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Biomedical subjects

M Rosenfield

Publications and source records attributed to M Rosenfield.

At least 19 recordsLinked to original sources
PubMed1997

Irlen lenses do not improve accommodative accuracy at near.

The purpose of the experiment was to determine the influence of Irlen lenses on steady-state accommodation in successful users, as there is speculation that near accommodative dysfunction may be a factor in these patients. Monocular steady-state accommodation in six successful Irlen patients was assessed for near blur stimuli (2, 3, and 4 D) either with nonfiltered spectacle refractive correction or their spectrally broad-band filtered spectacle refractive correction. Accommodation was measured subjectively using a Hartinger coincidence optometer. There was no significant difference in mean level of accommodation between the two conditions. Additionally, there was a small but significant increase in accommodative variability with the filtered prescription. The use of Irlen correction did not have any positive effect on monocular steady-state accommodation at near.

Accommodation, Ocular↗
PubMed1997

Tonic vergence and vergence adaptation.

In the absence of an adequate visual stimulus, the eyes are typically converged by approximately 0.25 to 0.75 meter angles (MA). This vergence response (VR) was believed to reflect the level of tonic innervation to the extraocular muscles, and accordingly has been termed tonic vergence (TV). However, this estimation fails to consider the magnitude of the anatomical position of rest. The true typical value of TV is approximately 23 degrees. This paper will consider various aspects of this parameter, including both clinical and laboratory methods of measurement, and the relationship between TV and the distance heterophoria. In addition, the role of vergence (or prism) adaptation, i.e., the apparent change in TV after periods of sustained fixation, is discussed. This shift appears to result from the relatively prolonged decay of the slow fusional vergence response (VR), with no evidence for a change in the level of tonic innervation. On occasion, the decay of slow fusional vergence may take hours or even days to reach completion. This extended rate of decay will have a significant impact upon the clinical measurement of a number of binocular parameters, most notably the assessment of heterophoria under truly dissociated conditions (i.e., in the absence of any fusional VR). Furthermore, both the magnitude and rate of decay of vergence adaptation appear to vary with age, as well as the presence of oculomotor imbalance. It is concluded that the output of the slow fusional vergence mechanism, as reflected by the degree of vergence adaptation, makes a major contribution to the aggregate, sustained VR in most visually normal patients.

Adaptation, Ocular↗
PubMed1997

Effect of contralateral fog during refractive error assessment.

BACKGROUND: When assessing refractive error using static retinoscopy, it is conventional to fog the contralateral eye by approximately 2.00 D to prevent a blur-driven accommodative response stimulating consensual accommodation in the tested eye. However, the effect of higher amounts of contralateral fog (e.g., in a moderate-to-high uncorrected myopic individual) during refractive error assessment is unclear. METHODS: We assessed the refractive state in 16 visually normal myopic subjects while fogging the contralateral eye between zero and 6.00 D, in 1.00 D increments. Retinoscopy was simulated by shining a streak retinoscope light into the right eye, while simultaneously measuring the refractive state of this eye objectively. RESULTS: No significant change in mean refractive state was observed for up to 5.00 D of contralateral fog. But, 6.00 D of contralateral fog produced a significant mean increase in the myopic direction of 0.13 D. Also, in three subjects, a myopic shift of approximately 0.60 D was recorded after the introduction of 6.00 D of contralateral fog. Nevertheless, the magnitude of these largest shifts in refractive error are still smaller than the previously reported degree of repeatability of static retinoscopy. CONCLUSIONS: Since large amounts of contralateral fog produced only small and clinically insignificant changes in the refractive state, the practitioner merely needs to ensure that the nontested eye is indeed fogged. The magnitude of fog present will have only a minimal effect on the final result.

Adult↗
PubMed1997

The AC/A ratio, age and presbyopia.

