Retrochiasmal Visual Pathways Research Articles

Pediatric Homonymous Hemianopia

Homonymous hemianopia is a disabling condition caused by numerous lesions affecting the retrochiasmal visual pathways. Little is known about homonymous hemianopia in childhood. All patients seen in the Neuro-Ophthalmology Unit at Emory University with homonymous hemianopia (confirmed by Goldmann, Humphrey, or confrontation visual fields) between 1989 and 2004 were included. Demographic characteristics, clinical features, and evolution of the visual field defects were compared between the pediatric group (18 years of age or younger) and the adult group (older than 18 years). Among 852 patients with homonymous hemianopia, there were 81 children (86 homonymous hemianopias) and 771 adults (818 homonymous hemianopias). Formal visual field testing was obtained in 93% of pediatric cases and 96% of adults; a majority of patients in both groups were evaluated with Goldmann visual field testing. Demographic and visual field characteristics were similar in both groups. Significant differences were noted for the causative lesions and their location. Traumatic brain injury (34%) and tumor (27%) were the most common causes of homonymous hemianopia in the pediatric group, whereas infarction (63%), traumatic brain injury (12%), and hemorrhage (11%) were the most common causes in the adult group. Most lesions involved the optic radiations (37%), followed by the occipital lobes (26%), in the pediatric group, whereas occipital lobes (47%), followed by optic radiations (32%), were most commonly involved in adults. Approximately one third of the pediatric patients were seen in follow-up, and one third of these homonymous hemianopias spontaneously improved over the course of time. Of the 16 pediatric homonymous hemianopias evaluated within 1 month of onset of the cerebral disorder, 8 (50%) improved. Trauma and tumors are the most common cause of homonymous hemianopia in childhood. Although spontaneous improvement can be expected in approximately one third to one half of patients within the first few months, the recognition of homonymous hemianopia frequently is delayed in this population.

Homonymous hemianopias

To describe the clinical characteristics and clinical-anatomic correlations of homonymous hemianopia (HH). Homonymous hemianopia impairs visual function and frequently precludes driving. Most knowledge of HH is based on relatively few cases with clinical-anatomic correlations. The authors reviewed medical records of all patients with HH seen in their service between 1989 and 2004. Demographic characteristics, characteristics of visual field defects, causes of visual field defects, neuroradiologic definition of lesion location, and associated neurologic deficits were recorded. A total of 904 HH were found in 852 patients. A total of 340 HH (37.6%) were complete and 564 HH (62.4%) were incomplete. Homonymous quadrantanopia (264 HH, 29%) was the most common type of incomplete HH, followed by homonymous scotomatous defects (116 HH, 13.5%), partial HH (114 HH, 13%), and HH with macular sparing (66 HH, 7%). A total of 407 HH (45.0%) were isolated. Causes of HH included stroke (629 HH, 69.6%), trauma (123, 13.6%), tumor (102, 11.3%), brain surgery (22, 2.4%), demyelination (13, 1.4%), other rare causes (13, 1.4%), and unknown etiology (2, 0.2%). The lesions were most commonly located in the occipital lobes (45%) and the optic radiations (32.2%). Every type of HH, except for unilateral loss of temporal crescent and homonymous sectoranopia, was found in all lesion locations along the retrochiasmal visual pathways. Homonymous hemianopia is usually secondary to stroke, head trauma, and tumors. Although the characteristics of visual field defects can be helpful in lesion location, specific visual field defects do not always indicate specific brain locations.

Neuro-ophthalmology

Recent advances in neuro-ophthalmology have been made in both diagnosis and therapy. New discoveries in molecular genetics have resulted in the identification of abnormalities in the nuclear and mitochondrial genomes likely responsible for retinitis pigmentosa and Leber's hereditary optic neuropathy, respectively. Neuroimaging continues to broaden our diagnostic abilities in both optic nerve disease and lesions of the retrochiasmal visual pathways. The role of steroids in idiopathic optic neuritis has been clarified by the Optic Neuritis Treatment Trial. The optic nerve sheath decompression procedure has become a useful and effective adjunct in the management of visual loss secondary to pseudotumor cerebri, and is currently being evaluated as a potential treatment for anterior ischemic optic neuropathy.

