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Biomedical subjects

D H Zackon

Publications and source records attributed to D H Zackon.

12 recordsLinked to original sources
PubMed2001

Vigabatrin effect on inner retinal function.

OBJECTIVE: To determine the degree of electroretinal dysfunction in a group of patients taking Vigabatrin (VGB). Additionally, to investigate the role of cumulative dosage, the role of VGB alone or in combination with other anticonvulsants, and whether recent discontinuance of VGB affects electroretinal function as measured by the electroretinogram (ERG). DESIGN: Retrospective, comparative case series. PARTICIPANTS: Forty patients (18 male, 22 female) with a mean age of 35 years were studied as three groups: the VGB multitherapy group (n = 24) included those taking VGB with other anticonvulsants, the VGB monotherapy group (n = 9) included those taking VGB alone, and the off-VGB group (n = 7) included those who had discontinued VGB in the last 6 months. METHODS: Scotopic flash, photopic flash, and 30-Hz flicker ERG results were recorded according to the International Society for Clinical Electrophysiology of Vision (ISCEV) standard. The clinical electro-oculogram (EOG) results were recorded according to the ISCEV standard. MAIN OUTCOME MEASURES: Implicit time and amplitudes of the A- and B-waves of the flash and 30-Hz flicker ERGs were recorded. Summed amplitude of the first three oscillatory potential wavelets were recorded. The light-peak to-dark-trough Arden ratio of the EOG was evaluated. RESULTS: Although photopic ERG B-wave reduction was most frequent in patients in the VGB multitherapy group (48% of eyes), a significant number of eyes in all three groups had scotopic ERG B-wave reduction. The 30-Hz flicker ERG result was abnormally reduced in all three groups. There was no significant difference in the frequency of occurrence in ERG result abnormalities between the VGB monotherapy and VGB multitherapy groups. The EOG results revealed reduced Arden ratios in all three groups; however, there was a significantly lower frequency of EOG abnormalities noted in the off-VGB group (P = 0. 0373). There was no statistically significant relationship between the frequency of electrodiagnostic abnormalities and the duration of use or the total cumulative dosage of Vigabatrin in any of the three groups. CONCLUSIONS: These findings of scotopic ERG result abnormalities suggest that VGB alone has an effect on inner electroretinal function at the level of the Müller cell. Concomitant EOG abnormalities suggest a substantial effect of VGB on outer retinal function that may be reversible after cessation of VGB treatment.

4-Aminobutyrate Transaminase↗
PubMed1999

The temporal order judgment paradigm: subcortical attentional contribution under exogenous and endogenous cueing conditions.

The role of subcortical attentional processing was investigated under exogenous and endogenous cueing conditions. As retinotectal projections arise predominantly from the nasal retina i.e., temporal hemifield, subcortical attention should be distributed asymmetrically under monocular viewing conditions with a temporal hemifield advantage. We compared the results of monocular and binocular viewing conditions using a temporal order judgment (TOJ) paradigm. Subjects fixated a centrally located cross and two stimuli were presented with a variable onset asynchrony. Three experiments were conducted: no cue, exogenous cue and endogenous cue. Subjects reported which stimulus seemed to appear first. An effect consistent with subcortical processing was found under exogenous cueing conditions. No such effect was found under endogenous cueing conditions. We believe that subcortical attentional processing in response to an exogenous cue facilitates rapid shifts in attention towards environmental stimuli. We found no evidence for subcortical processing in voluntary directed attention and believe this process to be cortical in nature.

Adolescent↗
PubMed1999

Familial occurrence of pseudoexfoliation in Canada.

