Retrochiasmal Lesions Research Articles

Steady-state and transient visual evoked potentials in clinical practice.

The electrophysiological analysis of visual evoked responses is a powerful tool for the study of visual function. The combined application of pattern-reversal transient visual evoked potentials, critical frequency of photic driving, and visual evoked spectrum array has enhanced the reliability and the yield of these tests for the diagnosis of visual dysfunctions. Prechiasmatic and retrochiasmatic lesions are characterized by different abnormalities. Prechiasmatic lesions often can be further differentiated into retinal and optic nerve lesions by the simultaneous recording of retinal and cortical potentials.

Visual evoked potential diagnosis of field defects in patients with chiasmatic and retrochiasmatic lesions.

Visual evoked potentials were studied in 18 patients with visual field defects assessed by perimetry. Stimuli were reversing checkerboard and grating patterns of 13', full field and hemifield. Two reversal rates were studied: 1 Hz (transient VEPs) and 8 Hz (steady-state VEPs). Using monocular hemifield stimulation the "paradoxical lateralisation" of transient but not of steady-state VEPs was confirmed. Diagnostic yield was 90% using transient, but less than 20% using steady-state stimuli.

Visual evoked potentials to hemifield pattern stimulation in the diagnosis of retrochiasmatic lesions : Y. Kuroiwa (Hamamatsu, Japan) and G.C. Celesia (Madison, WIS, USA)

Visual evoked potentials to hemifield pattern stimulation in the diagnosis of retrochiasmatic lesions : Y. Kuroiwa (Hamamatsu, Japan) and G.C. Celesia (Madison, WIS, USA)

Visual evoked potentials with hemifield pattern stimulation. Their use in the diagnosis of retrochiasmatic lesions.

We measured several parameters of cortical potentials evoked by visual stimulation to produce a profile suggestive of retrochiasmatic lesions. Characteristic abnormal responses included (1) very low amplitude or absent transient visual evoked potentials (T-VEPs) after stimulation of the affected hemifield, (2) reversal of normal pattern amplitude of the T-VEP distribution after stimulation of the affected hemifield, (3) abnormal lateral occipital ratio, (4) absent or very low amplitude steady-state VEPs after stimulation of affected hemifield, and (5) abnormal midoccipital ratio.

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.

Visual field defects after missile injuries to the geniculo-striate pathway in man.

Visual fields (defined by detection thresholds for moving and stationary targets) were examined in 10 cases of homonymous field defects due to retrochiasmal lesions. Using the Tubingen Perimeter, results of multiple perimetric methods could be compared quantitatively at identical retinal areas. The principal finding was one of thorough-going association of deficits: no instances of selective impairment of motion detection, flicker resolution, or regional dark adaptation were encountered. Pupillary reactivity to low-intensity light was depressed in areas of homonymous scotoma, as long as care was taken to avoid stimulation of relatively more intact regions of the visual field by scattered light. In the only case showing extreme difficulties in visual recognition (“agnosia”) for faces and objects there were unusually severe reductions in differential light detection thresholds, and in all other “elementary” visual functions. One half of the cases showed small homonymous scotomata with a sharp decrease of light sensitivity. They were often located in a perifoveal region that was otherwise normal. Field defects bordering on the midvertical meridian followed this meridian closer and tended to have steeper borders than those bordering on the midhorizontal meridian. Sparing of foveal vision (averaging 1.5°) was the rule but the spared region had reduced sensitivity. “Splitting” of the fovea was found in one case. Incongruence of homonymous field defects was greater for peripheral defects than for those near the center of the field; usually nasal fields showed larger defects than temporal. This tendency was enhanced by the sparing of parts of the monocular crescent in three cases.