Biomedical subjects

J D Morrison

Publications and source records attributed to J D Morrison.

At least 37 records · Page 2Linked to original sources

PubMed1989

Abnormality of the pattern electroretinogram and pattern visual evoked cortical response in esotropic cats.

In six 3-week-old kittens, the tendon of the lateral rectus muscle of one eye was sectioned under anaesthesia in order to induce an esotropic (nasally-directed) squint. At maturity, the pattern electroretinogram (PERG) and pattern visual evoked response (PVER) were recorded under anaesthesia to phase-reversal at 1.67 Hz of a 0.5c/deg square wave grating pattern of 75% contrast. Refraction was determined by retinoscopy and confirmed by recording the PERG for different trial lenses. The amplitude and time-to-peak of the PERG and PVER were compared between operated and unoperated eyes, and with the responses of one normal and two sham-operated cats. With stimulation of the operated eye, the amplitude of the PVER was consistently reduced by 50% compared with the non-operated eye, confirming that the cats had become amblyopic as a result of the squint. While the appreciable inter-eye variations in the amplitude of the PERG of the normal and sham-operated cats precluded identification of a change in the esotropic cats, there was a consistent prolongation of the time-to-peak of the PERG by 50% with stimulation of the operated eye. This result is consistent with a retinal component to strabismic amblyopia.

Amblyopia↗

PubMed1989

The effects of 0.025% hyoscine hydrobromide eyedrops on visual function in man.

Instillation of three drops of 0.025% hyoscine hydrobromide into one eye at 5 min intervals caused a mydriasis and cycloplegia of rapid onset and of 4-6 days' duration; this was similar to the previously reported actions of concentrations of up to 0.5%. After refraction for the working distance of the experiments, contrast sensitivity to stationary oscilloscope-generated grating patterns of 10 and 20 c/deg was unaffected despite the mydriasis. Also, contrast sensitivity to laser interference fringes of 10 and 20 c/deg observed in the Maxwellian view, in which the effects of the ocular media are bypassed, was unaffected. Contrast sensitivity to a 3 c/deg phase-reversed grating pattern was, however, transiently reduced by 40% after hyoscine. A second series of experiments showed a deleterious effect of hyoscine on contrast sensitivity to both stationary and phase-reversed grating patterns of 2, 3 and 5 c/deg while contrast sensitivity at 10 c/deg was not consistently affected. These results were explained by a direct deleterious action of hyoscine at the level of the retina, specific to channels that detect low spatial frequencies.

Accommodation, Ocular↗

PubMed1989

The pattern visual evoked cortical response in human ageing.

The N1, P1, N2 and P2 components of the pattern visual evoked response (PVER) have been recorded to the onset of presentation of a sinusoidal grating pattern of 3 and 8 cycles/deg in groups of young (15-34 years) and old (53-94 years) subjects. The negative components were taken to arise from striate cortex and the positive components from extrastriate cortex. For grating contrasts of 3-40%, the time-to-peak of the N1, P1 and N2 components, but not the P2 component, increased with age while the amplitude and rise time showed no consistent changes. Comparisons between 3 and 8 cycles/deg revealed a longer time-to-peak of N1 and P1 at 8 cycles/deg within the young group though not within the old group, i.e. an additional increment in the time-to-peak had occurred at 3 cycles/deg with ageing. This was also reflected for grating contrasts which were multiples of each individual's contrast threshold, irrespective of age. Now, the time-to-peak of N1, P1 and N2 was similar in young and old groups at 8 cycles/deg. At 3 cycles/deg, however, the time-to-peak was still longer in the old group, though the intervals between components were similar to those of the young group. This suggested the requirement for a further increment in contrast to make the time-to-peak similar, due to a selective loss of sensitivity in ageing within the low-spatial-frequency channels which are additionally sensitive to temporal modulation. Thus, it appeared that, by incrementing the stimulus contrast by the appropriate amount, the PVER of the old group could be made to resemble that of the young group. These results are consistent with the occurrence of neural changes during ageing in the retino-geniculate pathway prior to the visual cortex.