BACKGROUND: Genetic factors may play an important role in pseudoexfoliation syndrome. We describe the familial occurrence of pseudoexfoliation in Canadian families. METHODS: Probands with pseudoexfoliation were referred to a tertiary care glaucoma service in Ottawa because of a family history of pseudoexfoliation or glaucoma, or both. Probands and family members who agreed to participate underwent a systematic interview and eye examination. The pseudoexfoliation status was classified as affected, suspect or unknown based on preestablished criteria for the diagnosis of pseudoexfoliation and glaucoma. RESULTS: Thirty-four members of 10 families were assessed (18 affected, 2 suspect and 14 status unknown). Six families had two or more generations with pseudoexfoliation, and four families had one generation affected. There was a predominance of females among the affected subjects (17:1), and transmission in all cases appeared to be maternal. Eight of the families were of Irish/Scottish ancestry. Nine (50%) of the affected subjects had cardiovascular disease. Affected subjects tended to be older than suspects and those whose status was unknown (mean age 77, 67 and 55 years respectively). Seven subjects were affected unilaterally and 11 bilaterally. Affected subjects had moderate angle pigmentation in both eyes (mean +2.7, where 0 = no pigment and +4 = dense homogeneous pigment). The mean intraocular pressure in both eyes was higher for the affected subjects (23.1 [standard deviation (SD) 8.6] mm Hg) than for the suspects (16.8 [SD 6.1] mm Hg) and those of unknown status (16.8 [SD 2.9] mm Hg). An enlarged cup:disc ratio was seen in the affected subjects (mean 0.62). Eleven (61%) of the affected subjects had open angles on gonioscopy, and five had occludable angles and required peripheral iridectomy. Ten (56%) of the affected subjects were classified as having glaucoma, and 14 (78%) had evidence of cataract formation in at least one eye. INTERPRETATION: Pseudoexfoliation appears to be transmitted matrilineally, which raises the possibility of mitochondrial inheritance, X-linked inheritance or autosomal inheritance with genomic imprinting. A larger study of families with pseudoexfoliation is necessary to clarify the mode of transmission and to identify the gene(s) involved in the etiology of this disorder.

Adult↗
PubMed1997

Distinguishing subcortical and cortical influences in visual attention. Subcortical attentional processing.

PURPOSE: The purpose of the study was to investigate the role of subcortical processing in human visual attention. The midbrain contribution to visual attention is unclear. Although evidence exists for a subcortical attentional advantage in ocular motor tasks, such an advantage has not been shown in perceptual tasks. Because retinotectal projections arise predominantly from nasal retina (i.e., temporal hemifield), subcortical attention should be distributed asymmetrically for monocular viewing conditions with an advantage to the temporal hemifield. METHODS: To test for a subcortical attentional effect, the authors compared the results of binocular and monocular viewing conditions using the split priming motion induction paradigm. In this perceptual attention paradigm, priming cues are presented to the left and right of fixation followed by an instantaneously presented horizontal bar. As a result of attention to the priming cues, motion is perceived within the bar as it appears to draw in from the two lateral cues toward a central collision point. Asymmetrically distributed attention results in an asymmetry in the perception of motion within the bar, and thus the perceived collision point will be shifted away from the center. RESULTS: In two separate studies, one with and one without control of eye movements, the authors found significant differences between the results for monocular and binocular presentation. When the stimulus configuration is presented to the left eye, the perceived collision point is shifted toward the center consistent with a subcortical attentional effect. However, presentation of the stimulus configuration to the right eye yields the same results as those of binocular presentation. CONCLUSIONS: This pattern of results can be explained by a separate and additive interaction between cortical and subcortical attentional effects in the visual field. Dominance of the left visual field for cortical attention and dominance of the temporal visual field for subcortical attention act together when the initial priming cue occurs in the temporal (left) visual field of the left eye. However, these influences compete when the same stimulus configuration is presented to the right eye, where cortical attention predominates in the left visual field and subcortical attention predominates in the temporal (right) visual field.

Adult↗
PubMed1991

Ocular motor apraxia following cardiac surgery.

Ocular motor apraxia is characterized by a deficiency in the generation of voluntary saccadic eye movements despite the presence of spontaneous saccades. We report two cases of isolated ocular motor apraxia, both in children, that developed following cardiac surgery. Electro-oculography was done in one case and showed slow saccades and decreased pursuit gain. The authors review the neuroanatomic and neurophysiologic features relevant to supranuclear gaze mechanisms.

Apraxias↗
PubMed1987

Smooth pursuit during dose-related on-off fluctuations in Parkinson's disease.