Previous reports concerning the effect of age on the AC/A ratio have been equivocal. Therefore, the present study investigated both the stimulus (AC/As) and response (AC/Ar) ratios using a subjective haploscope-optometer in a relatively large sample of subjects (n = 42) over a wide range of ages (22-65 years). The AC/As showed a small but significant decrease with age (approximately 0.04 delta/D/year). When the older subjects (> 45 years of age) were excluded, however, there was no systematic age effect. The AC/Ar exhibited a small but significant increase with age (approximately 0.08 delta/D/year) for subjects under 45 years of age. However, when the older pre-presbyopes and younger presbyopes (35-44 years of age) were excluded, there was no systematic age effect. In subjects 45 years of age and older, the AC/Ar could not be reliably assessed. This was attributed to physiological and instrumentation noise as a result of the minimal change in accommodative response. In the mid-aged subjects (35-44 years of age), the apparent increase in AC/Ar with age was speculated to be due to neural adaptation of the crosslink gain from the accommodative to the vergence system and/or slight intrusion into the upper non-linear response region of accommodation with the measurements. The finding of AC/Ar constancy with age when mid-aged pre-presbyopes and early presbyopes were excluded supports the non-linearity hypothesis, and thus there appears to be no real change in AC/Ar with increased age. The results support the Hess-Gullstrand theory of presbyopia.

Accommodation, Ocular↗
PubMed1997

Effect of prolonged dissociation on the subjective measurement of near heterophoria.

Previous studies have demonstrated that vergence adaptation resulting from the prolonged decay of slow fusional vergence may prevent the accurate assessment of oculomotor deviations. Continuing changes in heterophoria have been reported after 27 days of monocular occlusion. However, since most slow fusional vergence will decay within the first few minutes of dissociation, a clinical assessment of both vergence adaptation and heterophoria could be made more rapidly. This report documents two investigations which examined changes in near horizontal heterophoria during 30 min and 180 min of continuous dissociation, respectively. Seven out of the 16 subjects exhibited significant changes in heterophoria during the 30 min dissociation period, with a mean increase in exophoria of 3.4 delta. The decay of slow fusional vergence took approximately 25 min to reach completion. Thus in the clinical setting, both the degree of vergence adaptation and a more accurate assessment of heterophoria may be obtained by maintaining dissociation for 25 min. Furthermore, the presence of vergence adaptation can be assessed after just 5 min of dissociation.

Adult↗
PubMed1996

Comparison of clinical techniques to assess the near accommodative response.

Assessment of the accommodative response (AR) is an essential part of the optometric examination. This study compared a number of clinical procedures for determining the AR with the findings of an objective infrared autorefractor. First, the AR to a 2.5 D binocular stimulus was measured by dynamic retinoscopy (neutralization being obtained both with lenses and by varying the working distance), dynamic cross-cylinder (with and without fogging lenses), and a near red-green duochrome test. Second, the response to a monocular 2.5 D stimulus was examined using dynamic retinoscopy (neutralizing with lenses), dynamic cross-cylinder, and the red-green duochrome. Third, the monocular AR was examined with both red-green and blue-yellow near duochrome tests. Under binocular conditions, the mean ARs for all the tests were clinically equivalent. However, comparison with the findings from the objective autorefractor indicated that dynamic retinoscopy (where neutralization was obtained by varying the working distance) showed the closest agreement, whereas the two dynamic cross-cylinder procedures exhibited the greatest variability. For the monocular condition, the mean lag of accommodation observed with the autorefractor was significantly less than that observed with dynamic retinoscopy, the dynamic cross-cylinder, or the red-green duochrome. However, the blue-yellow near duochrome test did not provide a valid estimation of the AR. It is concluded that the technique of dynamic retinoscopy where the working distance is varied to obtain a neutral reflex should be the method of choice for the clinical assessment of the AR, because this procedure does not require the introduction of supplementary lenses, which may themselves alter the AR.

Accommodation, Ocular↗
PubMed1996

Proximal contribution to a linear static model of accommodation and vergence.

To determine the influence of target proximity on accommodation and vergence under both open- (OL) and closed-loop (CL) viewing conditions, a static interactive feedback model, which included proximal accommodation (PA) and proximal vergence (PV) inputs, was developed and analysed quantitatively. It was based on an earlier static dual-interactive feedback model of accommodation and vergence. The proximal inputs were added to both the accommodative and vergence loops at the output of the respective controllers. The values of the PA and PV gains were obtained from experimental dual-OL data. The model equations were analysed over a stimulus range of 1 to 6 D (or MA). It was found that under the dual-OL condition, the contribution of PA to the overall accommodative output ranged from 42.5 to 81.6%, whereas the contribution of PV to the overall vergence output ranged from 56.1 to 88.5%. In contrast, under all other stimulus conditions, with the exception of the PA contribution to the accommodative output under the Aol, Vcl condition (26.5-41.0%), the relative contributions were much smaller, ranging from 0.04 to approximately 7.0%. In particular, under the dual-CL condition, representing the normal binocular visual feedback condition, the relative contributions were only 4.0 and 0.04% for PA and PV, respectively. Thus, although the relative contributions of PA and PV were large under the dual-OL condition, they were generally very small under the various CL conditions that simulated more naturalistic viewing situations. Nevertheless, proximity may still play an important role by providing cues for attaining coordinated and harmonious motor responses under specific viewing conditions.

