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Biomedical subjects

B Sethi

Publications and source records attributed to B Sethi.

At least 19 recordsLinked to original sources
PubMed2005

Effect of opiates on growth hormone secretion in acromegaly.

Morphine at doses of 5 mg and 10 mg does not stimulate growth hormone (GH) secretion in normal subjects, and its effect on GH secretion in acromegaly is not widely documented. We investigated the effect of 15 mg intravenous morphine on growth hormone in patients with active acromegaly compared to normal subjects (7 acromegalics and 5 controls). Their mean (+/- SEM) age was 30.5 +/- 7.6 years and 29.5 +/- 0.5 years, respectively. Basal and peak response of growth hormone after morphine was measured with simultaneous assay of cortisol to exclude the effect of stress. Mean (+/- SEM) basal growth hormone was 103.16 +/- 28.04 ng/ml in acromegalics compared to 4.51 +/- 1.43 ng/ml in controls. Morphine caused an elevation of growth hormone in both acromegalics and normal subjects (p < 0.05). However, the Delta (peak minus basal) response of growth hormone was comparable between the two groups. A concurrent fall in cortisol was noted after morphine in both the groups, excluding the effect of stress on growth hormone. We conclude that higher doses (15 mg) of morphine are required to stimulate GH secretion in normal subjects, and that opioids exert a positive modulating effect on growth hormone secretion in patients with active acromegaly suggesting partial autonomy of the pituitary tumor.

Acromegaly↗
PubMed1990

Prism adaptation and viewing distance.

Previous studies have shown that subjects with normal binocular vision adapt to prism-induced phorias. However, there are conflicting reports as to the amount of adaptation shown to horizontal prisms. Some investigations found a greater amount of adaptation to base out prisms compared with base in, whilst others found the reverse and one study found no adaptation to base out prism at all. This study investigated the adaptation response to horizontal prisms at distance and near in a larger number of subjects (n = 40). The results confirmed our previous findings and showed that at distance the adaptation responses are asymmetrical, there being a significantly greater amount of adaptation to base out prism compared with base in, whilst at near the responses are virtually symmetrical. Possible reasons for these findings are discussed.

Adaptation, Ocular↗
PubMed1989

Adaptation ability of subjects with different refractive errors.

In previous studies we have shown that subjects with normal binocular vision adapt to prism-induced heterophorias. In this study we have continued the work by investigating the adaptation ability of subjects with different refractive errors to horizontal prisms. The results showed that emmetropes, late-onset myopes (LOM's), and early-onset myopes (EOM's) can adapt to prism-induced phorias at distance and at near. The early-onset myopes demonstrated the greatest amount of adaptation after 3.5 min of binocular viewing in all cases. However, the differences found between the refractive groups in the amount of adaptation after 3.5 min of binocular viewing are not statistically significant.

Adaptation, Ocular↗
PubMed1987

Vergence adaptive changes with varying magnitudes of prism-induced disparities and fusional amplitudes.

Vergence adaptation response monitored with various prism disparities demonstrated that the rates of adaptation decreased as the prismatic effect was increased. However, the amount adapted increased with the increase in the value of the prism until this value fell outside the fusional amplitude; the amount adapted then decreased. However, a large disparity can be adapted to with ease if the prismatic effect is increased gradually in small steps. The clinical implications of these results are discussed.

Adaptation, Ocular↗
PubMed1986

Vergence adaptation: a review.

The present review aims to discuss the current researches on the ability of the vergence system to adjust to new information. A concomitant or non-concomitant binocular retinal disparity caused by a prism or an anisometropic prescription can be adapted to such that the induced phoria of fixation disparity reduces back to the original value. The features and mechanisms of this normal adaptation and also the response in subjects with abnormal binocular vision are discussed. The less extensive work on the adaptive ability of the accommodative vergence system is also reviewed.

Accommodation, Ocular↗
PubMed1986

Heterophoria: a vergence adaptive position.

Previous experiments have shown that as the adaptive change becomes more complete with prolonged wear of a prism, the adaptive decay during monocular occlusion (MO) becomes slower; at the same time, adaptation to a further prism disparity becomes faster. If phoria is an adapted position of the oculomotor system then, as with prism adaptation, it should demonstrate an adaptive decay during MO. The rate of this decay should be inversely related to the rate of adaptation to a prism. In the first part of the paper, changes in the horizontal and vertical phorias were demonstrated at distance and near during 4 hr of MO. In the second part, adaptation to various prism disparities (horizontal and vertical) was monitored. The rates of adaptation were found to be inversely related to the rates of phoria decay during MO. The phoria position is, therefore, an adapted position of the vergence system.

Accommodation, Ocular↗
PubMed1986

Effects of prolonged forced vergence upon the adaptation system.

In previous studies the ability of the oculomotor system to adapt to prism-induced heterophoria has been shown. The 'phoria that occurs immediately after a prism has been placed before one eye gradually reduces and returns to its original baseline value as the subject is allowed binocular experience while wearing the prism. Little work has been carried out to determine when the adaptation is complete. In this study we report on the results of two experiments designed to determine when adaptation is complete. In the first, the rate of decay of adaptation, i.e. loss of slow fusional vergence, is measured after varying periods of forced vergence. In the second experiment the rate of adaptation to an additional disparity is measured; this should be the same as that before the induced effect if adaptation is complete. The results of this study indicate that although adaptation may appear complete by the criterion that the 'phoria has returned to its baseline value, the adaptation is unlikely to be truly complete for a much longer period of time has passed.

Adaptation, Ocular↗
PubMed1985

Vergence-adaptive change with a prism-induced noncomitant disparity.

Oculomotor adaptation to a magnified motor field in one eye can occur as a result of the vergence system responding either to (1) the magnification of the field, or (2) via small adaptive fields. This was investigated by monitoring adaptation with the whole oculomotor field magnified in one experiment, and just the central motor field magnified in another experiment. It was shown that adaptation in the periphery occurred at a much slower rate when it was occluded. It is concluded that adaptation in the periphery occurs via adaptive spread from central positions and not via a direct response to the magnification of the oculomotor field.

Adaptation, Physiological↗
PubMed1984

Adaptive changes with prolonged effect of comitant and incomitant vergence disparities.

When comitant and incomitant vergence disparities are induced for prolonged periods of time, the adaptive state becomes more stable. When the change is complete, the adaptive ability of the oculomotor system to a further disparity should be the same as that before any induced effect. Comitant change was investigated in five subjects who wore a 2 delta base-up Fresnel prism for prolonged periods of time (1 to 3 days). Adaptation was periodically monitored with a further 2 delta base-up prism. In three subjects the rate of adaptation to the additional prism approached that which occurred before the experiment. In two subjects, both of whom suffered asthenopic symptoms with the initial disparity, adaptation to the additional prism remained slow and incomplete. Incomitant change was investigated in two subjects who wore a -3.00 contact lens-spectacle lens (CL-SL) system for 2 to 3 days. Adaptation was monitored with a further -1.50 CL-SL system at the start and the end of the prolonged wear. Both these subjects had a much faster rate of adaptation at the end of the prolonged period than they had at the beginning.

Adaptation, Ocular↗