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Biomedical subjects

M Rosenfield

Publications and source records attributed to M Rosenfield.

At least 55 records · Page 3Linked to original sources
PubMed1990

Effect of target proximity on the open-loop accommodative response.

Proximal stimuli to accommodation were assessed by comparing the open-loop accommodative responses (AR's) to stimuli placed at viewing distances of 5 m (0.2 D) and 0.33 m (3D) in 10 late-onset myopes (LOM's) and 10 emmetropes. The accommodation and vergence loops were opened by subjects viewing targets monocularly through 0.5-mm pinholes. Pre- and post-task levels of tonic accommodation (TA) were used to assess the accommodative adaptation induced by the task. For the 0.2 D condition there was no significant difference between pre-task TA, within-task AR, or post-task TA, indicating that accommodation was open-loop throughout this distal condition. When viewing the 3 D target both refractive groups exhibited significant increases in AR, emmetropes showing higher levels of proximally induced accommodation (PIA) when compared with LOM's. The data indicate that target proximity will influence AR even when both blur and vergence cues have been stabilized.

Accommodation, Ocular↗
PubMed1990

Distance heterophoria and tonic vergence.

It has previously been suggested that the difference between tonic vergence (TV) and distance heterophoria may relate either to proximally induced vergence or accommodative divergence. To identify which of these components was responsible for this difference, the present study compared TV and distance heterophoria in a population of 20 subjects. However, distance heterophoria was now assessed with open-loop accommodation. No significant difference was observed between these two measures. This suggests that the previously observed variations between TV and distance heterophoria (with accommodation closed-loop) were produced by accommodative divergence. However, in a subgroup of 7 subjects, measurements of TV were more convergent (greater than 2 delta) than the distance heterophoria. In these subjects, proximally induced vergence may have accounted for the difference in response.

Accommodation, Ocular↗
PubMed1990

Accommodative responses to naturalistic stimuli.

Steady-state accommodative responses to a wide range of commonly encountered textural and graphic stimuli were investigated in 12 young, visually normal subjects. Details of two experiments are described. In the first experiment, stimuli were varied in terms of size, contrast, spatial frequency, colour and intellectual demand. In the second experiment, only the colour of the targets was systematically altered. In both experiments the stimulus demand was maintained at 3 D, and accommodation was measured subjectively using a Hartinger coincidence optometer. No significant difference in mean accommodative response was observed between the widely differing targets adopted in either experiment. These findings suggest that an overall threshold exists for accommodative stimuli, with supra-threshold targets of low to moderate contrast being capable of initiating and sustaining an appropriate accommodative response.

Accommodation, Ocular↗
PubMed1990

The influence of alpha-adrenergic agents on tonic accommodation.

This study has examined the effect of an alpha-1 adrenergic agonist (phenylephrine HCl, 2.5%) and a non-selective alpha antagonist (thymoxamine HCl, 0.5%) on tonic accommodation (TA). TA was measured at 1 min intervals throughout a 45 min period using an objective infra-red optometer (Canon Autoref R-1). Additionally pupil diameter and the near-point of accommodation (NPA) were monitored in order to assess the efficacy of the instilled drug. A double-blind protocol was adopted between thymoxamine, phenylephrine and a saline control for 7 emmetropic subjects. There was no significant difference between the values of TA obtained under the three pharmacological conditions. However, both adrenergic agents induced changes in pupil diameter and NPA. Furthermore in all conditions TA increased by approximately 0.25D while the subject sat passively in darkness. The data indicates that alpha-adrenergic innervation alters the closed-loop accommodative response independently of TA.

Accommodation, Ocular↗
PubMed1990

Proximal and cognitively-induced accommodation.

The aim of this study was to investigate proximally-induced accommodation (PIA) at two levels of cognitive demand. PIA was assessed by comparing the open-loop accommodative responses to stimuli located at viewing distances of 6 m (0.17 D) and 0.33 m (3 D), respectively. The vergence and accommodation loops were opened by subjects monocularly viewing the targets through a 0.5 mm pin-hole. PIA was measured while subjects either were encouraged to relax and listened to popular music, or performed a relatively demanding mental arithmetic task (counting backwards in sevens). The results indicated that for 4 of the 12 subjects examined, increased cognitive demand produced a marked (greater than +/- 1.00 D) change in the magnitude of PIA. This finding suggests the presence of an interaction between the output of proximally- and cognitively-induced accommodation in these subjects. Such an interaction may hinder attempts to examine individual, non-optical components of accommodation.