Adolescent↗

PubMed1989

Use of the Femurett adjustable prosthesis in the assessment and walking training of new above-knee amputees.

The Lic Femurett adjustable training prosthesis was evaluated on 51 above-knee amputees attending the Oxford Disablement Services Centre. In the elderly it proved superior to the Pneumatic Post-Amputation Mobility Aid (P.P.A.M.-Aid) in the assessment of their ability to use a prosthesis, and is useful for walking training once the stump is fully healed; it does not replace the P.P.A.M-Aid at the early post-operative stage.

Adult↗

PubMed1989

Synapses of the inner plexiform layer of the area centralis of kitten retina during postnatal development: a quantitative study.

The frequency of occurrence of conventional synapses in the inner plexiform layer of the area centralis of the kitten retina remained invariant with postnatal age while that of bipolar cell ribbon synapses increased significantly. A significant increase also occurred in the ratio of bipolar cell ribbons to conventional synapses. The counts were made from large montages of electron micrographs in 17 kittens of ages ranging from newborn to 200 days and also in 3 adults. It was confirmed that the observed results were not attributable to an age-related change in the size or orientation of the profiles during postnatal development. The distribution of conventional synapses showed a peak in the middle stratum of the inner plexiform layer which remained invariant with development. By contrast, the distribution of bipolar cell ribbons changed during development, with new ribbons being added to the inner part of the inner plexiform layer.

Animals↗

PubMed1988

The effects of physostigmine sulphate eyedrops on human visual function.

Instillation of 0.25% physostigmine sulphate eyedrops in twelve subjects caused a sustained miosis, a transient reduction in near-point and a transient increase in the amplitude of accommodation. The latter had a peak at 30 min and had recovered by 90 min, though its amplitude varied widely between subjects. Contrast sensitivity to stationary grating patterns of 3-30 cycles/deg and phase-reversed grating patterns of 0.5-3 cycles/deg was reduced transiently with a time course similar to that of the increase in accommodation. The peak reduction in contrast sensitivity was correlated significantly with the peak amplitude of accommodation. Contrast sensitivity to laser interference fringes, observed in Maxwellian view where the effects of defocus are bypassed, was also reduced, indicating that physostigmine also had a direct deleterious action on the visual system.

Accommodation, Ocular↗

PubMed1988

An evaluation of the effectiveness of intramuscular atropine or homatropine eyedrops in preventing the effects of physostigmine eyedrops on human vision.

An intramuscular injection of 2 mg atropine sulphate was given at either 8 or 120 min prior to instillation of 0.25% physostigmine sulphate eyedrops. In this way, the maximum accommodative change and the concomitant reduction in contrast sensitivity caused by physostigmine coincided with, respectively, the peak plasma atropine concentration or the fully developed mydriasis and reduction of near-point accommodation caused by atropine. Atropine at both times did not affect the miosis, the reduction in near-point, the increase in accommodation or the reduction in contrast sensitivity caused by physostigmine. Contrast sensitivity to a phase-reversed grating pattern was actually diminished by atropine, though this was not statistically significant. By contrast, 2% homatropine hydrobromide eyedrops did effectively antagonize physostigmine's actions. This indicates that the rate of delivery of atropine from the intramuscular injection was insufficient to compete against the ocular effects of physostigmine.

Accommodation, Ocular↗

PubMed1988

The effects of ingestion of 60 mg pyridostigmine bromide on contrast sensitivity in man.

