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Biomedical subjects

J Atkinson

Publications and source records attributed to J Atkinson.

At least 217 records · Page 12Linked to original sources
PubMed1983

Reaching for rattles: a preliminary study of contrast sensitivity in 7-10 month old infants.

Contrast sensitivity for a 3 cycles deg-1 sinusoidal grating in 7-10 month old infants was tested by presenting gratings and uniform fields on cylinders, with the former providing auditory reinforcement when the infant picked them up. The method shows that a contrast as low as 7.5% can commonly be detected at this age, compared with 1-2% for adults under comparable conditions. However, as the development of hand preferences with the task as an indicator of visual sensitivity, it is concluded that this method is not in its present form suitable for vision testing on a wide scale or in a clinical setting.

Discrimination Learning↗
PubMed1983

Assessment of visual acuity in infancy and early childhood.

The forced-choice preferential looking method (FPL) shows the development of acuity during the first year of life, and is applicable to clinical assessment. A tracking test using a narrow strip of grating yields a more sensitive measure for the later part of this age range, however. The development of acuity is dominated by neural rather than optical or accommodative factors. By age 3 years resolution acuity is very close to adult performance, but at 5 years 'crowding' effects may still impair performance on practical acuity tasks more than for the adult.

Adult↗
PubMed1983

The development of binocular function in infancy.

Binocular function in infancy can be assessed by means of the visual evoked potential (VEP) induced by a dynamic random dot pattern which alternates between a binocularly correlated and an anticorrelated state. A VEP time-locked to the alternation can only be produced by binocular interaction in the cortex. This interaction becomes detectable at around three months of age. Optokinetic nystagmus (OKN) in monocular viewing becomes symmetrical in nasal and temporal directions around the same age. Animal analogues and clinical cases suggest that this may also be an indicator of cortical binocularity. These techniques may be applicable to clinical assessment of binocular function in young infants.

Animals↗
PubMed1983

The use of isotropic photorefraction for vision screening in infants.

Isotropic photorefraction is a technique which makes possible the rapid, economic, large scale screening of infants and young children for refractive errors. The relative size of blur circles reflected from the fundus in 3 flash photographs with different camera settings allows the size and direction of refractive errors to be estimated. The method has been validated against retinoscopic measures on a large group of infants. Findings of a high incidence of astigmatism in the first year are confirmed. Detection of hypermetropia in early infancy by this screening procedure may allow preventive treatment for accommodative strabismus.

Astigmatism↗
PubMed1983

Optics of photorefraction: orthogonal and isotropic methods.

Analysis of the optics of photorefractively computed ray tracing shows that, for short camera-to-subject distances, the function relating image size to defocus of the eye is not symmetrical for errors of focus in front of and behind the camera. This asymmetry is exploited in the new method of isotropic photorefraction, in which the supplementary cylinder lenses of the original orthogonal photorefractors are replaced by defocusing of the camera lens itself. By comparing photographs taken with the camera focused in front of and behind the subject, the sign of the eyes' defocus (myopic or hyperopic relative to the camera) can be determined. The axis of any astigmatism is readily apparent as the direction in which the photorefractive images are elongated. The method is well adapted for the refractive screening of infants and young children.

Astigmatism↗
PubMed1983

The onset of binocular function in human infants.

Visual evoked potentials (VEP) elicited by a dynamic random-dot correlogram were used to assess the development of cortical binocular function in infant subjects. In a group of newborn infants who showed a VEP for a comparable non-binocular stimulus, none showed evidence of binocular function. A further group of infants were tested longitudinally, starting between 35-50 days. The median age for the first evidence of binocular function in this group was 91 days, with individual variation from 54 to at least 105 days.

Aging↗
PubMed1982

Effects of vestibular stimulation in seizure-prone children. An EEG study.

Concern that vestibular stimulation may induce seizures in seizure-prone children has been based on hearsay and unconfirmed clinical impressions of practicing therapists. To clarify this issue, we took electroencephalographic recordings of seizure-prone children before, during, and after specific vestibular stimulation. Ten children with seizure histories, 5, to 15 years of age, were exposed to warm and cold caloric vestibular stimuli. Electroencephalographic activity was recorded before, during, and after each vestibular stimulus; recordings were rated and compared prevestibular and postvestibular stimulation. Electronystagmographic recordings were also taken. Results show that vestibular stimulation does not accentuate the abnormal brain wave pattern in seizure-prone children. Six of 10 subjects had a significant reduction in paroxysmal activity (p less than .02). Possible explanations for clinical reports of vestibular induced seizures are given, with suggestions for precautions when applying vestibular stimulation to seizure-prone children.

Adolescent↗
PubMed1982

Evaluation of a diabetes education programme.

An education programme was evaluated for 140 insulin-dependent diabetics and their family members from 1978 to 1980. Dietary, biochemical and other assessments were made before and 6 months after the programme. As a group, the diabetics were initially in good metabolic control and this was maintained, or improved, over the study period. The programme recommended a diet in which complex carbohydrate constituted at least 45% of energy intake and fat was limited to 30%. The diabetics and their family members significantly increased their consumption of complex carbohydrate and decreased fat intake. On this regimen, diabetics did not gain weight and their relatives lost weight. There were also improvements in knowledge of the disorder and in perceptions of susceptibility to complications and barriers to compliance.

Attitude to Health↗
PubMed1982

'Preferential looking' for monocular and binocular acuity testing of infants.

