Biomedical subjects

M Rosenfield

Publications and source records attributed to M Rosenfield.

At least 37 records · Page 2Linked to original sources

PubMed1995

Effect of age on the interaction between the AC/A and CA/C ratios.

A number of previous studies have examined the effects of age and the development of presbyopia on either the accommodative convergence to accommodation (AC/A) or convergent accommodation to convergence (CA/C) ratios. However, changes in the interaction of these oculomotor crosslinks with increasing age have received relatively little attention, especially over a wide age distribution. Accordingly, the present study examined both crosslink ratios in 42 subjects ranging from 22 to 65 years of age. A dual haploscope-optometer was used to measure accommodation and vergence. The response AC/A ratio showed a small but significant positive correlation with age in those subjects under 45 years of age, while no significant correlation was observed between the stimulus AC/A ratio and age for all subjects. The CA/C ratio exhibited a significant negative correlation with age for all subjects. Furthermore, a trend was observed for lower CA/C findings to be associated with higher response AC/A ratios. However, the two ratios were inversely but not reciprocally related, with the mean difference between the CA/C ratio and the reciprocal of the response AC/A ratio being significantly different from zero. These age-related changes in the output of the oculomotor crosslinks provide further evidence of the continual oculomotor adaptation that occurs concurrent with the loss of accommodative responsivity.

Accommodation, Ocular↗

PubMed1995

Effect of target proximity on transient myopia induced by equidioptric stimuli.

Transient myopia may be exhibited after sustained focus on a near target. This appears to be related to the within-task accommodative response. Although proximally induced accommodation has been shown to produce considerable transient myopia under open-loop conditions, its effect under naturalistic closed-loop conditions remains unclear. Accordingly, the present study examined the effect of target distance on transient myopia for equidioptric stimuli (5 D). A Canon R-1 autorefractor was used to assess the pre- and post-task refractive state objectively. Two tasks were performed monocularly and consisted of either accommodating on a near target at 20 cm (5 D) or a far target at 6 m viewed through a -5 D lens. The former task involved both blur and proximally induced accommodation, whereas the latter consisted of a blur stimulus only. Similar amounts of transient myopia were found under both conditions. These equivalent responses may be related to the relatively small output of proximally induced accommodation believed to be present under closed-loop conditions.

Accommodation, Ocular↗

PubMed1995

Repeatability of subjective and objective refraction.

Although several studies have examined the repeatability of objective refraction, data concerning the repeatability of subjective refraction under masked conditions, i.e., where the examiner is unaware of the refractive results, are limited. Accordingly, the present study compared the variability of both subjective and objective refractive techniques. Refractive error was measured in 12 subjects on 5 separate occasions. Conventional subjective procedures were used, with the exception that the sphere power scale on the phoropter was covered so that the examiner was unaware of the final result. Objective measurements were obtained using a Canon Autoref R-1 infrared autorefractor. The standard deviation (SD) of the five examinations was calculated for each individual and the mean values for the population sample determined. The mean SD's for the subjective and objective techniques were +/- 0.14 and +/- 0.18 D, indicating 95% confidence limits of +/- 0.27 and +/- 0.35 D, respectively. It is concluded that with either assessment technique, a change in refractive error of at least +/- 0.50 D should be adopted as the minimum significant shift in refractive status.

Adult↗

PubMed1994

Accommodative adaptation in children.

Although accommodative adaptation has been studied extensively in young adult populations, there has been little consideration of this function in children. Accordingly, we examined accommodative adaptation by comparing pre- and post-task measurements of dark accommodation (DA) in children and young adults. DA was assessed objectively before and immediately after a 5-min near-vision task (viewing distance = 20 cm) using an open-field, infrared optometer (Canon Autoref R-1). The study was performed on 15 visually normal children (mean age = 10.1 years) and 10 visually normal young adults (mean age = 25.2 years). No significant difference was observed between the mean values of pre-task DA for the two age groups (children = 1.01 D, adults = 0.88 D). Both groups showed equivalent degrees of accommodative adaptation (approximately 1.0 D), and the rate of regression of post-task DA to the pre-task level was similar for each group. We found a significant positive correlation between the magnitude of adaptation and pre-task DA in children, which was not found in the young adult population. The results indicate that pre-task DA and accommodative adaptation (both in terms of magnitude and rate of decay) are similar in adults and children. This would not support the proposal that the development of nearwork-induced myopia in children is related to short-term variations in accommodative adaptation when compared with young adults.

Accommodation, Ocular↗

PubMed1994

Cognitive demand and transient nearwork-induced myopia.

Previous studies have suggested that nearwork-induced myopia may be related to the amount of mental effort and cognitive demand required during the course of near-vision tasks. Accordingly, we compared measurements of the far point of accommodation (FPA) obtained before and immediately after 10-min sustained near-vision tasks involving either low, moderate, or high cognitive demand. All measurements of the FPA were obtained objectively using an open-field infrared optometer. Although a significant myopic shift in the FPA was observed after all conditions, no significant difference was recorded between the three cognitive levels. The mean myopic shift in the FPA immediately after the near-vision task was 0.23 D. It is concluded that the transient, task-induced myopic shift in the FPA is related to the within-task accommodative response rather than to variations in cognitive demand during the course of the near-visual activity.