The effects on vision of ingestion of the anticholinesterase pyridostigmine bromide (60 mg), assessed from pharmacokinetic data to provide at least 20% inhibition of blood cholinesterase over the 1 1/2-4 1/2 h experimental period, was compared with 60 mg lactose in a double-blind crossover protocol. Contrast sensitivity to stationary oscilloscope-generated gratings of 3-40 c/deg showed a small but significant increase of 7% which was consistent with a small reduction in pupil diameter, surmised to cause a small improvement in optical quality. This reduction in pupil diameter was, however, overshadowed by a larger though still non-significant reduction on the second visit to the laboratory compared with the first. Contrast sensitivities to laser interference fringes observed in the Maxwellian view, by which the effects of the optical media are essentially bypassed, thus providing an entirely neural assessment, were unchanged after pyridostigmine. It is concluded that pyridostigmine may be given as a prophylactic in anticipation of exposure to an organophosphorus anticholinesterase without a deleterious effect on stationary visual function.

Adult↗

PubMed1988

Amputee walking training: a preliminary study of biomechanical measurements of stance and balance.

Biomechanical parameters of stance and balance were recorded in ten unilateral lower limb amputees at the beginning and end of walking training. Measurements were carried out using a Double Video Forceplate (DVF), a machine developed at University College, London, Bioengineering Centre, Roehampton. During free standing on the DVF there was a mean increase in weight-bearing under the prosthetic foot from 32% body weight (1st session) to 41% body weight (final session), p less than 0.01. Maximum weight-bearing during leaning as far as possible onto the prosthesis increased from a mean of 54% body weight to 63% body weight, p less than 0.01. These simple measurements of weight distribution between the feet can be of value during walking training to monitor progress and can accurately record improvement for research purposes.

Aged↗

PubMed1987

Constraints on the performance of minor surgery by family physicians: study of a 'mock' skin biopsy procedure.

Despite the availability of a procedure room equipped for the performance of common surgery procedures, physicians in a family medicine training programme have reported that minor surgery training objectives are not being accomplished. To examine this issue, the frequency of minor surgery procedures was audited among 357 randomly selected medical records. The frequency of documented sigmoidoscopy in this group of active patients over the age of 50 years was 4.8%. A similar low frequency for the performance of skin biopsy was also observed. All 15 senior residents participated in an attitude survey and a timed exercise in which they sought to find the necessary items for performance of a skin biopsy. In a questionnaire the group agreed that sigmoidoscopy and skin biopsies were procedures appropriate for their family practice goals. In their offices, these residents required over nine minutes to partially locate equipment chosen for skin biopsy. The attitude survey revealed few constraints other than insufficient time to perform indicated elective procedures. Further study of procedure room utilization and family physicians' office surgery skills is recommended.

Attitude of Health Personnel↗

PubMed1987

The effects of a single intramuscular injection of atropine sulphate on visual performance in man.

The effects of a single intramuscular injection of 2 mg atropine sulphate on visual function were studied in volunteer subjects. The well-known effects of increased heart rate, dryness of the mouth, increased pupil diameter and reduced accommodative range were confirmed. Visual acuity, stereoacuity, red-green colour balance and reaction time to a visual stimulus were unaffected by atropine, while extraocular muscle balance (horizontal heterophoria and cyclophoria) underwent a transient change. There was no significant change in contrast sensitivity measurements to stationary sinusoidal grating patterns of spatial frequencies 1-30 c/deg; however contrast sensitivity to moving grating patterns of spatial frequencies 1-5 c/deg showed a sustained reduction which was still present at 6 h post-injection. It is concluded that atropine adversely affects movement detection but not stationary visual function.

Atropine↗

PubMed1987

Leg-length inequality in children treated by Syme's amputation.

We have reviewed the results of amputation through the ankle in the management of 37 children with congenital leg-length discrepancy, followed up for a mean of 7.6 years after operation. In general good function was achieved and 18 patients considered their activities to be unrestricted. The main factor affecting the functional result was the underlying condition for which operation had been performed. Although heel pad migration, scar rotation and os calcis remnants were seen, these could be accommodated by the prosthesis. Syme's amputation is tolerated well in the younger child and, in patients with a predicted leg-length discrepancy of over 15 cm associated with an abnormal foot, we recommend the operation as a primary procedure between the ages of 18 months and two years.

