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Visual-Evoked Potential in Neuro-Ophthalmology
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
The optic nerves form connection between retina and the brain. Light impulses stimulate the photoreceptors (rods and cones) which further synapse with the inner nuclear or bipolar layers; bipolar cells synapse further with the ganglion cell layer. The axons of the ganglion cell form the optic nerve. The two optic nerves joined at optic chiasma. The optic tract starts from the optic chiasma and terminates in the lateral geniculate body. The optic tract contains ipsilateral temporal and contralateral nasal retinal fibers. The fibers carrying impulses from upper part of retina terminate in the ventromedial segment and those from lower part terminate in the ventrolateral segment of geniculate body. The ipsilateral temporal and contralateral nasal retinal fibers terminate alternatively in six layers in lateral geniculate body. Lateral geniculate body neurons form optic radiation, which pass posteriorly to terminate in the striate cortex (area 17). The macular fibers occupy the larger portion of occipital lobe at the occipital pole in a wedge-shaped area. The upper half and lower half of the retinal fibers relay superior and inferior to the calcarine fissure, respectively (Figure 3B.1).
Homonymous Hemianopia
Published in K. Gupta, P. Carmichael, A. Zumla, 100 Short Cases for the MRCP, 2020
K. Gupta, P. Carmichael, A. Zumla
The optic nerve contains both the visual and pupillary fibres. The left and right optic nerves join at the optic chiasma and then where the visual fibres cross to join the uncrossed fibres to form the optic tract which travels to the geniculate body. The optic radiation arising from the geniculate body travels to the visual cortex of the occipital lobe.
Ophthalmic system
Published in Pankaj Desai, Pre-eclampsia, 2020
There are multiple explanations for the ophthalmic features in pre-eclampsia. One of these is peripheral, meaning that the cause is in the retina. The exudative retinal detachment is a rare cause (<1%) of visual loss in pre-eclampsia and eclampsia, produced by the involvement of the choroidal vascularisation.2 As is well known, the human retina is a multi-layered structure. The deepest layer of the retina carries on as the optic nerve. In normal non-diseased situations, an image is focused on the superficial layer of the retina. This transmits an electronic impulse down the succeeding layers to the optic nerve. This nerve carries the impulse to the brain. Here the impulse gets sorted out and overturned by 180 degrees. The result is that the human being “sees”.
The therapeutic effect of nano-zinc on the optic nerve of offspring rats and their mothers treated with lipopolysaccharides
Published in Egyptian Journal of Basic and Applied Sciences, 2023
Eman Mohammed Emara, Hassan Ih El-Sayyad, Amr M Mowafy, Heba a El-Ghaweet
Many studies demonstrated that injecting bacterial LPS into the optic nerve of rats induced optic neuritis (ON). ON is characterized by a disruption of the blood-brain barrier (BBB) and leukocyte infiltration, as well as unilateral visual loss, afferent pupillary deficiency, abnormal visual evoked potentials (VEPs), periocular or retro-orbital pain in conjunction with eye movement, astrocytosis, demyelination, axon degeneration and RGC degeneration [12]. RGC oxidative damage is caused by increasing reactive oxygen species (ROS), and it is associated with numerous diseases such as glaucoma, hereditary optic atrophy, ischemic optic neuropathy, Traumatic Optic Neuropathy and Optic Neuritis. LPS injections also increased the levels of inducible nitric oxide synthase, COX-2, interleukin-1β and TNFα mRNA levels as well as increased the production of retinal superoxide, decreased activity of superoxide dismutase 2 and activated the inflammasome. All previous findings have been associated with optic nerve damage [13].
Orbital abscess: 20 years’ experience at a tertiary eye care center
Published in Orbit, 2022
Md Shahid Alam, Varsha Backiavathy, Veena Noronha, Bipasha Mukherjee
Sight-threatening complications included optic neuropathy in 15 patients (44.12%), orbital apex syndrome in 4 patients (11.76%), central retinal occlusion, exposure keratopathy in two patients each (5.88%), and panophthalmitis in one (2.94%). Optic neuropathy was diagnosed based on the assessment of optic nerve function tests such as visual acuity, color vision, pupillary examination and fundus evaluation. Sight-threatening complications were seen in 80% (n = 12) of adults and 63.16%(n = 12) of children. Life-threatening complications were noted in four patients (11.77%), three in children and one in an adult. Cavernous sinus thrombosis was diagnosed in two patients (5.88%), epidural abscess and septicemia were seen in one (2.94%) each. The abscesses were located in the intraconal space in five (14.70%) patients, extraconal space in 26 (76.47%), while three (8.82%) had involvement of both the spaces with diffuse orbital involvement. The breakup of the locations of abscesses in the extraconal space was as follows, 11 in the superomedial space, seven in the inferior space, six in the superior space, four in the lateral space, and two in the superolateral space. Multiple abscesses were seen in seven patients, of whom three comprised the ones with diffuse involvement and the other four were multiple extraconal abscesses.
Non-Arteritic Anterior Ischaemic Optic Neuropathy with Progressive Macular Ganglion Cell Atrophy due to COVID-19
Published in Neuro-Ophthalmology, 2022
Bora Yüksel, Faruk Bıçak, Fatih Gümüş, Tuncay Küsbeci
Rho et al. reported the first case of non-arteritic anterior ischaemic optic neuropathy (NAION) following COVID-19 infection in a patient with diabetic retinopathy.11 NAION is caused by occlusion of the short posterior ciliary arteries resulting in partial or total infarction of the optic nerve head.6 Major risk factors include crowded optic discs, hypertension, diabetes mellitus, and hyperlipidaemia.11 The usual presentation is in the 6th-7th decades with sudden, painless vision loss and mostly inferior altitudinal visual field defects. Diffuse or sectorial hyperaemic optic disc swelling with a few peri-papillary splinter haemorrhages may be seen. The swelling gradually resolves and pallor develops 3–6 weeks after onset.12 The optic nerve damage is usually severe and irreversible, depending on the extent of the occluded arteries.6 The usual duration of mild COVID-19 symptoms is reported as two weeks.13 Here we report a diabetic patient who developed NAION on the 13th day after contracting COVID-19.