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Biomedical subjects

B Gilmartin

Publications and source records attributed to B Gilmartin.

At least 73 records · Page 4Linked to original sources
PubMed1988

Disparity-induced accommodation in late-onset myopia.

The effect of disparity-vergence on the accommodation response (AR) was measured in 10 late-onset myopes (LOMs) and 10 emmetropic subjects during the course of a 10 minute near-vision task (working distance 33 cm). Disparity was induced by the introduction of 3 and 6 delta base-out prisms placed before the right eye, and the resulting AR for the left eye was measured at 1 min intervals using an objective infra-red optometer. LOMs showed a significant increase in AR with increasing disparity whereas emmetropes showed no significant difference in AR for all disparity conditions. The implications of these findings are discussed with reference to the aetiology of late-onset myopia.

Accommodation, Ocular↗
PubMed1988

Factors affecting the normal perimetric profile derived by automated static threshold LED perimetry. II. Accommodative microfluctuations.

The relationship between accommodative fluctuations and perimetric sensitivity was investigated in a group of 10 clinically normal emmetropic subjects using the Dicon AP3000 computer-assisted perimeter at a bowl luminance of 10 asb. Accommodative microfluctuations were attenuated with the antimuscarinic drug cyclopentolate HCl 1% and the concomitant mydriasis was matched on a separate trial using the sympathomimetic phenylephrine HCl 10%. Saline 0.9% was used as the control. Accommodative microfluctuations were found to play a minor role in determining the magnitude of sensitivity out to an eccentricity of 5 degrees; between 5 degrees and 27.5 degrees, the effect of microfluctuations was masked by the mydriasis produced by the drugs used in the study. The range of sensitivity values at a given location were reduced when accommodative fluctuations were minimized.

Accommodation, Ocular↗
PubMed1987

Tonic accommodation, cognitive demand, and ciliary muscle innervation.

An infrared optometer was used to investigate the relation between cognitive induced shifts in tonic accommodation (TA) and ciliary muscle innervation. Twenty emmetropic men volunteers took part in a double-masked protocol which involved high (a reverse counting task) and low levels of mental load and blocking of sympathetic innervation of the ciliary muscle with the nonselective beta receptor antagonist timolol maleate (0.5%). The high level of cognitive demand induced shifts in TA of up to +1 D. There was no clear reason why large differences in intersubject susceptibility to these shifts occurred. The effect of beta-antagonism on these shifts was insignificant for subjects having initial TA values less than 1.2 D. However, sympathetic antagonism induced significant increases in cognitive shifts for the remaining subjects. The inference is that cognitive induced shifts in TA are predominantly parasympathetic mediated although a sympathetic attenuation may occur at higher levels of TA.

Accommodation, Ocular↗
PubMed1987

Aspects of tonic accommodation in emmetropia and late-onset myopia.

An objective infrared optometer was used to investigate the influence of cognitive demand on tonic accommodation (TA) for two groups of young emmetropes (N = 15) and late-onset myopes (N = 15). TA was measured under a passive condition and while subjects carried out a reverse counting task. The TA of myopes under the passive condition (mean = 0.81 D, SD = 0.46 D) was shown to have lower values than the TA of emmetropes (mean = 1.14 D, SD = 0.46 D). For the myopic group the counting task induced a positive shift in TA (mean = +0.35 D, SD = 0.31 D) that was significantly higher than that for the emmetropic group (mean = +0.07 D, SD = 0.27 D). The implications for theories of refractive error development are discussed.

Accommodation, Ocular↗
PubMed1987

Synkinesis of accommodation and vergence in late-onset myopia.

The accommodative response (AR) to disparity-vergence and blur stimuli was determined for 45 subjects; 15 emmetropes, 15 late-onset myopes (LOM's), and 15 early-onset myopes (EOM's). The accommodative response was measured at approximately 1-s intervals for 50 s using an objective infrared optometer. Disparity-driven accommodation was induced by a 4 delta base-out prism at accommodative stimulus levels of 2.50 and 3.25 D. LOM's show significantly higher levels of disparity-induced accommodation when compared with the other two refractive groups. Blur-induced accommodation was produced by increasing the accommodative stimulus from 2.50 to 3.25 D with no concomitant change in vergence stimulus. EOM's exhibit less blur-induced accommodation compared with LOM's and emmetropes. These results are discussed with reference to differences in accommodation-vergence synkinesis between LOM's and EOM's, and in relation to the etiology of late-onset myopia.