Activities of Daily Living↗

PubMed1987

Foot loading characteristics of amputees and normal subjects.

The foot loading characteristics of 100 consecutively attending amputees wearing their definitive prostheses were studied during their routine visits to the Artificial Limb and Appliance Centre. Results were compared with observations on 100 age and sex matched controls who were free from any locomotor disability. The parameters measured were the percentage of body weight borne on each foot, the positions of the centres of pressure under each foot and the position of the overall centre of foot pressure. The results demonstrate the range of variability of these parameters in normal subjects of different ages and provide preliminary indications of the patterns associated with different types of prostheses and different levels of amputation. The information was collected using the Double Video Forceplate (DVF) a tool developed for the rapid assessment of stance, at University College London Bioengineering Centre. It is proposed that the DVF may be useful in assisting prosthetic alignment, in clinical teaching of prosthetists, physiotherapists and doctors and in monitoring of patients with lower limb amputation.

Amputees↗

PubMed1987

A quantitative investigation into the effects of pupil diameter and defocus on contrast sensitivity for an extended range of spatial frequencies in natural and homatropinized eyes.

Contrast sensitivity was measured in 12 subjects for different spatial frequencies of sinusoidal grating patterns, generated by oscilloscope, for pupil diameters 2-8 mm and for defocus of +1-4 D, following homatropine eyedrops. Changes in pupil diameter, without correction for the change in retinal illumination, had no significant effect on contrast sensitivity, except at 0.5 and 1 c deg-1 when a significant reduction occurred with the 2 mm pupil. Defocus caused a large reduction in contrast sensitivity at spatial frequencies higher than the peak of the contrast sensitivity function (3 c deg-1) and a smaller reduction below the peak. In both individual and group results, there was no significant effect of defocus in causing a disproportionately greater reduction in contrast sensitivity at higher spatial frequencies nor were the zero mimina predicted by optical theory observed. The results were confirmed in eight subjects viewing with the natural eye, though the reduction in contrast sensitivity caused by +1 D defocus was not significant: this was attributed to the relaxation of accommodation in response to defocus. To predict the performance of the visual system, multiple regression equations were derived to incorporate terms for pupil diameter, defocus and spatial frequency. These equations reflected the lack of effect of pupil diameter, while defocus caused a 51% loss in contrast sensitivity per dioptre at higher spatial frequencies (3-38 c deg-1) and a 19% reduction at low spatial frequencies.

Accommodation, Ocular↗

PubMed1986

Changing pattern of lower limb amputation for vascular disease.

In 1980 a review of lower limb amputation over a 3.5 year period between 1974 and 1978 was reported from our centre. More recently 193 amputations were performed for peripheral vascular disease over a similar 3.5 year period, representing an increase of 33 per cent in the amputation rate during the last 6 years. This cannot be explained by the increasing age of the population alone. Fewer below-knee amputations (BKA) (33.0 per cent) and more Gritti-Strokes amputations (GSA) (32.0 per cent) were performed and the overall incidence of re-amputation for stump breakdown was 13.5 per cent. Twenty-eight per cent of below-knee amputation stumps required re-amputation at higher levels, but when successful were associated with a 75 per cent incidence of rehabilitation with an artificial limb. Eight per cent of GSA stumps required re-amputation and were associated with a twenty-eight per cent incidence of successful rehabilitation. Thirty-seven per cent of patients had undergone reconstructive vascular surgery before amputation. Of the 26 patients requiring re-amputation 58 per cent had undergone arterial reconstruction in an attempt to salvage the limb (chi 2 = 5.65, P less than 0.02) and in 26.9 per cent of cases this was performed within the week before amputation. We feel that injudicious attempts at arterial reconstruction, when amputation appears inevitable, may adversely affect the subsequent level of amputation and jeopardize rehabilitation.

