Biomedical subjects
Publications and source records attributed to J P Ary.
Scotomas associated with suppression amblyopia can appear or enlarge under binocular conditions. A device was designed to present an independent LED stimulus array to each eye while both eyes fixate together through beam splitters on a common background pattern. A computer-controlled field screening examination was designed to automatically plot suppression scotomas under binocular conditions.
Accurate assessment of visual function in infants and preverbal children is difficult because of the dependence on vision tests that require the patient's cooperation. In an attempt to resolve this problem, we evaluated pattern visual evoked potentials (PVEPs) obtained on infants under chloral hydrate sedation. Ten patients were studied--four with unilateral amblyopia, three with suspected amblyopia, and three without amblyopia. Patients with amblyopia showed robust and reproducible responses from the sound eye, while responses from the amblyopic eye were significantly diminished (amplitude ratio less than or equal to 0.63). The PVEP responses from patients without amblyopia were large in amplitude and symmetrical between fellow eyes (amplitude ratio greater than 0.9). In two eyes with normal vision, optically fogging the patterned stimulus image substantially reduced the PVEP response, establishing a sensitivity to pattern images rather than changes in the overall luminance. We have thus determined that the PVEP can be reliably obtained under chloral hydrate sedation and that these responses, like PVEP responses taken in the awake state, reflect the presence of amblyopia and image clarity. Use of the PVEP with chloral hydrate sedation may prove clinically useful for detecting amblyopia in uncooperative infants and children.
This study quantifies the amplitude variability of the pattern visual evoked potential (P-VEP) and compares this variability between the two eyes and between individual runs recorded in the typical clinical laboratory. Cooperative adults were studied in order to obtain measurements under optimal conditions. Average P100 amplitudes of 10 runs for one eye were essentially equal to average P100 amplitudes of the other eye, as were the variances. Mean amplitude ratio (the smaller amplitude divided by the larger amplitude) was 0.91. With a group mean P100 amplitude of 10.06 microV, standard deviation for intrasubject data was 1.84, and for intersubject data was 3.75. Therefore, most of the amplitude variability between the two eyes is due to run-to-run variability. A minimum of 3 runs (100 stimuli each) and an optimum of 5 runs should be recorded before making an evaluation.
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Visually evoked scalp potentials (VESP) have been recorded at 40 electrode sites from each of 3 subjects. Pattern appearance/disappearance was used for whole field and partial field stimulation. The data are displayed as equipotential maps. The topographical features of the equipotential maps show periods of stable organization followed by periods of relatively rapid change. The structure of the maps changes in a consistent pattern with the region of the retina stimulated; the first peak fits well within the framework of the cruciform model of striate cortex. The first and second peaks of the VESP appear to be caused by independent neural generators. The work reported in this paper shows major agreement with other authors and reconciles some points of disagreement between them.
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We assessed the effect of amblyopic suppression on the pattern visual evoked potential (P-VEP). Since anisometropic amblyopia is associated with the monofixation syndrome and a central suppression scotoma in the amblyopic eye, patients with this functional defect were used for the study. Five anisometropic amblyopes and four normal subjects were studied using the P-VEP test. A modified haploscope was used to present a pattern stimulus to the area of suppression. By comparing responses generated under monocular conditions (non-suppression) with monocular responses under binocular viewing conditions (suppression), we measured the effect of suppression on the P-VEP. Our results show that amblyopic suppression completely abolishes P-1 amplitudes in patients with large suppression scotomas; in patients with small suppression scotomas the P-1 amplitudes were greatly reduced. Rivalry in normals also caused a reduction in P-1 amplitudes, but to a much lesser degree than that associated with anisometropic suppression. Patients with significant amblyopia did not show a rivalry effect on the P-VEP. Because the P-1 wave of the transient P-VEP is thought to represent activity at the level of the striate cortex, our results indicate that suppression probably occurs at the striate cortex or lateral geniculate nucleus.