Accommodation, Ocular↗

PubMed1994

Tonic accommodation: a review. II. Accommodative adaptation and clinical aspects.

Part I of this review considered basic aspects of tonic accommodation (TA), i.e. the accommodative response observed under degraded stimulus conditions. Part II considers accommodative adaptation, i.e. the apparent change in TA following periods of sustained fixation, and clinical aspects of both baseline TA and accommodative adaptation. It is suggested that the apparent post-task shift in TA reflects the slow rate of decay of the stimulus-mediated adaptive accommodative response, while the actual level of tonic innervation to the ciliary muscle remains relatively constant. The clinical implications of both TA and accommodative adaptation are discussed with regard to night, space and instrument myopia and refractive error development, notably nearwork-induced myopia. It is concluded that the evidence for any association between this form of myopia and either TA or accommodative adaptation is equivocal, and furthermore it seems likely that TA plays only a minor role in influencing the closed-loop steady-state accommodative response.

Accommodation, Ocular↗

PubMed1994

Tonic accommodation, tonic vergence and surround propinquity.

Previous studies have typically assessed tonic accommodation (TA) and tonic vergence (TV) by placing subjects in total darkness. However, a recent investigation demonstrated that even under such apparently stimulus-free conditions, subjects' awareness of the proximity of the adjacent surroundings and overall room topography (i.e. surround propinquity) may still influence the accommodative response. Accordingly, the aim of the present study was to measure TA and TV while subjects (n = 34) viewed an illuminated distant target (viewing distance = 6 m) to minimize this propinquity effect. TA was measured using an objective, open-field, infrared optometer under two conditions: first, while viewing the distant target monocularly through a 0.5 mm pinhole, and second in total darkness. Additionally, TV was assessed by determining the heterophoria subjectively while subjects viewed the distant target biocularly through 0.5 mm pinholes. The mean level of TA using the pinhole technique (mean = 0.28 D) was significantly lower than that observed in total darkness (mean = 0.60 D). Furthermore, a significant positive correlation (r = 0.86) was found when comparing the difference between the two TA measurements with the level obtained in total darkness. Those subjects having apparently high levels of TA in darkness exhibited the largest propinquity effect. Thus measurements of accommodation recorded in total darkness are likely to have overestimated both the magnitude and normal range of TA. The mean level of TV was 0.58 metre angle. No significant correlation was observed between TV and either of the two TA measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Accommodation, Ocular↗

PubMed1993

Temporal characteristics of proximally-induced accommodation.

This study sought to determine whether proximally-induced accommodation (PIA) is capable of sustaining an accommodative response over time. Accordingly, the steady-state PIA response was measured during the course of a continuous 5 min stimulus period for targets located at distances of 0.2 or 6 m. The vergence and accommodation loops were opened by subjects (n = 8) monocularly viewing the targets through a 0.5 mm pinhole, while accommodation was assessed using an objective, open-field, infrared optometer. The mean PIA response did not change significantly during the fixation period. This finding suggests that PIA is indeed capable of maintaining a sustained response. This observation is consistent with the constancy of apparent target distance perception during extended fixation of a stationary object of regard under these conditions.

Accommodation, Ocular↗

PubMed1993

Tonic accommodation: a review. I. Basic aspects.

In the absence of an adequate visual stimulus, accommodation adopts an intermediate position of approximately 1 D. Since this position was believed to reflect the level of tonic innervation to the ciliary muscle, this response has been termed tonic accommodation (TA). Part I of this review will consider various aspects of this parameter, including its reference to closed-loop accommodative function and autonomic physiology. In addition, both the methods of measurement and appropriate terminology for this function will be discussed. It is concluded that the response, which becomes apparent under so-called 'stimulus-free' conditions, in fact probably represents an aggregate response resulting from multiple, non-optical stimuli. Thus the designation tonic accommodation may not be appropriate, since it fails to describe accurately the heterogeneous composition of the stimulus-free accommodative response. An associated paper (to be published as part II of this review) will examine accommodative adaptation and both clinical aspects of TA and adaptation of TA.

Accommodation, Ocular↗

PubMed1993

Tonic vergence, age and clinical presbyopia.

The relative contribution of tonic vergence to the maximum near vergence response as a function of age and the development of presbyopia has received little attention. Tonic vergence position was measured subjectively in a group of 50 subjects between 20 and 68 years of age. While there was no progressive trend with age, tonic vergence did exhibit a small but consistent convergent increase after 40 years of age. Thus, tonic vergence showed a slight change, possibly of a motor adaptive nature, concurrent with increasing age and the development of clinical presbyopia.

Adult↗

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↗