Age Factors↗

PubMed1986

An assessment of decision-making as a possible factor in the age-related loss of contrast sensitivity.

The possibility that changes in decision-making may contribute to the age-related decline in contrast sensitivity has been investigated in nineteen young subjects (ages 21-38 years) and twenty-seven old subjects (ages 55-92 years). A signal detection paradigm was employed in which the detection of stationary sinusoidal grating patterns was measured at 3 and 15 cycles deg-1 for a range of contrasts which were psychophysically equivalent for each subject. A decline in contrast sensitivity with age at the spatial frequencies studied was confirmed for contrast thresholds obtained both by the ascending method and from the 50% hit rate for detection of the grating pattern. The criterion adopted for decision-making, expressed as both beta and percentage bias, did not change significantly between young and old subjects at 15 cycles deg-1. At 3 cycles deg-1, criterion beta did not change significantly at X0.8, X1.0, or X1.2 contrast threshold, but at contrast giving 50% hit rate there was a significant increase with age. The percentage bias increased significantly at contrast threshold but not at 50% hit rate. It is inferred from the results that the loss of contrast sensitivity was not accountable in terms of the adoption of a more conservative criterion by older subjects. Hence visual loss in ageing is attributed to changes within the visual pathway rather than within higher decision-making centres.

Adult↗

PubMed1985

Assessment of the optical contributions to the age-related deterioration in vision.

Contrast sensitivities were measured in human observers of different ages in response to sinusoidal grating patterns generated by laser interferometer and cathode ray tube (c.r.t.). The former method bypasses the effects of the optical media to assess directly the contrast sensitivity of the retina/visual system, while the over-all assessment including optical media is made to the c.r.t. display. The ratio of the two sets of values gives the contrast ratio of the optical media. The latter assessment does not include the effects of wide-angle light scattering which were measured by comparing the responses of eyes with a Perspex lens implant or without any lens at all (i.e. without the major source of scattering) with natural eyes. With increasing age, c.r.t. contrast sensitivities remained steady until the sixth decade when they declined while laser interference fringe contrast sensitivities declined continuously, apart from some abnormally low results for teenage observers. In contrast, the optical contrast did not vary systematically with age nor did its rate of change with spatial frequency vary. The latter was always less than the rate for laser interference fringe contrast sensitivities indicating that the retina/visual system always sets the limit to visual resolution. Wide-angle light scattering was not found to contribute significantly to the changes in ageing nor did reduced retinal illumination, as reproduced by reduced pupil diameter or viewing through a neutral density filter. We therefore conclude that the age-related deterioration is primarily caused by changes within the central nervous system rather than the optical media, the transmission quality of which remains unaffected.

Adult↗

PubMed1984

Binocular cues in the perception of distance of a point source of light.

The ability to make egocentric distance estimates of a single point source of light, seen in darkness and without the cues of changing size and luminance, was investigated in sixteen observers. The attenuation required to maintain constant luminance, when the target was viewed from different distances, was shown to follow the inverse square law providing the angle subtended by the light was less than 20 s arc. Distance changes were also simulated by means of a split mirror which produced vergence cues, or by test lenses to provide accommodation cues. Over the range 0.5 to 9.2 m distance estimates were surprisingly accurate, although there was some overestimation of near and underestimation of far distances. Most observers made good judgements when only convergence cues were varied, whereas no observers made consistently good judgements when only accommodation cues were varied. The difficulties are discussed in terms of the accommodation-convergence link. When distance was simulated by changing convergence and accommodation cues, estimates were not as good as when real distance was changed. Since good estimates were made with brief target exposures, these judgements were not based on subsequent convergence or accommodation changes. It is suggested that the metric or reference against which the apparently absolute judgements were made was the efferent demand signal associated with a 'resting' position of convergence in darkness.

Accommodation, Ocular↗