Biomedical subjects

M G Fendick

Publications and source records attributed to M G Fendick.

3 recordsLinked to original sources

PubMed1992

Visual remapping in infantile nystagmus.

The possibility that patients with idiopathic infantile nystagmus achieve spatial constancy by visual remapping was investigated by comparing subjective localization of flashed test targets to their absolute position in space and to their absolute position on the retina. Nystagmats first viewed a screen-stationary reference target that was followed by a test flash. A computer used eye movement feedback to precisely control the test flash position on the retina. All six nystagmats detected test flashes throughout their nystagmus cycle. For three nystagmats test flashes (total N = 48) were delivered to the same retinal locus that were, at different times, to the right and left of the reference target. More than two-thirds of such crossover stimuli were correctly located in space: when only those stimuli at least 0.5 deg from the reference were considered, two of three subjects correctly located all stimuli. Taken together these results argue that our subjects could see throughout the nystagmus cycle and shifted their visual map in synchrony with their nystagmus as an explicit means of avoiding oscillopsia.

Adolescent↗

PubMed1991

Visual-evoked cortical potentials in dissociated vertical deviation.

It is debatable whether chiasmatic misrouting of temporal optic-nerve fibers (similar to that found in ocular albinism) is also characteristic of dissociated vertical deviation. Pattern appearance, pattern reversal, and diffuse-flash, monocular full-field visual-evoked cortical potentials were recorded from albino and normal human subjects and subjects with dissociated vertical deviation. Pattern appearance was the most reliable stimulus for evaluating lateralization (albino-type misrouting) in adult albino patients, and diffuse-flash stimulation was almost as reliable in children. Pattern reversal was found to be an unreliable indicator. Lateralization was not evident among patients with dissociated vertical deviation, as determined by the three modes of stimulation. Our data supported earlier findings that pattern appearance is the most appropriate technique to detect lateralization. Our findings differed from those of previous reports in demonstrating that reliability of the lateralization phenomenon increases with age up to approximately 15 years. Pattern reversal stimulation was not reliable in patients with horizontal nystagmus.

Adolescent↗

PubMedDate not supplied

Visual acuity measurements by swept spatial frequency visual-evoked-cortical potentials (VECPs): clinical application in children with various visual disorders.

Previous studies have indicated that visual acuities of normal infants can be estimated with good accuracy using swept spatial frequency visual-evoked-potentials (VECPs). In this report we describe acuity measurements obtained with this technique from 304 examinations performed on 135 children having various visual disorders. When possible, two or more different stimulation frequencies (8, 12, 15 or 24 contrast reversals/sec) were used in each patient, and three to eight sweep VECPs were obtained from each patient under each simulation and recording condition. High correlation coefficients (0.94 - 0.96) between the acuity estimated on each patient from either the single sweep giving the best visual acuity (BSS) or from vector averages (VeA) of the EEG data obtained from several sweeps confirmed previous findings in normal infants. We also found high correlation coefficients among BSS recorded at different temporal frequencies (0.79-0.97) and among comparisons of BSS or VeA acuity to optotype visual acuity (0.6-0.89). Children with clinically undetectable optokinetic responses showed lower visual acuity estimated by BSS than those who demonstrated optokinetic nystagmus. We conclude that the sweep VECP is a valid method, giving estimates of acuity which correlate well with optotype acuity and correspond well to other clinical findings, and that it can be useful in the clinical management of nonverbal patients.

Child↗