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Biomedical subjects

M J Doslak

Publications and source records attributed to M J Doslak.

10 recordsLinked to original sources
PubMed1989

Quantitative analysis of the insulating effect of silicone oil on the electroretinogram.

A model of the ERG focusing on the insulation effect of silicone oil replacing the vitreous was used to quantify the ERG. The electrical properties of the structures of the eye, the frequency content of the ERG and the percentage of the silicone oil along with the remaining vitreous were incorporated in the model. The result was that it was not until at least 50 per cent of the vitreous was replaced with silicone oil that there was a small reduction in the ERG. As more silicone oil was put into the vitreous cavity the ERG became smaller. If the replacement were large leaving a layer of vitreous 0.24 mm thick, little ERG would be measured even if the retina were functional.

Biomedical Engineering↗
PubMed1988

A theoretical study of the effect of silicone oil on the electroretinogram.

A model of the electroretinogram useful for determining volume conductor effects was used to determine quantitatively the postvitrectomy effect of silicone oil on the ERG. The electrical conductivities of the structures of the eye, the frequency content of the ERG, and the percentage of silicone oil along with the remaining vitreous were incorporated in the model. The result was that it was not until at least 50% of the vitreous was replaced with silicone oil that there was a small reduction of the electroretinogram; this reduction increased nonlinearly as the percentage of silicone oil in the vitreal cavity increased. According to the model, if the vitreous replacement were large, little, if any, of the ERG would be measured even if the retina were quite functional.

Electric Conductivity↗
PubMed1986

Eye movements of stutterers.

As a consequence of recent inquiries into the brainstem activity of stutterers, saccades and pursuit were evaluated in stutterers and their matched normals while silent and talking. No ocular motor instabilities or aberrations caused by speech were found. Saccadic latencies and gains for the stutterers were normal, but peak velocities were higher and durations were shorter. This finding is consistent with hypotheses of speech dysfluency proposed by others. The gains of these fast saccades were kept normal by an adaptive decrease in the duration of the neural pulse producing the saccade. It is proposed that these fast saccades are a result of increased excitatory input to the burst cells in the brainstem.

Adult↗
PubMed1984

A theoretical study of the effect of vitreous hemorrhage on the electroretinogram.

A bioelectric field model of the electroretinogram was utilized to help determine whether the presence of blood in the vitreous could alter its electrical conductivity enough to attenuate what would have been a normal ERG. The electrical conductivities of the structures of the eye and the frequency content of the ERG were incorporated in the model. The result was that the vitreous conductivity would have to be reduced to a value below that of whole blood in order for the ERG to be significantly reduced. A reduced ERG would be due to another cause(s) and might preclude vitrectomy. According to this model, blood in the vitreous has no significant effect on conduction of the ERG to the cornea.

Electric Conductivity↗
PubMed1980

Internuclear ophthalmoplegia: recovery and plasticity.

We studied refixational eye movements of a patient during the gradual resolution of an internuclear ophthalmoplegia (secondary to head trauma) in an attempt to determine the relative contributions of both medial longitudinal fasciculus (MLF) recovery and secondary central plastic changes. Adduction-refixational eye movements in the affected eye consisted of an initial fast (saccadic) portion followed by a slow drift toward the new intended eye position. The fast and slow components of the movements reflected, respectively, the pulse and step increases in neural innervation. Shortly after the traumatic insult, the affected eye exhibited low adduction gain (pulse gain 0.34; step gain 0.37) and slow saccades with peak velocities of 55% and durations of 278%, normalized for achieved, rather than intended, amplitudes. Several months later the pulse and step gains, peak velocities, and durations of the saccades improved to 0.81, 0.92, 87%, and 145%, respectively. The increased gains and faster velocity were accomplished by increases in the firing frequency of the pulse and step, reflecting recovery of MLF axons, rather than saccadic system plasticity, which would have resulted in increased duration of the saccadic pulse.

Adolescent↗
PubMed1979

A model of Alexander's law of vestibular nystagmus.

The observation that the amplitude of vestibular nystagmus grows as gaze is increased in the direction of the nystagmus fast phase and diminished with gaze in the opposite direction is known as "Alexander's law". We have developed an analog computer model to simulate Alexander's law in nystagmus secondary to dysfunction of a semicircular canal. The model utilizes relevant brainstem anatomy and physiology and includes gaze modulation of vestibular signals and push-pull integration to create eye position commands. When simulating normally functioning semicircular canals, the model produced no nystagmus. When simulating total impairment of the canal on one side with gaze directed maximally in the opposite direction, the model produced a large amplitude nystagmus with linear slow phases directed toward the affected side. As gaze was changed from far contralateral to ipsilateral, the nystagmus gradually diminished to zero. When simulating partial impairment of one canal, the nystagmus was smaller in amplitude and absent in ipsilateral gaze.

Brain Stem↗
PubMedDate not supplied

Alexander's law: a model and resulting study.

Recently we developed an analog model to simulate Alexander's law in nystagmus secondary to dysfunction of a semicircular canal. Alexander's law is based on the observation that the amplitude of the nystagmus grows with increasing gaze in the direction of the fast phase and diminishes with gaze in the opposite direction. To investigate the assumptions made in the model, we conducted quantitative experimental studies on the effect of gaze on caloric-induced nystagmus in human subjects. A weak stimulus (water at 26.5 degrees C and 240 ml/min) was administered for several minutes which caused the development of jerk nystagmus. Both the average slow phase velocity and frequency reached a steady state at about three minutes after the start of irrigation and remained stable until the flow of water was stopped. To investigate the effect of gaze, each subject was asked to hold gaze at various positions from center, to the right, to the left, and to repeat the cycle. Results indicated that the slow phase velocity of the nystagmus was greatest in the direction of the fast phase and decreased approximately linearly with gaze in the other direction in accordance with Alexander's law. Frequency was not a function of gaze. We speculate as to the biological advantages of the brainstem neural circuitry responsible for Alexander's law.

Adolescent↗