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A Rare Case of Cortical Blindness - a Case Report E.A. Ashok Kumar, Hanvitha Muppala. A rare case of cortical blindness - A case report. IAIM, 2021; 8(5): 59-66. Case Report A rare case of cortical blindness - A case report E.A. Ashok Kumar1*, Hanvitha Muppala2 1Professor, 2Post Graduate Department of General Medicine, Malla Reddy Institute of Medical Sciences, Hyderabad, India *Corresponding author email: [email protected] International Archives of Integrated Medicine, Vol. 8, Issue 5, May, 2021. Available online at http://iaimjournal.com/ ISSN: 2394-0026 (P) ISSN: 2394-0034 (O) Received on: 14-04-2021 Accepted on: 21-04-2021 Source of support: Nil Conflict of interest: None declared. How to cite this article: E.A. Ashok Kumar, Hanvitha Muppala. A rare case of cortical blindness - A case report. IAIM, 2021; 8(5): 59-66. Abstract Cortical blindness refers to loss of vision caused by bilateral occipital lobe lesions with presence of intact anterior visual pathway. Neurological visual impairment encompasses a broad spectrum of conditions. These include cerebral visual impairment, visual neglect, visual agnosia, various visual perceptual disorders, homonymous hemianopia, lack of facial recognition, delayed visual development and cortical blindness. Cortical blindness refers to loss of vision produced by lesions affecting geniculocalcarine visual pathways. Complete Cortical blindness is much less common than incomplete blindness. Cortical blindness is mostly due to cerebrovascular accident but also reported in pregnancy induced hypertensive encephalopathy, trauma, as result of MS exacerbation, post cardiac surgery, obstetric hemorrhage, MELAS, cerebral angiography, adrenoleukodystrophy, CNS angiitis and HIV-related progressive multifocal leukoencephalopathy. In this case report, we present a case of patient with cortical blindness due to bilateral occipital Infarcts. Key words Cortical blindness, Bilateral occipital infarcts. Introduction brain regions in which these are processed into The term “Cortical Blindness” describes the meaningful visual input such as brightness- partial or complete loss of vision resulting from a contrasts, colors, objects, faces. They are “blind” brain lesion. In this disorder there are no to the visual information that is not transmitted. ophthalmological causes and with normal pupillary light reflexes. With this type of visual Cortical Blindness can however also affect vision impairment the eyes can be fully intact, but the in total; this requires damage to both sides of the visual information cannot be transmitted to the brain, usually due to bilateral lesions of the striate cortex in the occipital lobes [1]. Cortical Page 59 E.A. Ashok Kumar, Hanvitha Muppala. A rare case of cortical blindness - A case report. IAIM, 2021; 8(5): 59-66. blindness is a part of cerebral blindness which is Exact epidemiological data is not available. defined as loss of vision secondary to damage to Studies have shown a high incidence of cortical the visual pathways posterior to the lateral blindness in patients of cerebral stroke in the geniculate nuclei [2]. With cortical blindness in range of 20 to 57% [8]. Cerebrovascular disease both halves of the visual field a person is really was the most common cause according to various completely blind, he/she cannot consciously studies, followed by surgery, particularly cardiac process visual input any longer, cannot identify surgery, and cerebral angiography [9]. or describe objects, cannot recognize faces, cannot read a text or reach for an item. Pathophysiology Knowledge of the visual pathway is important In the year 1895, Austrian neuropsychiatrist for the localization of lesions in cortical Gabriel Anton described patients with bilateral blindness. In cortical blindness, lesion lies in the occipital lobe lesions, who were completely blind striate cortex, and often the nearby areas of the but were unaware of their blindness leading to brain are also involved. confabulation [3]. Visual pathway Etiology The optic disc is the starting point of the optic Cortical blindness can affect both children and nerve. The optic disc does not contain any visual adults. In children, common causes include; receptors. It is the physiological blind spot. Congenital abnormalities of the occipital lobe, Fibers from the temporal Half of retina are cardiac arrest, status epilepticus, hypoxia or situated in the lateral half i.e. temporal half of the perinatal asphyxia, cerebral infarction, optic nerve while fibers from the nasal half of meningitis, encephalitis, subacute sclerosing retina are situated in the medial half i.e. nasal leukoencephalitis, hypoglycemia, uremia, half. Similarly, upper retinal fibers are present hydrocephalus, shunt malfunction, head trauma, superiorly and lower fibers are present