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Biomedical subjects

C Boylan

Publications and source records attributed to C Boylan.

16 recordsLinked to original sources
PubMed1990

Presaccadic spike potential with vertical saccades.

Presaccadic spike potentials were recorded from four electrodes placed around the eyes for 20 degree vertical saccadic eye movements. Twenty upward and 20 downward saccades were recorded using electro-oculography and the spike potentials back-averaged from the start of the eye movement. Separate average waveforms were obtained for upward and downward saccades. The onset of the spike was between 17.3 and 6.8 ms before the start of the saccade with downward saccades having earlier onsets than upward saccades. This difference was only significant in the right eye (P less than 0.025). The peak occurred between 3.4 ms before to 5.2 ms after the start of the eye movement and was earlier with downward saccades. This was only significant in the right eye (P less than 0.025). The onset to peak amplitude measured between 15.9 and 42.3 microV with no statistical difference between upward and downward saccades. It was found, however, that the electrodes placed below the eyes recorded larger amplitudes for upward saccades than the other electrode-recording positions (right eye P less than 0.05, left eye P less than 0.025). A second component to the spike potential waveform was observed in many of the recordings and a possible origin of this component due to eyelid activity is hypothesized.

Adult↗
PubMed1989

Presaccadic spike potentials with large horizontal eye movements.

Presaccadic spike potentials were recorded from electrodes at the inner canthus and below the eye in 10 normal subjects for a range of horizontal saccades (5 degrees, 10 degrees, 20 degrees and 40 degrees). An eye movement trace was recorded for 20 abducting and 20 adducting saccades to determine the beginning of the saccade, and the spike potential back-averaged from this point. The latencies of the spike potential onset and peak were found with respect to the start of the eye movement and the amplitude from the onset to the peak was measured for each saccade size. The latency values remained constant throughout the range of eye movement sizes, although adducting saccades showed an earlier onset and peak latency than abducting saccades. The amplitude data, however, showed a definite relationship between saccade size and spike potential amplitude, with a significant increase in the amplitude for saccades between 10 degrees and 40 degrees (inner electrode abduction, lower electrode abduction and adduction P less than 0.01; inner electrode adduction P less than 0.05). A possible explanation of this increase in amplitude is hypothesised from a computer model of the action potential activity that may occur in the extraocular muscles before an eye movement.

Action Potentials↗
PubMed1989

Presaccadic spike potential with congenital lateral rectus palsy.

Presaccadic spike potentials were recorded with 20 degrees horizontal eye movements in a subject with a congenital left lateral rectus palsy. Electrodes at the inner and outer canthi recorded the eye movements and an electrode below the eye recorded the presaccadic spikes. The responses to 20 abducting and 20 adducting saccades were back-averaged from the onset of the eye movement with the wave forms for abduction and adduction averaged separately. Recordings were made from each eye under 2 conditions: firstly with the eye from which the spikes were being recorded fixating and secondly with the eye from which the spikes were not being recorded fixating. In each case the non-fixating eye was occluded throughout. Recordings were made with eye position monitored initially in the eye from which the spikes were recorded and repeated with eye position monitored in the other eye. Results show that spikes could be recorded during abduction and adduction movements of both eyes but only if eye position was monitored in the right eye. Using the left eye as position monitor gave very broad low amplitude spikes. When eye position was monitored in the right eye the spikes recorded during abduction of the left eye had a low amplitude compared to those recorded during right eye abduction; right eye adduction spikes were also of low amplitude. A possible explanation for these findings and their implications on future recordings in pathological cases are discussed.

Action Potentials↗
PubMed1989

Changes in the presaccadic spike potential with age.

Presaccadic spike potentials were recorded from an electrode below the eye to 20 degrees horizontal saccades in 2 groups of 10 subjects; a young group with a mean age of 26 years and an old group with a mean age of 77 years. The onset and peak latencies, relative to the beginning of the eye movement, and the onset-peak amplitudes were measured for abduction and adduction movements separately. There was no significant difference in the onset or peak latencies of the 2 groups with either abduction or adduction. The amplitude, however, was significantly greater in the young group with both abduction (P less than 0.01) and adduction (P less than 0.025). Possible explanations of these results are given and the implications of the findings on the investigation of presaccadic spike potentials in both normal and pathological subject groups are discussed.

Adolescent↗
PubMed1989

Computed extraocular muscle activity during blinks.

The rotations and retractions of the eyeball due to co-contraction of the extraocular muscles are investigated using a model of the mechanics of the orbital plant. The hypothesis that the rotational movements are secondary to globe retraction is not supported.

Blinking↗
PubMed1989

Effect of saccade size on presaccadic spike potential amplitude.

Presaccadic spike potentials were recorded from electrodes placed at the inner canthus and below the eye in ten normal subjects. The responses to twenty abducting and twenty adducting saccades were back-averaged from the beginning of the eye movement, and separate waveforms were obtained for saccades of 20 degrees, 10 degrees, 7.5 degrees, 5.0 degrees, and 2.5 degrees. The spike onset and peak latencies relative to the beginning of the eye movement and the onset-peak amplitudes were measured. Throughout the range of saccade sizes, the onset and peak occurred earlier with adduction than with abduction, but there was no consistent change in the latency values with saccade size. The amplitude, however, showed an increase with saccade size up to movements of 10 degrees, although statistical analysis showed that these amplitude changes were not consistently significant. Comparison of the 20 degrees saccades to the 10 degrees saccades and the 10 degrees saccades to the 7.5 degrees saccades revealed no statistically significant differences in amplitudes. The difference between the 7.5 degrees and the 5 degrees saccades, however, was statistically significant (P less than 0.05) but only at the inner electrode with abduction; comparison of the 5 degrees and 2.5 degrees results showed a significant difference (P less than 0.01) at the inner electrode with both abduction and adduction. Comparison of the 7.5 degrees and the 2.5 degrees showed a significant difference (P less than 0.01) at both electrode sites with abduction and adduction. These findings are discussed with respect to the previously suggested origin of the spike potential and the choice of the recording electrode site.