Accommodation, Ocular↗
PubMed1987

Oculomotor consequences of beta-adrenoceptor antagonism during sustained near vision.

The effect of a topical non-selective beta-adrenergic antagonist, timolol maleate (0.5%) on the response accommodative convergence/accommodation (AC/A) ratio was monitored during a 16 min near-vision task. A double-blind protocol was adopted between timolol and a saline control for 17 emmetropic subjects. Timolol produced a significant reduction in AC/A during the first 4 min of the task with respect to saline. This reduction was mediated via accommodative convergence and it is proposed that this demonstrates direct involvement of sympathetic innervation to the ciliary muscle during the initial stages of a near-vision task.

Accommodation, Ocular↗
PubMed1987

Beta-adrenergic receptor antagonism in myopia.

A previous study has demonstrated that timolol maleate (0.5%), a non-selective beta-adrenergic antagonist, produces in emmetropes a significant reduction in accommodative convergence (AC) during the initial four minutes of a near-vision task. The present study has examined the effect of timolol on AC for three refractive groups (each comprising N = 20): emmetropes, early-onset myopes (EOMs), i.e. myopia onset prior to 15 years of age and late-onset myopes (LOMs), i.e. myopia onset after 15 years. A double-blind protocol was adopted between timolol and a saline control. AC was derived from accommodation stimuli of 3.3, 4.1 and 4.8 D with changes in heterophoria being assessed using a Maddox rod and tangent scale. The relationship between the ocular hypotensive effect of timolol and anterior corneal curvature was also investigated using a Goldmann applanation tonometer and a two-position keratometer (Haag-Streit). Timolol produced a significant reduction in AC in emmetropes but did not induce significant changes in AC in LOMs or EOMs. The timolol-induced reduction in IOP did not result in any changes in anterior corneal curvature.

Accommodation, Ocular↗
PubMed1987

The Marton Lecture: Ocular manifestations of systemic medication.

The probability of ocular adverse reactions to systemic medication is low but when a reaction does occur it is often associated with one or more special factors relating to the condition being treated, to the patient, and to the nature of the drug itself. Nevertheless the role of the optometrist in the monitoring, detection and reporting of adverse reactions is important and is recognized by the College reporting scheme. A selection of the type of reactions that may be encountered in general optometric practice is reviewed. The reactions range from the relatively innocuous anticholinergic effects of the benzodiazepine tranquillizers to the more serious corneal, lens and retinal changes that may be associated with the corticosteroids, phenothiazines and chloroquine.

Age Factors↗
PubMed1987

Effect of a near-vision task on the response AC/A of a myopic population.

The effect of a 14 minute near-vision task on the response accommodative convergence/accommodation (AC/A) ratio was investigated for three refractive groups (each comprising N = 17)--emmetropes, early-onset myopes (EOM), i.e. myopia onset prior to 15 years of age, and late-onset myopes (LOM), i.e. onset 15 years or later. AC/A ratios were derived from accommodative stimuli of 3.0, 3.9 and 4.6 D. Accommodation was measured using an objective infra-red autorefractor which allowed unrestricted viewing through a semi-silvered mirror and this permitted concomitant vergence changes to be assessed using a Maddox rod and tangent scale. EOMs exhibit a significantly higher response AC/A ratio than the two other refractive groups. The implications of these modifications in response AC/A are discussed with reference to current models of accommodation-vergence interaction.

Accommodation, Ocular↗
PubMed1986

A review of the role of sympathetic innervation of the ciliary muscle in ocular accommodation.

Although it is well established that autonomic control of ocular accommodation is predominantly parasympathetic, many investigators have, over the last 150 years, proposed that a supplementary sympathetic innervation should be considered. Particular attention is directed in this review to previous literature providing anatomical, physiological and pharmacological evidence for dual innervation of the ciliary muscle. Clinical and psychological evidence is shown to be equivocal. A review of recent laser optometry studies of tonic ("dark-focus") resting positions of accommodation indicates that the inhibitory nature of sympathetic innervation suggested by the majority of previous studies can be further defined with respect to specific adrenergic receptors. The implications of dual innervation relating to ocular accommodation during sustained near-vision tasks is discussed.

Accommodation, Ocular↗
PubMed1986

Objective and subjective measurement of tonic accommodation.

