Cerebral Visual Disturbances Research Articles

Low vision, Sequelae and Low Vision Rehabilitation in Retinopathy of Prematurity

Retinopathy of prematurity is one of the most important causes of blindness and low vision in childhood. In premature-born individuals, as well as retinopathy of prematurity, cerebral-induced visual disturbances are frequent and may result in low vision and blindness. In premature-born infants and children with or without retinopathy of prematurity, long-term eye and visual disturbances are more common than the term-born ones. Among these; myopia, refraction errors, strabismus, amblyopia, glaucoma, cataract, late retinal detachments, sensory and perceptual dysfunction, visual field defects, and cerebral visual disturbances can be seen. For this reason, life-long follow-ups of preterm born individuals are so important in terms of functional vision in the longterm.

Contralateral monocular dominance in anterior visual cortex confirmed by functional magnetic resonance imaging

PURPOSE: Although it is known that the damage to anterior striate cortex results in temporal peripheral visual field loss of the contralateral eye in patients with cerebral visual disturbance, the monocularity of anterior striate cortex has not been demonstrated in normal living humans. The aim of this study was to investigate whether this could be shown noninvasively using functional magnetic resonance imaging of the human visual cortex. METHODS: Eleven normal volunteers were studied with functional magnetic resonance imaging during alternating monocular visual stimulation using a 1.5 Tesla scanner. The data were motion corrected and spatially normalized to the standard brain. The monocular activation of the visual cortex was compared with the activation by the other eye. RESULTS: In the individual data analysis, contralateral eye dominance was always observed in the anterior striate cortex. In the group analysis from 11 subjects, the area with contralateral eye dominance was found in the most anterior part of primary visual cortex where the calcarine fissure merged with the parieto-occipital sulcus. CONCLUSIONS: This study shows that the contralateral eye dominance of anterior striate cortex can be detected noninvasively with functional magnetic resonance imaging during monocular visual stimulation. The finding confirms that the anterior striate cortex, where the monocular temporal crescent is represented, is primarily monocular, but the fact that greatest density of retinal ganglion cells and photoreceptors is in the nasal hemiretina must also be taken into account when interpreting these results.

Detection of pediatric visual defect

The clinical evaluation of children under one year of age suspected of blindness or severe visual impairment is discussed. Etiology of childhood blindness has shown a marked decrease of acquired causes. A marked increase occurs of the group of combined visually and generally handicapped children. This is due mainly to the increase in cerebral visual disturbances in cerebral palsies. Differentiation between visual handicap on one side and psychomotor handicap on the other side is difficult. Non visual stimulation of motor activities and observation of the level of development may be helpful. The important question to be answered is whether the actual visual capacity is sufficient for the stimulation of the development of the psychomotor potential.

The prevalence of cerebral visual disturbance in children with cerebral palsy.

Assessment of visual acuity using the visual acuity card procedure in 164 children with cerebral palsy revealed low visual acuity in 71 per cent. Results of ophthalmological examination were available for 74 of these patients, but could not explain adequately the low visual acuity of 36 of the 43 patients (84 per cent) assessed by both the acuity card procedure and other techniques. There is a high probability that cerebral visual disturbance is present in these patients. Awareness of visual disability when compiling a programme of visual and neurodevelopmental stimulation for children with cerebral palsy is essential.

Book Reviews

Book reviewed in this article: Tough Decisions: A Clasebook in Medical Ethics: By JOHN M. FREEMAN and KEVIN MCDONNELL Encounters with Children: Pediatric Behavior and Development: Edited by SUZANNE D. DIXON and MARTIN T. STEIN Cerebral Visual Disturbance in Infantile Encephalopathy: By Onno Van NieuwenhuizenDordrecht Drugs and Pregnancy: Human Teratogenesis and Related Problems, 2nd Edn.: Edited by D. F. Hawkins Neural Regeneration: Edited by F. J. SEIL, E. HERBERT and B. H. CARLSON

Neuro-imaging of cerebral visual disturbances in children.

The present study comprises the neuroradiological examination (computertomography++, magnetic resonance imaging) of 26 children--9 of them were premature, 16 were full-term and in one patient, no details of the pregnancy were known--all suffering from: a) visual disturbance, not caused by ocular disease or afflictions of the optic nerve b) infantile encephalopathy The examination revealed characteristic lesions of the retrochiasmatic part of the visual system. These consisted of white matter abnormalities located periventricularly and just below the striate area, and of grey matter abnormalities of the striate cortex. The demonstration of these abnormalities may advance the diagnosis of the visual handicap and may facilitate early adjustment of developmental stimulation.

Role of MRI scanning in the diagnosis of cerebral visual disturbance

Visual dysfunction as part of cerebral palsy may be due to lesions of the retrochiasmatic visual pathways. Cranial computed tomography can reveal conspicuous and characteristic abnormalities in most patients presenting with the condition; however, in some patients the abnormalities may appear so subtle on computed tomography that they can be easily overlooked or their true significance questioned. Magnetic resonance imaging has proved to be of great value in demonstrating the neuroanatomic anomalies underlying the visual handicap of this latter group of patients, allowing for early diagnosis and precise management.

38 STRUCTURAL ABNORMALITIES IN CEREBRAL VISUAL DISTURBANCES

Cerebral visual disturbances (c.v.d.). are caused by defective function of retrochiasmatic optic pathways (optic tract, lateral geniculate body, optic radiation, visual cortex). Morphological studies (computertomography-CT, magnetic resonance imaging-MRI) in patients suffering from c.v.d. due to perinatal hypoxicischemic brain injury reveal:I, at CT: a) pathological widening of posterior horns of lateral ventricles and irregularity of delineation of posterior horn walls, indicating loss of tissue of optic radiations; b) hypodensities of subcortical white matter of occipital poles, indicating white matter lesions and c) cortical lesions. II. at MRI: a) bilateral ischemic infarction of lateral geniculate bodies and b) demyelination of subcortical white matter of occipital poles. These findings are compatible with the neuropathological sequelae of hypoxic-ischemic encephalopathy (neuronal necrosis, periventricular leukomalacia). The consequences of the morphological abnormalities mentioned above to visual function can be demonstrated by functional studies (visual evoked potentials; VEP-mapping; optokinetic nystagmography; single photon emission computed tomography).

CT-scanning in children with cerebral visual disturbance and its possible relation to hypoxia and ischaemia.

The examination of computertomography (CT) scans of 20 patients suffering from 'cerebral visual disturbance' (CVD) as part of infantile encephalopathy, revealed conspicuous abnormalities, which could be divided into two main groups: (1) lesions of the optic radiations; and (2) lesions of the calcarine cortex. The pathophysiological mechanisms underlying these abnormalities suggest an important role of hypoxia and/or ischaemia in the etiology of CVD.