Accommodation, Ocular↗
PubMed1996

Multi-meridional keratometry.

During conventional keratometry, the two principal meridia are identified and measurements of the anterior corneal curvature determined along these orientations. However, in cases of corneal irregularity, the principal meridia may be difficult to identify. Accordingly, the present study sought to evaluate two alternative procedures which do not require identification of the principal meridia. Instead, measurements of anterior corneal curvature were determined along either three or four preselected meridia and subsequently converted into the standard format for measurements of anterior corneal curvature. The study was performed on 25 visually normal subjects and the results compared with conventional two meridian keratometry findings. No significant differences were observed between the mean findings for the three and four meridian techniques. Furthermore, both procedures gave comparable results to the conventional two meridian method. Accordingly, multi-meridional keratometry may be valuable in cases of irregular astigmatism, for example produced by keratoconus or scarred corneas, since measurements can be obtained without the necessity for identification of the principal meridia.

Cornea↗
PubMed1996

Repeatability of clinical measurements of the amplitude of accommodation.

In order to determine whether a significant change has occurred in a clinical parameter, it is essential to assess the repeatability of the measurement procedure. Accordingly, the present study has examined the repeatability of three techniques for evaluating the subjective amplitude of accommodation. Clinical amplitudes were determined using the push-up, push-down and minus lens procedures in 13 young individuals (mean age: 24.3 years) on five separate occasions. The standard deviation (SD) of the five examinations was calculated for each individual and the mean values for the population sample determined. The mean SDs for the push-up, push-down and minus lens techniques were equivalent, with 95% confidence limits of approximately 1.4 D being observed for all three procedures. Furthermore, the mean amplitude recorded using the push-up technique was significantly higher than that observed for the other two procedures. It is concluded that a change of at least +/- 1.50 D should be adopted as the minimum significant shift in amplitude of accommodation for this group.

Accommodation, Ocular↗
PubMed1995

Vergence adaptation and the order of clinical vergence range testing.

When measuring horizontal relative vergence ranges, the conventional clinical procedure is to assess the base-in (or divergence) range before the base-out (or convergence) determination. The rationale for this order of testing is that the convergence responses stimulated during the base-out measurements may produce vergence adaptation (i.e., a fusional aftereffect), which may temporarily bias the subsequent base-in values in the base-out direction. However, the effect of reversing this order of testing (i.e, base-out before base-in) has not been directly evaluated. Accordingly, the present study compared distance base-in vergence ranges measured both before and after base-out testing at separate test sessions. Additionally, tonic vergence (TV) was assessed before and after each vergence range measurement. The results indicated that base-out vergence range testing stimulated vergence adaptation, and furthermore produced a statistically significant reduction in the subsequently measured base-in recovery value. However, the magnitude of this shift was less than the estimated degree of repeatability of the vergence range measurement. Therefore, a more appropriate order of testing would be to assess the heterophoria compensating range first in order to obtain accurate results during this more critical measurement.

Adaptation, Ocular↗
PubMed1995

Do changes in pupil size and ambient illumination affect the duochrome test?

Vague and conflicting suggestions currently exist within the literature regarding the appropriate level of ambient illumination to use while conducting the clinical duochrome (bichrome) test. One proposal is that reduced illumination should be adopted since this allows the pupils to dilate, thereby increasing the chromatic interval and resultant test sensitivity. The aim of the present study was to determine whether changes in pupil size and ambient illumination do indeed alter the subjective duochrome response. Accordingly, eight young, visually normal subjects were dilated with 2.5 percent phenylephrine and tested while monocularly viewing the duochrome chart through 1, 3, 5 and 7mm artificial pupils. Additionally, the effects of performing the test through a 1.0 log unit neutral density filter and varying the overall room illumination were examined. There were no significant differences between the mean responses under all test conditions. The variability of individual responses decreased with increasing pupil size; however, a 4mm change in pupil diameter was required to alter the response variability significantly. Therefore it is recommended that the test be performed under the minimum practical ambient illumination conditions in order to minimize this variability.

Accommodation, Ocular↗
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↗