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M Rosenfield

Publications and source records attributed to M Rosenfield.

At least 19 recordsLinked to original sources
PubMed1992

Factors influencing accommodative adaptation.

Previous studies have ascertained that a broad range of parameters have the facility to induce or modify accommodative adaptation, i.e., the post-task shift in dark accommodation (DA) which may be observed after a period of sustained fixation. This paper reviews the optical (i.e., related to a change in the form of the retinal image) and nonoptical (i.e., independent of the composition of the retinal image) stimuli which can influence the degree of adaptation. It is concluded that DA probably represents an aggregate response resulting from multiple inputs whose interactions may be too complex to allow the isolation and measurement of any single nonoptical component. Accordingly, the exact mechanism of accommodative adaptation remains unclear at the present time.

Accommodation, Ocular↗
PubMed1992

Pharmacological effects on accommodative adaptation.

We review the research which has attempted to determine whether the characteristics of autonomic innervation of ciliary smooth muscle are relevant to the process of accommodative adaptation. The effect of various topical autonomic drugs on the three phases of adaptation were analyzed: pre-task tonic accommodation (open-loop); within-task accommodative response (closed-loop); and post-task regression of accommodation to pre-task tonic levels. Although it is clear that parasympathetic innervation predominates, there is evidence that some individuals utilize supplementary inhibitory sympathetic innervation. When sympathetic innervation is augmented by substantial levels of concurrent parasympathetic accommodative activity, it may serve to attenuate the magnitude and duration of post-task shifts in tonic accommodation. It is proposed that individuals with a deficit in sympathetic inhibition may therefore be predisposed to anomalies of accommodative adaptation. However, the mechanism by which the oculomotor system responds to such predisposition is at present obscure.

Accommodation, Ocular↗
PubMed1992

Contribution of accommodation and disparity-vergence to transient nearwork-induced myopic shifts.

Many investigations have attempted to demonstrate a relationship between sustained near-vision and the aetiology of environmentally-induced myopia, but it remains unclear whether myopic development relates to the actions of either accommodation or vergence. The present study investigated the effect of varying the disparity-vergence demand during a near-vision task while maintaining the accommodative stimulus constant. We required 20 young subjects to perform a near task (viewing distance = 20 cm) for 20 min through base-in, zero power and base-out prisms. The magnitude of the prisms for each individual corresponded to one-third their near vergence range. Pre- and post-task measurements of refractive state were determined objectively using an infrared optometer, with post-task readings being recorded over the initial 50 s following task completion. The results indicated no significant difference between the transient far-point shift for the three disparity-vergence conditions. However, combining data across conditions, a significant, mean shift in the myopic direction of 0.14 D was observed during the 10-20 s period immediately following task completion which dissipated within 20-50 s post-task. These findings suggest that the transient post-task myopic shift was not related to the output of disparity-vergence.

Accommodation, Ocular↗
PubMed1992

Accommodative response during distance optometric test procedures.

The control of accommodation is an essential requirement during the clinical optometric assessment of distance vision. Accordingly, the aim of the present study was to examine the steady-state accommodative response during a number of conventional clinical procedures carried out at a viewing distance of 6m (20 feet). Accommodation was measured subjectively to Snellen letters using a Hartinger coincidence optometer during distance viewing, simulated retinoscopy and following the introduction of cylindrical and prismatic lenses in 13 visually-normal, young adults. No significant change in the mean accommodative response was induced by any of the techniques described, with subjects exhibiting a lead of accommodation of approximately 0.25D for all conditions. The results demonstrate the robustness of accommodation to apparently substantial changes in stimulus conditions.

Accommodation, Ocular↗
PubMed1991

Proximal vergence and age.

A number of previous investigations have suggested that the relative contribution of proximal vergence to the overall vergence response may increase with age. Accordingly the present study has examined the proximal convergence/test distance (PC/T) ratio in a clinical population of 106 subjects ranging from 6 to 47 years of age. PC/T was assessed by comparing accommodative convergence/accommodative stimulus (AC/As) ratios obtained using the gradient and heterophoria techniques. With the former method, the stimulus to accommodation was produced optically using spherical lenses whereas in the latter technique, the change in accommodative stimulus arose from variation in actual target distance. The difference between these two measurements of AC/As reflected the output of proximal vergence. No significant variation in PC/T was observed with increasing age. It is proposed that increased disparity-vergence, rather than proximal vergence, is more likely to compensate for any age-related decline in AC.

Accommodation, Ocular↗
PubMed1991

Accommodative responses to conflicting stimuli.

In this study we examined the monocular accommodative response when subjects (N = 12) simultaneously viewed two overlapping, horizontally and vertically oriented targets located at disparate dioptric distances from the observer. The proximal and distal stimuli were located at dioptric levels of 5 and 3, 3 and 1, or 5 and 1 D, respectively. A broad spectrum of individual responses was observed for all target conditions. Additionally, a significant correlation was observed between the accommodative response when the ambiguous targets were viewed and the response found in the absence of a blur stimulus to accommodation. This finding suggests that when conflicting information is provided to a particular component of accommodation, the relative importance of that component in the determination of the aggregate accommodative response is attenuated.

Accommodation, Ocular↗
PubMed1991

The linearity of proximally induced accommodation and vergence.

This study sought to determine the linearity and amplitude of both proximally induced accommodation (PIA) and vergence (PIV) by comparing the open-loop accommodation and vergence responses, respectively, to individual stimuli located at viewing distances ranging from 0.20 m to 1,500 m. For the measurement of PIA, the vergence and accommodation loops were opened by subjects (N = 10) monocularly viewing the target through a 0.5-mm pinhole, while accommodation was assessed concurrently using an infrared optometer. In the assessment of PIV, the accommodation loop was opened either by subjects (N = 10) viewing a low-frequency difference of Gaussian (DOG) grating or by viewing the targets binocularly through 0.5-mm pinholes. For both PIV methods, the vergence loop was opened by vertical dissociating prisms while the heterophoria was assessed for the various target distances using the von Graefe technique. The results demonstrated significant changes in both PIA and PIV for stimuli located closer than 3 m. However, both proximal components attained a minimum level and remained constant for targets at or beyond 3 m. Furthermore, the magnitudes of PIA and PIV were linearly related to the target distance measured in diopters and meter angles, respectively. These findings clearly demonstrate the influence of target proximity on the oculomotor system.

Accommodation, Ocular↗
PubMed1991

Effect of surround propinquity on the open-loop accommodative response.

The effect of knowledge of surround propinquity, ie, awareness of proximity of the adjacent surroundings, on the open-loop accommodative response (AR) was determined by comparing measurements of accommodation obtained in total darkness in two different-sized rooms. The AR was measured in two laboratories, one 2.5-m square and the other 6.75 x 2.75 m. Steady-state accommodation was assessed on two occasions in each room using an infrared optometer. On the first occasion, the subjects (n = 10) were fully aware of the laboratory dimensions and topography. For the second trial, they were blind-folded before entering the laboratory and hence were unaware of the experimental location. When subjects were unaware of the laboratory dimensions, no significant difference existed between the recorded values of AR. However, when subjects were initially able to observe the size of the room, the AR in darkness was significantly higher in the smaller laboratory. This suggests that proximally induced accommodation, initiated by prior knowledge of the dimensions of the laboratory, was responsible for this increase in AR. Furthermore, it is proposed that complex interactions exist between proximal, tonic, and other nonoptical accommodative stimuli such that it may be impossible to isolate an individual, nonoptical accommodative component.

Adult↗
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↗