Measurements of tonic accommodation (TA) were made on 25 subjects using He-Ne laser optometry (HNL), infra-red optometry (IR) and near retinoscopy (NR) under darkroom conditions. All three techniques were shown to produce comparable mean estimates of TA (HNL: 1.10 D; IR: 1.15 D; NR: 1.07 D). Significant correlations were found between HNL and IR (r = 0.88, p less than 0.001) and between HNL and NR (r = 0.81. p less than 0.001). Control studies under cycloplegia indicate that the estimates are not seriously affected by fluctuations in accommodative state. These findings indicate that ophthalmic practitioners can gain access to refractive data that aids the clinical management of the "anomalous myopias" and asthenopia associated with VDU work.

Accommodation, Ocular↗
PubMed1985

The magnitude of longitudinal chromatic aberration of the human eye between 458 and 633 nm.

The longitudinal chromatic aberration (LCA) of the human eye was determined between wavelengths 458 and 633 nm for ten observers by incorporating Argon and Helium-Neon Lasers into a Badal optometer system such that tonic (or "dark focus") resting positions of accommodation could be measured under darkroom conditions. A mean chromatic range of 1.87 D was found between 488 and 633 nm. The range increased slightly to 1.91 D when the experiment was repeated under cycloplegia on a subset of three subjects. Additional wavelengths (458 and 476 nm) for a further subset (four subjects) increased the range to 2.65 D. This magnitude of LCA would support recent predictions based on Abbe and Pulfrich refractometry analyses of the dispersion of the human crystalline lens and ocular media.

Accommodation, Ocular↗
PubMed1985

Visual performance with soft hydrophilic contact lenses.

An instability of the visual correction is sometimes associated with soft hydrophilic contact lenses. However, this problem does not seem to have detracted from the commercial success of this form of refractive aid. To facilitate the quantification of visual performance during soft lens wear, a televised test system was developed and has been fully described elsewhere. Results are now presented of a clinical study using this television (TV) system. Visual performance scores, in conjunction with response latency and blink activity data, were obtained from the eyes of 27 experimentally naïve subjects during the first month of adaptation to soft contact lens wear. The results suggest that the soft contact lens wearer has recourse to a strategy whereby he can optimize his level of visual performance when necessary.

Adult↗
PubMed1985

The relationship between tonic accommodation and ciliary muscle innervation.

Previous studies have used Badal laser optometry to demonstrate significant variance in the distribution of tonic (or "dark-focus") resting positions of accommodation (TA) for groups of observers. This study investigates whether individual differences in TA are due to individual differences in autonomic tone of the ciliary muscle by comparing separately the effects of a muscarinic receptor antagonist (Tropicamide 0.5%) and a beta receptor agonist (Isoprenaline 3%) on the distribution of TA. Ten subjects were used for each study with mean ages of 23.2 and 23.0 yr, respectively. The distribution of TA within each subject group was equivalent to the large sample distributions published in previous literature. Darkroom measurements of TA and pupil diameter were determined with a Badal laser optometer and infrared photography. Distance correction and amplitude of accommodation were determined by standard optometric techniques. Isoprenaline produced a significant hyperopic shift in TA of 0.47 D over 22 min but this was not accompanied by a significant change in standard deviation of the TA distribution. This finding was in accord with the authors' previously reported investigation using the beta receptor antagonist Timolol Maleate. Tropicamide also produced a significant hyperopic shift in TA of 1.24 D over 24 min, and this was accompanied by a significant change in standard deviation of the distribution from 0.87 to 0.17. The results indicate that the parasympathetic system plays a significant role in determining the TA position and that the variations in TA between individuals is a consequence of parasympathetic rather than sympathetic ciliary muscle tone.

Accommodation, Ocular↗
PubMed1985

The relationship between tonic vergence and oculomotor stress induced by ethanol.

Previous investigations have demonstrated an ethanol-induced increase in distance esophoria and an increase in near exophoria, together with a decrease in negative fusional ability, the AC/A ratio and near point of convergence. The present study (N = 10) was designed to test the hypothesis that these effects are due to a biasing of vergence towards its tonic resting state when under conditions of oculomotor stress. Measurements of the parameters before and 1 hr after imbibition of a moderate dose of ethanol supported the previous findings. Darkroom measures of tonic vergence (vernier alignment) and tonic accommodation (laser optometry) were unaffected by ethanol. The study indicates that the changes in oculomotor function induced by the central inhibitory action of ethanol represent a shift towards the tonic vergence position.

Accommodation, Ocular↗