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| Research article summary (published 30 Aug 2002): |
Effect of beta-adrenoceptor antagonists on autonomic control of ciliary smooth muscle.
Full Abstract
PURPOSE:
Pharmacological intervention with peripheral sympathetic transmission at ciliary smooth muscle neuro-receptor junctions has been used against a background of controlled parasympathetic activity to investigate the characteristics of autonomic control of ocular accommodation.
METHODS:
A continuously recording infra-red optometer was used to measure accommodation on a group of five visually normal emmetropic subjects under open- and closed-loop conditions. A double-blind protocol between saline, timolol and betaxolol was used to differentiate between the localised action on ciliary smooth muscle and effects induced by changes in stimulus conditions. Data were collected before and 45 min following the instillation of saline, timolol or betaxolol. Open-loop post-task decay was investigated following 3 min sustained near fixation of a stimulus placed 3 D above the subject's pre-task tonic accommodation level. Closed-loop dynamic responses were recorded for each treatment condition while subjects viewed sinusoidally (0.05-0.6 Hz) or stepwise vergence-modulated targets over a 2 D range (2-4 D).
RESULTS:
Open-loop data demonstrate a rapid post-task regression to pre-task tonic accommodation levels for saline and betaxolol control conditions. A slow positive post-task shift was induced by timolol indicating that sympathetic inhibition contributes to accommodative adaptation during sustained near vision. Closed-loop accommodation responses to temporally modulated sinusoidal stimuli showed characteristic features for both saline and betaxolol control conditions. Timolol induced a reduced gain for low- and mid-temporal frequencies (< 0.3 Hz) but did not affect the response at higher temporal frequencies. Response times to stepwise stimuli increased following the instillation of timolol for the near-to-far fixation condition compared with the controls and was related to the period of sustained prior fixation.
CONCLUSIONS:
Modulation of accommodation under open- and closed-loop conditions by a non-selective beta-blocker is consistent with the temporal and inhibitory features of sympathetic innervation to ciliary smooth muscle. Although parasympathetic innervation predominates there is evidence to support a role for sympathetic innervation in the control of ocular accommodation.
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Author information
Author/s: Winn, Barry (B); Culhane, Helena M (HM); Gilmartin, Bernard (B); Strang, Niall C (NC);
Affiliation: Department of Optometry, School of Life Sciences, University of Bradford, UK. b.winn(-atsign-)bradford.ac.uk
Journal and publication information
Publication Type: Clinical Trial; Journal Article; Randomized Controlled Trial
Journal: Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians (Optometrists) (Ophthalmic Physiol Opt), published in England. (Language: eng)
Reference: 2002-Sep; vol 22 (issue 5) : pp 359-65
Dates: Created 2002/10/02; Completed 2002/10/17; Revised 2006/11/07;
PMID: 12358303, status: MEDLINE (last retrieval date: 11/6/2008)
Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.
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