Topographic mapping of electrophysiologic measures in patients with homonymous hemianopia

We analyzed electroencephalographic (EEG) activity and spatial distribution of the pattern-reversal visual evoked potential (PVEP) in 20 patients with unilateral lesions in the retrochiasmal visual pathways. Focal abnormalities that were consistent with lesion location were present in the topographically analyzed EEG or VEP of 85% of the patients, compared with a 70% detection rate for conventional analysis techniques. Quantitative analysis of spectrally analyzed EEG revealed focal abnormality in 7 patients whose conventional EEG was interpreted as either normal or diffusely slow. However, focal paroxysmal spikes present in the EEG of 1 patient were missed by EEG mapping, and a false localization of quantitative EEG abnormality contralateral to the lesion occurred in 1 patient. Topographic analysis of the PVEP was no more sensitive to retrochiasmatic lesions than conventional analysis of 2 lateral occipital electrodes. We conclude that topographic mapping is a valid technique in the detection of localized cerebral lesions.

Giant axonal neuropathy: visual and oculomotor deficits.

Giant axonal neuropathy, a generalised disorder or neurofilaments, presents as a chronic, progressive peripheral neuropathy in childhood. Evidence for central nervous system involvement is demonstrated in this study of four male patients with giant axonal neuropathy who had defective visual function and abnormal ocular motility. The visual system was studied by electroretinography, which showed normal retinal function, and by visual evoked potentials, which showed disease of both optic nerves and retrochiasmal visual pathways. The ocular motility disorder, studied by electrooculography, comprised defective pursuit, inability to maintain eccentric gaze with gaze paretic and rebound nystagmus, abnormal optokinetic responses and failure of suppression of the vestibulo-ocular reflex by fixation. These findings suggested involvement by giant axonal neuropathy of the cerebellar and brain stem pathways important in the control of ocular motility.

Homonymous hemianopia in multiple sclerosis. With report of bilateral case.

A patient with multiple sclerosis and bilateral retrochiasmal visual field defects is reported. Homonymous field defects are rare in multiple sclerosis despite the frequency of pathological involvement of the retrochiasmal visual pathways. A higher incidence might be found with a higher index of suspicion and careful visual field testing with qualitative confrontation technique. Other reasons for the infrequent clinical detection of retrochiasmal lesions are considered. Such lesions may exist without demonstrable defect. This may be explained by anatomical factors, for example, fibre arrangement, or physiological factors, such as, geniculate or retrogeniculate integration. Lesions producing demonstrable defects may be asymptomatic because they: affect only the peripheral field, are small scotomas that do not impair visual acuity, affect only one eye, or occur late in the course of disease when masked by optic nerve involvement.

OPTIC ATROPHY IN CHILDHOOD

An attempt has been made to determine the significance and outcome of optic atrophy as an apparently isolated entity in the pediatric age group. A follow-up study was made of 48 children who presented in early childhood with optic atrophy with no known cause and no obvious systemic or neurological disease. It was found that the prognosis for useful vision is in general favorable in this group of cases. However, the significant incidence of mental retardation and other neurological impairment was noted for those children who had manifested severely impaired vision under one year of age. There was no correlation between specific symptoms and the outcome of vision. The patients with idiopathic optic atrophy were compared with other patients who presented with optic atrophy without signs of systemic or neurological disease on initial examination but who were later found to have underlying disease. X-ray findings of enlargement of the optic foramina, deformity of the sella turcica, and suprasellar calcification or hyperostitic changes in the region of the optic foramen were found to be important differential diagnostic features, as was the presence of proptosis or visual field defects, reflecting involvement of the optic chiasm or retrochiasmal visual pathways. By the use of these features and certain laboratory determinations it was possible to separate the idiopathic group from patients whose optic atrophy was secondary to optic nerve and chiasm gliomas, other intracranial neoplasms, fibrous dysplasia, congenital syphilis, and orbital neurofibroma. Problems in the diagnosis and differential diagnosis of optic atrophy have been discussed.