Accommodation, Ocular↗
PubMed1990

Proximally induced accommodation and accommodative adaptation.

To determine the effect of proximally induced accommodation (PIA) on accommodative adaptation, this study has examined the posttask shift in tonic accommodation (TA) following 5-min monocular viewing of equivalent-sized targets located at distances of 0.33 and 5 m. The distal target was viewed through a negative lens to equate the dioptric stimuli (3 D). The steady-state accommodative response was measured subjectively in 10 subjects using a Hartinger coincidence optometer. A significant correlation was observed between the degree of adaptation following the two conditions, with the magnitude of adaptation for the distal target being approximately half that for the nearer target. Furthermore, adaptation magnitude was inversely correlated with pretask TA under both conditions. These results indicate that PIA can produce accommodative adaptation. The implications of this finding are discussed with regard to models of the accommodative mechanism.

Accommodation, Ocular↗
PubMed1989

Temporal aspects of accommodative adaptation.

Pre- and post-task measures of dark focus (DF) were used to assess accommodative adaptation induced by brief near-vision tasks in 10 late-onset myopes (LOM's) and 10 emmetropes. The degree of adaptation was examined after tasks of 15, 30, and 45 s duration. Accommodation was measured after the task at 1 s intervals over a 90 s period using an objective infrared optometer. Emmetropic subjects showed a significant increase in DF during the first 10 s of post-task recording, which regressed to the pre-task value within a further 20 to 30 s. No significant difference in post-task accommodative regression was observed after the three task durations. Similar findings were observed for LOM's after the 15 and 30 s tasks. However, after the 45 s task, LOM's exhibited a marked negative shift in DF during the 10 to 50 s post-task period. Instillation of a beta adrenergic antagonist attenuated this negative shift, suggesting that it was mediated via beta adrenergic innervation to the ciliary muscle.

Accommodation, Ocular↗
PubMed1989

Evaluation of clinical techniques to measure tonic accommodation.

Previous studies have advocated the use of a degraded accommodative stimulus to assess the value of tonic accommodation (TA) under clinical conditions. This study has attempted to determine the efficacy of two such clinically applicable techniques, i.e., viewing a low spatial frequency (approximately 0.1 cpd) difference of Gaussian (DOG) grating or a retinoscope beam in an otherwise dark room. Additionally the accommodative response (AR) was measured in darkness. The data indicate that these clinical techniques did provide a degraded stimulus to accommodation. However, measures of AR recorded when fixating the clinical targets did not correlate with the values of AR obtained in darkness. This lack of correlation suggests that the responses obtained when viewing either the DOG target or retinoscope beam may not represent a veridical measure of TA.

Accommodation, Ocular↗
PubMed1989

Comparison of accommodative adaptation using laser and infra-red optometers.

Previous investigations have reported differences in the rate of decay of accommodative adaptation depending on the form of optometer used to assess dark-focus (DF). This study has used both laser and infra-red optometers to measure pre- and post-task values of DF in 10 subjects. DF was assessed before and immediately after an 8 min near-vision task performed at the subjective near-point of accommodation. Examination of the data from the two optometers revealed significant differences in both magnitude and distribution of pre-task DF. Additionally variations in the post- to pre-task shift in DF were observed between the two methods of assessment. Using the laser optometer, six subjects exhibited positive adaptation following the near-task which was not apparent with the infra-red optometer. The data suggest that both instruments may not be sampling open-loop accommodation; the laser optometer is particularly vulnerable to extraneous influences.

Accommodation, Ocular↗
PubMed1989

Does target orientation influence the accommodative response?

