ganglion cells.8 The LGN is the other thalamic visually related nucleus that is part of the afferent system. The LGN also receives projections back from cortical-related visual areas, indicating that higher cortical processing can influence visual perception at an earlier level.
Plasticity of Visual Cortex in Adult Primates
Jon H. Kaas, Christine E. Collins in The Primate Visual System, 2003
of each of the lateral geniculate nucleus layers that receive input from that eye. In cats, this would involve one of the two “A” layers, and one or more of the “C” layers, while in monkeys a monocular lesion would involve one of the two complete parvocellular layers (and its sublayers), one of the two magnocellular layers, and zones of koniocellular inputs. For simplicity, these layers for each eye are depicted in Figure 7.1 as a single layer, and the single layers for each eye are shown as adjacent rather than stacked, as they are in the lateral geniculate nucleus (LGN). The two layers (e.g., sets of layers) then project in matching patterns to primary visual cortex, V1. A monocular lesion obviously deprives each set of monocular LGN layers of all visual activation in a portion of the retinotopic map corresponding to the lesion, while the equivalent part of V1 is deprived of activation from only one eye. Obviously, the converging inputs from undeprived geniculate layers can compensate for the missing inputs. Matching lesions of both retinas, however, totally deprive both portions of LGN layers and a portion of V1. The basic experimental question addressed in the studies in cats and monkeys is what happens to the deprived neurons in the LGN and V1 after retinal lesions?
Evaluating the safety profile of focused ultrasound and microbubble-mediated treatments to increase blood-brain barrier permeability
Published in Expert Opinion on Drug Delivery, 2019
Dallan McMahon, Charissa Poon, Kullervo Hynynen
Effects of FUS+MB-mediated BBB treatments on behavior have been thoroughly assessed in a small number of studies utilizing non-human primates. McDannold et al. conducted a comprehensive study in rhesus macaques using a clinical-prototype MRgFUS brain system (ExAblate 4000, InSightec) to investigate the effects of a range of acoustic power levels and MB injection/infusion parameters. Behavioral responses were evaluated by observing activities of daily living and visual function and acuity after repeated FUS+MB treatments to the lateral geniculate nucleus (relay system for the visual pathway) and primary visual cortex. After five successive volumetric (~1 cm3) treatments targeting the primary and secondary visual cortices bilaterally over the course of 5–9 weeks, visual performance, visual acuity, motor skills, and species-specific behaviors were unaffected, although a few hypointense regions in T2*-weighted images were observed [16].
Potential mechanisms of retinal ganglion cell type‐specific vulnerability in glaucoma
Published in Clinical and Experimental Optometry, 2020
Anna Ym Wang, Pei Ying Lee, Bang V Bui, Andrew I Jobling, Ursula Greferath, Alice Brandli, Michael A Dixon, Quan Findlay, Erica L Fletcher, Kirstan A Vessey
The visual pathways between RGCs and the lateral geniculate nucleus of non‐human primates consists of layers that correspond to either the magnocellular or parvocellular pathway, much like the human lateral geniculate nucleus. Multiple studies using models of glaucoma in non‐human primates have shown that dysfunction of afferent parasol or midget cells leads to degeneration of the magnocellular or parvocellular pathway, respectively, as reviewed by Yücel et al.2003 Following two weeks of increased IOP, the magnocellular layers of the lateral geniculate nucleus with input from the glaucomatous eye appeared to contain fewer and smaller cells compared to the parvocellular layers.2009 However, equal reductions in magnocellular and parvocellular pathways were observed when examining metabolism, neurofilament and synapses in the lateral geniculate nucleus after almost one year of elevated IOP.1997
Can pattern electroretinography be a relevant diagnostic aid in amblyopia? – A systematic review
Published in Seminars in Ophthalmology, 2022
Andresa Fernandes, Nuno Pinto, Ana Rita Tuna, Francisco Miguel Brardo, Maria Vaz Pato
In animal studies, Yin ZQ et al.34 showed that changes in the visual cortex of amblyopic cats were physiologically related to changes in retinal cells. Heravian et al., de Souza Lima et al. and Parisi et al.8,9,32 justify the changes observed in PERG responses with changes in the functionality of neurotransmitters that occur in amblyopic eyes. According to these authors, the cells of the lateral geniculate nucleus that receive signals from the amblyopic eye are smaller and weaker when compared to the same cells of the normal eye. Allen B. et al. and Szigeti A. et al.35,36 also believe that the weaker signal produced by retinal cells may be associated with microstructural abnormalities that may depend on the depth of amblyopia. The functional loss of the LGN cells can be due to a weaker stimulus coming from the cells present in the retinal area, during the critical phase of the development of the visual system.10
Related Knowledge Centers
- Neuroanatomy
- Optic Nerve
- Optic Radiation
- Visual System
- Reticular Formation
- Thalamus
- Neuron
- Grey Matter
- White Matter
- Retinal Ganglion Cell