Action Potentials↗
PubMed1988

Presaccadic spike potential to horizontal eye movements.

Presaccadic spike potentials prior to 20 degrees horizontal eye movements were recorded from 4 electrode sites around the eye with Pz as reference. The technique of back-averaging from the onset of the saccade was used and separate wave forms were obtained for abducting and adducting movements. The spike onset began between 12.0 and 4.4 msec before the beginning of the saccade with a significantly earlier onset with adduction (right eye P less than 0.001, left eye P less than 0.025). The peak occurred between the onset of eye movement and 7.8 msec after the beginning of the movement; the peak also occurred significantly earlier with adduction (right eye P less than 0.01, left eye P less than 0.01). The amplitude of the onset to peak measured from 32.2 to 47.0 microV with greater amplitudes on adduction compared to abduction although the differences were not statistically significant. Several of the traces also showed a later smaller component, after the main onset-to-peak complex, that has not been previously reported.

Action Potentials↗
PubMed1988

Normal visual pathway routing in dissociated vertical deviation.

Flash visually evoked cortical potentials have been recorded in three groups of age- and sex-matched subjects; one comprised of subjects with dissociated vertical deviation, one comprised of subjects with oculocutaneous albinism and one group of controls. The latency of the major positive (P2) component did not show statistically significant contralateral lateralization on monocular stimulation in either the dissociated vertical deviation group or the control group. Contralateral lateralization was found in the albino group at a statistically significant level (P less than 0.01). It is concluded that subjects with dissociated vertical deviation do not possess the typical albino optic pathway misrouting that has been reported.

Adolescent↗
PubMed1987

Excursion tests of ocular motility.

Three alternative excursion tests of ocular motility have been compared. A computer model of the mechanics of the extraocular muscles has been used to estimate the tensions developed by the muscles in these tests. On the basis of these calculations we recommend the transverse test in which the positions of the eyes are observed as they track a target moving from the right to the left with a fixed elevation and a fixed depression.

Computer Simulation↗
PubMed1986

Visual evoked cortical and subcortical potentials in human albinos.

Albinism is a congenital condition in which hypopigmentation occurs. In addition to this abnormality there is a misrouting of the optic nerve fibers, with some fibers from the temporal retina following a crossed route at the chiasma and terminating in the contralateral cortical hemisphere. This contralateral preponderance of fibers from each eye should be recognizable from recording the visual evoked cortical potential over each hemisphere on monocular stimulation. Such a technique should produce evidence of responses of either increased amplitude or shorter latency over the contralateral hemisphere. Twenty-five human albinos (twenty-three oculocutaneous, two ocular) have been examined. Pattern appearance-disappearance visual evoked cortical potentials were used, but only on bioccipital derivations did these show clear lateralization. With the flash response the P2 component has a consistently shorter latency over the contralateral hemisphere to the eye stimulated. The visual evoked subcortical potential shows contrasting lateralization. The implications of these findings are discussed.

Adolescent↗
PubMed1986

Visual acuity and the flash visually evoked cortical potential in albinos.

The flash visually evoked cortical potential (VECP) was recorded in 18 human albinos. In some individuals P2 (latency 100-120 msec) formed the major component while in others P1 (latency 60-80 msec) was the largest component and dominated the response. The relative amplitude of P1 compared to P2 was calculated, and the results compared to the levels of monocular Snellen Visual Acuity measured. A relationship was found such that the greater the amplitude of P1 compared to P2, the lower the level of acuity. (Group 1: rs = -0.509, P less than 0.05. Group 2: rs = -0.536, P less than 0.05).

Adolescent↗
PubMed1985

Lateralisation of the flash visually evoked cortical potential in albino babies.

Flash VECPs have been reported in 3 albino babies ranging in age from 1 to 7 months. The responses were dominated by a large positive component preceded by an earlier negative. The amplitude of this positive component measured from the peak of the preceding negative wave had a greater amplitude over the contralateral hemisphere on monocular stimulation indicative of the misrouting present in the albino visual system.

Albinism↗
PubMed1984

Lateralization of the flash visual-evoked cortical potential in human albinos.

Investigations were undertaken to determine which particular components of the flash visual-evoked cortical potential (VECP) lateralize on monocular stimulation in human albinos. Our results demonstrate that only the major positive component shows clear lateralization. Statistical analysis revealed that the latency lateralization was significant (P less than 0.001) while the amplitude lateralization was not.

Adolescent↗
PubMedDate not supplied

Calculating nursing turnover in NSW.

A study of nursing staff turnover is being carried out by the Nursing Research Team from the Riverina-Murray Institute of Higher Education for the New South Wales College of Nursing and the New South Wales Department of Health. The general aim of the study is to provide information about the annual rate of loss of registered nurses from public hospitals and licensed private hospitals in NSW. This paper provides background details about the project and recent attempts to understand the problem of nursing staff turnover. Brief mention is made of Australian and overseas literature and recent calls for methodological and conceptual precision in calculation nursing turnover. Reference is made to 'Nursing Turnover Indices' and other statistical descriptors used to guide this research.

Databases, Factual↗