A method is described for obtaining rapid and reliable estimates of acuity in infants, for both monocular and binocular viewing. The method depends on 'preferential looking', where the infant prefers to look at a striped pattern rather than a blank screen of matched mean luminance. A staircase procedure for testing is followed, with observations being recorded by a 'blind' observer (who does not know on which of the 2 screens the striped pattern is displayed). Monocular acuity estimates have been obtained for a group of infants 3 to 4 months old with normal refractions. Many of these infants show similar acuity values in the 2 eyes, with a few showing reliable differences between the eyes. To check reliability of the method a comparison of 2 independent interleaved staircase estimates of the same eye have been made. In general this check shows highly consistent estimates for a given eye of a given infant. Nearly all infants show slightly higher acuity estimates for binocular viewing than for monocular. The possible reasons for this difference are discussed. The clinical use of such a method is reported for a number of cases. The method has been found to be useful in a variety of clinical conditions where other available tests are not possible on young infants.

Child, Preschool↗
PubMed1982

The role of plasma and renal renin in the rise in blood pressure following unilateral renal artery constriction.

Constriction of the artery to the remaining kidney of control rats uninephrectomized 24 h previously induced a sixfold rise in plasma renin level from 11 +/- 1 to 60 +/- 11 ng AI ml-1 h-1, a 43% decrease of renal cortical renin level, and a 21% rise of mean arterial pressure from 119 +/- 2 to 144 +/- 3 mm Hg. Constriction of the artery to a renin-depleted kidney (with a renin level which was 5% of normal) was not followed by any significant increase in plasma renin level or mean blood pressure. Renin-depleted kidneys were produced by removing the clipped kidney from two-kidney one-clip hypertensive rats, 24 h before the experiment. Such a maneuver induces renin depletion but does not completely normalize blood pressure. When a large dose of frusemide (50 mg/kg i.p.) was injected immediately following removal of the clipped kidney, mean arterial pressure (117 +/- 7 mm Hg) returned to control values 24 h later but again constriction of the remaining renal artery failed to induce a rise in plasma renin level or mean arterial pressure. By 7 days after removal of the clipped kidney, plasma renin level and mean arterial pressure were normal and clipping of the remaining kidney (in spite of the fact that kidney renin level was still low) now produced a wave of renin release and an increase in mean arterial pressure. These results suggest that the initial, rapid increase in mean arterial pressure following unilateral renal artery constriction is dependent on an increase in plasma renin level. Our results from animals with kidneys of varying renin levels suggest the existence of a cortical renin content of about 20% of normal below which the kidney is incapable of responding to renal artery constriction with significant renal release. Complete recovery of the renin (and blood pressure) response to clipping occurred when the renin content had reached about 75% of normal.

Animals↗
PubMed1982

Interaction between the renin-angiotensin and beta adrenergic nervous systems in drinking and pressor responses after renal artery constriction.

Constriction of the remaining renal artery of a uninephrectomized rat produced an increase in plasma renin level, a decrease in renal cortex renin level, an increase in blood pressure and a drinking response. Simultaneous infusion with the angiotensin II antagonist, saralasin, potentiated the rise in plasma renin level and blocked the rise in blood pressure. Drinking was only partially attenuated. Pretreatment with l-propranolol had no effect on the changes in plasma or kidney renin levels, but the increase in blood pressure was potentiated and the drinking response was attenuated. It is concluded that the pressor and drinking responses to renal artery constriction are partially mediated by the beta adrenergic nervous system.

Angiotensin II↗
PubMed1981

Renin release by renin-depleted rats following hypotensive haemorrhage and anesthetics.

1. Renin-depletion, described as a decrease in renal cortex and plasma renin levels, was produced by clipping one renal artery of a rat and leaving the contralateral kidney in place (two kidney one clip hypertension), One month later the clipped kidney was removed and after 24 h recovery such rats were found to be renin depleted: renal cortex and plasma renin levels were 8 and 63% of normal respectively. 2. Such renin depleted rats were incapable of releasing renin (as judged by increase in plasma renin level) in response to severely hypotensive haemorrhage and had very blunted renin release responses to pentobarbital and urethane anesthesia (59 and 17% of normal respectively). 3. Our results confirm the hypothesis that a low renal renin status is associated with low basal and stimulated renin release. We suggest that the renin depleted rat may be a useful model for the study of the role of the renin angiotensin system in phenomena such as blood pressure compensation following hypotensive haemorrhage and drinking induced by beta-adrenoreceptor agonists.

Anesthetics↗
PubMed1981

Contrast sensitivity function of preschool children.

A procedure specifically adapted for children of preschool age has been used to measure contrast sensitivity in emmetropic children aged 3 to 5 years. Mothers of the children acted as adult observers using the same procedure. The results show that the contrast sensitivity function of adults and children is very similar, sensitivity for the children being slightly lower than that for adults at all spatial frequencies. The sensory and cognitive factors involved in these differences are discussed.

Adult↗
PubMed1981

Does the Catford drum give an accurate assessment of acuity?

Adult emmetropes and myopes were tested with the Catford drum and the results compared with subjective (Landolt C) acuity. For he emmetropes the Catford drum was found to overestimate visual acuity by a factor of approximately 4. For myopes, and emmetropes viewing through plus lenses, the discrepancies were much larger. Since the Catford drum not only overestimates acuity but will do so by a factor which varies for different visual disorders, caution is needed in clinical interpretation of results obtained with it.

Adult↗