Smooth pursuit was studied during predictable L-dopa dose-related "off" periods of morning akinesia and wearing off and during "on" periods in eight patients with idiopathic Parkinson's disease. Smooth pursuit gain was significantly reduced in patients during both on and off phases. Despite marked fluctuations between parkinsonism and periods of near normal skeletal motion, there were no changes in smooth pursuit gain. We conclude that unvarying paresis of smooth pursuit in Parkinson's disease signifies involvement of neural circuits that are distinct from the dopaminergic mechanisms that mediate the on-off phenomenon of somatic motor control.

Electrooculography↗
PubMed1984

Midbrain paresis of horizontal gaze.

Unilateral paramedian involvement of the midbrain tegmentum causes monocular paralysis of adduction in the ipsilateral eye, paresis of contralateral saccades in the opposite eye, and conjugate paresis of ipsilateral smooth pursuit. The adduction paralysis can be nuclear, or internuclear from a lesion in the medial longitudinal fasciculus. This distinctive midbrain syndrome of horizontal gaze paresis is exemplified by means of quantitative infrared oculographic, radiological, and neuropathological correlation in two patients with predominantly paramedian midbrain tumors involving the mesencephalic reticular formation and the oculomotor nucleus. Binocular paralysis of elevation provided evidence that one human oculomotor nucleus contains axons to both superior rectus muscles, as does the simian oculomotor nucleus. The midbrain tectum was spared. These pathophysiological correlations indicate that the mesencephalic reticular formation contains pathways that control contralateral saccades and ipsilateral smooth pursuit.

Blepharoptosis↗
PubMed1983

Tadpole-shaped pupils caused by segmental spasm of the iris dilator muscle.

Segmental spasms of the iris dilator muscle produce intermittent pupillary distortion. A study of 26 case histories (six previously reported and 19 reported for the first time) showed that the episodes are brief (lasting less than five minutes in 23 of 26 patients, less than two minutes in 18 patients, and less than one minute in eight patients) but can occur several times a day. The patients ranged in age from 24 to 48 years (the age of one patient was not known); five were men and 21 were women. Eleven patients had Horner's syndrome, four had Adie's tonic pupil, and eight had definite or probable migraine (another three had possible migraine). The episodes eventually stopped, leaving no serious sequelae. Focal application of phenylephrine produced a similar distortion in a normal human eye.

Adult↗
PubMed1982

Neuro-ophthalmology.

Ocular symptoms may indicate the presence of systemic or neurologic disease rather than simply local eye disease. Patients with such symptoms often present initially to the family physician. This article discusses important aspects of the neuro-ophthalmic examination that can aid the physician in identifying common neuro-ophthalmic disorders.

Aged↗
PubMedDate not supplied

Smooth pursuit in senescence. Effects of target acceleration and velocity.

Smooth pursuit responses to sinusoidal and triangular waveform targets were investigated in elderly and middle-aged subjects. The middle-aged pursued triangular targets with significantly lower gain than sinusoidal targets. In the elderly, pursuit gain was significantly lower than in the middle-aged under all target conditions. When all smooth eye movements at a constant frequency were correlated with varying target velocity, pursuit gain was uniformly reduced in the elderly, irrespective of target velocity up to 63 degrees/s or accelerations up to 395 degrees/s2. Within these limits, the steady-state gain of pursuit was depressed. At higher target accelerations having the same velocity range, smooth pursuit velocities were further reduced in the elderly. Senescent tracking is depressed by involvement of the steady-state gain element of the pursuit system at low target accelerations and by acceleration saturation at higher demands.

Adult↗
PubMedDate not supplied

Senescent saccades. Effects of aging on their accuracy, latency and velocity.

The effects of aging on horizontal saccades were investigated by infrared oculography in young, middle-aged and elderly normal subjects. Saccades were elicited in response to three target conditions: 1) predictable amplitude direct and timing; 2) unpredictable amplitudes and directions at regular intervals; and 3) unpredictably timed targets of predictable amplitude and direction. Peak velocities were significantly reduced in the elderly when target amplitude and direction were predictable. Latencies were prolonged in the elderly under all conditions. Saccadic accuracy was significantly decreased in elderly subjects; the amplitudes of primary saccades were reduced and hypometric saccades were frequent. The results indicate that the diagnosis of saccadic dysfunction in disease should be qualified by the age of the patient and by the target task.

Adult↗