A number of studies have demonstrated that visual responsitivity is optimum when viewing either horizontal or vertical stimuli but is significantly reduced when viewing an obliquely oriented object of regard. Accordingly this study examined the accommodative response in 10 subjects to targets oriented at 45, 90, 135 and 180 degrees to the horizontal. Stimuli were located at distances of 1, 3 or 5 D, and steady-state accommodation was measured subjectively from the right eye using a Hartinger coincidence optometer. The data indicate that, for high contrast, supra-threshold targets, variation in target orientation did not produce any significant change in accommodative response. These results suggest that neural sensitivity for monocular blur-driven accommodation is orientation independent. This finding would imply that accommodation and contrast detection are mediated by dissimilar processes.

Accommodation, Ocular↗
PubMed1988

Accommodative adaptation induced by sustained disparity-vergence.

Pre- and post-task measures of dark focus (DF) were used to assess the response of the accommodative system to within-task disparity-vergence in 10 late-onset myopes (LOM's) and 10 emmetropes. Disparity was induced by 3 and 6 delta base-out prisms imposed during a 3 D near-vision task undertaken for 3- and 10-min periods. Accommodation was measured after the task at 1-s intervals over a 90-s period using an objective infrared optometer to determine post-task regression of DF toward pretask values. After the 3-min task both groups show a reduction in DF adaptation with increasing disparity-vergence. After the 10-min task, disparity continues to have a significant effect on accommodative adaptation in LOM's but not in emmetropes, suggesting diminished prism adaptation in LOM's. The implications of these findings are discussed with regard to both current models of accommodation-vergence interaction and the etiology of late-onset myopia.

Accommodation, Ocular↗
PubMed1988

Assessment of the CA/C ratio in a myopic population.

The convergent accommodation/convergence (CA/C) ratio was measured in 30 subjects comprising 10 late-onset myopes (LOM's), i.e., myopia onset at 15 years of age or later, 10 early-onset myopes (EOM's), and 10 emmetropes. The accommodation loop was opened by two methods: (1) the subject viewed a 0.1-mm diameter spotlight at distances of 33 and 100 cm and (2) the subject viewed near-type (viewing distance 33 cm) through 0.5-mm pinholes. Convergence was stimulated by the introduction of 3 and 6 delta base-out prisms before the right eye and the accommodative response of the left eye was measured using an objective infrared optometer (Canon Autoref R-1). There was no significant difference in CA/C between the three refractive groups with either method. The implications of this finding are discussed with reference to previous work on accommodative convergence/accommodation (AC/A) and disparity-induced accommodation and in relation to accommodation-vergence synkinesis in late-onset myopia.

Accommodation, Ocular↗
PubMed1988

Accommodative adaptation to monocular and binocular stimuli.

Pre- and post-task measures of dark-focus (DF) were used to assess accommodative adaptation induced by a 45-s near-vision task at 33 cm. Adaptation was measured under monocular and binocular conditions for a group of 10 young emmetropic subjects (mean age 21.6 years). The accommodative response was measured objectively using an infrared optometer (Canon Autoref R-1). Post-task DF was sampled immediately after the task at 1-s intervals over a 90-s period. No significant difference in accommodative adaptation was observed between the monocular and binocular near-vision tasks. The implications of this finding are discussed with regard to the oculomotor constituents of the closed-loop accommodative response.

Accommodation, Ocular↗
PubMed1988

The effect of vergence adaptation on convergent accommodation.

This study investigates whether, during a sustained near-vision task, the convergent accommodation (CA) derived initially from the fast (reflex) vergence response is subsequently maintained by tonic (adaptive) vergence. CA was examined during the course of a 3 min near-vision task (viewing distance 33 cm) in 10 emmetropic subjects. Vergence was stimulated by the introduction of a 6 delta base-out prism before the right eye while the open-loop accommodative response of the left eye was measured at approximately 1 s intervals using an objective infra-red optometer. In a control condition the subject viewed the target through a plano lens (0 delta). The accommodation loop was opened by the subject viewing near-type through 0.5 mm diameter pinholes. Pre- and post-task measurement of heterophoria was made using a Maddox rod and prism bar. Regression of post-task heterophoria to the pre-task value indicated that adaptation to the vergence stimulus had occurred. However, there was no significant reduction in induced CA during the task. As the onset of adaptation does not produce any fall in CA, it is concluded that both reflex and adaptive vergence act as a stimulus to CA. This finding is discussed with regard to models of accommodation-vergence interaction.

Accommodation, Ocular↗
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↗
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↗