inferiorly cardiac surgery, cerebral or vertebral in the optic nerve. The optic nerve extends from angiography , drugs (i.e., cyclosporin A and the retina to the optic chiasm and the length is steroids), acute carbon monoxide poisoning, and about 5 cm. It is conventionally divided into four the ictal state in occipital lobe epilepsy or portions- intraocular, intraorbital, postictal phenomenon [4]. intracanalicular, and intracranial. In adults, it is seen in lesions of the primary The optic nerve is covered by the layers of visual cortex of the occipital lobes secondary to meninges. The intraocular part is the optic disc multiple disorders including; Stroke, Cardiac wherefrom the intraorbital portion starts leading embolism, Head trauma, Occipital lobe epilepsy, to the intracanalicular portion as the nerve Hyponatremia, Severe hypoglycaemia, traverses the optic canal. Then the two optic Creutzfeldt-Jacob disease, Infection e.g. HIV, nerve exit from the optic canals and form the Eclampsia, MELAS (mitochondrial myopathy, optic chiasm where temporal hemiretinal fibers encephalopathy, lactic acidosis, and stroke-like continue ipsilaterally and nasal hemiretinal fibers episodes),cardiac surgery, cerebral angiography, decussate and join the opposite optic tract. The IV contrast medium. Rarely, transient cortical tracts extend from the chiasm to the lateral blindness can be caused by Infective endocarditis geniculate body (LGB). Afferent fibers from the or Hypertensive encephalopathy, Posterior pupil leave the tract just anterior to the LGB. The reversible encephalopathy syndrome (PRES) [5, visual afferents synapse in the LGB and second- 6, 7]. order neuron starts as geniculocalcarine pathways (optic radiation) and terminate in the Epidemiology calcarine cortex of the occipital lobe. The primary visual cortex (V1) lies in the Page 60 E.A. Ashok Kumar, Hanvitha Muppala. A rare case of cortical blindness - A case report. IAIM, 2021; 8(5): 59-66. Brodmann’s Area 17. Area 18 (V2) also known majority of cases, however, central vision, as the parastriate or parareceptive area, receives including the foveal representation, remains and interprets impulses from Area 17. The intact because of the blood supply of the peristriate or perireceptive cortex, Area 19 (V3, occipital pole. The fovea is generally represented V4, V5) has connections with Areas 17, 18, and in the occipital pole and it receives its blood with other portions of cortex. supply from the middle cerebral artery along with the branches of the posterior cerebral artery. The anterior choroidal artery and Because of this dual blood supply, stroke causing thalamoperforators from the posterior cerebral the complete destruction of V1 is extremely rare. artery (PCA) supply the optic tract. Optic This preservation of central vision is very radiation is supplied by the middle cerebral important for rehabilitation. Another peculiarity artery (MCA) and the occipital lobe is primarily that can be seen in Cortical blindness patients is supplied by the PCA. The occipital lobe also 'blind sight' where an individual can perceive receives supply from the MCA. coarse flickering movement in the blind field. This is due to preserved unconscious visual History and physical examination processing abilities in the individuals because of To make a proper diagnosis and to determine the the heterogeneity of damage to V1. Other aetiology of Cortical blindness, proper history features of visual cortex lesion include Anton should be elicited, like birth history, antenatal syndrome, Riddoch phenomenon, and formed history, addictions, drug history, hypertension, visual hallucinations. diabetes, palpitation, fever and any history of head trauma. A complete neurological and Anton syndrome: It is also known as visual ophthalmological examination should be done. anosognosia when a person cannot see but An important thing to remember is that pupillary always denies the blindness even with clear light reflex remains intact in cortical blindness, evidence of blindness. These individuals often and extraocular movements will be normal. try to walk through the closed door or wall and in There is no relative afferent pupil defect (RAPD) the process of denial they take help of in cortical blindness. confabulation. It occurs due to lesions in the V1. There may be clinical features depending on the Riddoch phenomenon: This is also known as location of the lesion. Lesion in temporal lobe statokinetic dissociation. Here patients can only causes acute disturbance in memory, particularly perceive moving objects in the blind field, not if it affects the dominant lobe. Posterior cerebral the static ones [12]. Patients may not perceive artery occlusion may produce visual color or details of the moving objects except the hallucinations of
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