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Biomedical subjects

R W Reading

Publications and source records attributed to R W Reading.

At least 19 recordsLinked to original sources
PubMed1994

Variations in the monocular components of fixation disparity.

Measurements of the monocular components of fixation disparity through small amounts of lateral prism show changes in the proportional contribution of each eye with changing vergence stimuli. Prism does not usually alter the independence of the activity of each eye during binocular viewing. This independence allows the monocular shares to fluctuate from moment to moment. Responses to prism include fixating with one eye or the other, shifting both eyes laterally in the same direction, and distributing the deviations between the two eyes. Some of these strategies reduce the deviation and are therefore adaptive. Others appear to maintain a fairly stable state which frequently involves resorting to the equivalence of a monocular form of localization. Prism adaptation follows decidedly different time courses and occurs to differing extents for the different subjects and for the different conditions tested. It is not uncommon for many of these changes to occur unilaterally. Voluntary activity seems to be an important factor in the processes associated with adaptation to prism.

Fixation, Ocular↗
PubMed1992

Vergence errors: some hitherto unreported aspects of fixation disparity.

Measurement of the monocular components of fixation disparity indicated a higher prevalence of asymmetric contributions to the total deviation than previously reported. Furthermore, the exact proportion varied from moment to moment. Two of six subjects showed significant changes in fixation disparity over a period of 1 week. For all six subjects the changes in fixation deviation of one eye were virtually independent of those changes occurring in the other eye. In other words, these monocular variances were uncorrelated. Settings of the monocular components of binocular fixation disparity were accomplished at an accuracy close to that achieved by using a monocular vernier technique. The remaining differences appeared to be due to occasional instabilities during binocular viewing. The usual method of clinical measurement in which only one element is moved is not always equivalent to that determined by summing the two monocular components. The principal process measured by subjective fixation disparity appears to be either oculomotor or localized directional shifts of a monocular nature.

Convergence, Ocular↗
PubMed1989

Comparison of two fixation disparity determinantions.

Fixation disparity values derived from horopter measurements are compared with those determined using the disparometer on seven subjects wearing lateral prisms. Although the two measures are intrinsically different, five subjects showed similarity in the form and position of the two fixation disparity-forced vergence functions. Two subjects manifested fixation disparities that indicated the use of proximal or voluntary control of relative eye position for both base-out and base-in forms of lateral prism. Another subject showed a paradoxical response to base-out prism that could be attributed to recovery from previous application of base-in prism, adaptation to base-out prism, or both. An additional subject showed irregular alterations in vergence posture during nonius horopter measurements. The clinical implications of vergence responses other than those associated with fusion and accommodation are discussed and the effect of this form or eye movement control is related to the change in position and shape of the equidistance horopter when it is measured through lateral prism.

Fixation, Ocular↗
PubMed1986

Nonius horopter in projected viewing.

Nonius horopter measurements were made on three normal subjects using both physically displaced (real viewing) and stereogrammetrically displaced (projected viewing) test objects. Three subjects with ocular anomalies were tested using the projected viewing arrangement with and without 5% overall magnifier before the right eye, and seven complete measurements of the projected viewing horopter were made on a fourth subject with an ocular anomaly over the period of 1 month. These latter individual plots showed large irregularities that changed location from day to day. Plotting the mean and standard error of the means of these seven sets of data produced a smoothing out of the horopter locus. Plotting each individual horopter setting in the sequence of measurement and monitoring eye position indicated that all of the irregularities and regional horopter changes found are most likely introduced by changes in fixation disparity (vergence eye movements).

Depth Perception↗
PubMed1986

Vergence instabilities and the longitudinal horopter.

The method of averaging was applied to the results of repeated measures of the longitudinal horopter for four subjects classified as binocularly normal and one anisometropic amblyope. The results produced a refined horopter locus and suggested that the so-called Vieth-Mueller circle is an adequate describer of the empirical longitudinal horopter, except in those cases involving uncorrected aniseikonia.

Amblyopia↗
PubMed1985

Determinations of the horopter in esotropia.

Eight binocularly abnormal subjects, including 5 esotropes, made successive horopter settings on several different days. The individual data frequently showed irregularities that were not always repeatable, most likely due to vergence instabilities. However, the mean standard error of the means of several replications produced a more nearly smooth horopter locus. Some of the subjects showed a tendency to make settings to the right of the straight ahead that were displaced proximally (eso disparity). It would appear that repeated measures can be useful in neutralizing the effect of extraneous changes in eye position, provided that these are not too large. The strabismus horopter is most likely very similar in shape and location to that found in the normal.

Adult↗
PubMed1985

The longitudinal horopter in exotropia.

The method of repeated measures was applied to a group of 4 exotropes in order to test the hypothesis that irregularities in their day-to-day longitudinal horopter findings were caused by random horizontal vergence eye movements. Determining the mean of several sets of replications smoothed out the horopter. Horopters in exotropes appear to be very similar to those found in normal binocular subjects.

Aged↗
PubMed1985

Horopter deviations and distortions.

Previously gathered data from 3 subjects, judged to show usually very steady binocular fixation, were selected for retrospective analysis. This consisted of determining the means and standard error of the means of as many control runs as were available. The role of the fluctuation of vergence eye movement responses in producing the results is discussed. It is concluded that the longitudinal horopter most likely always conforms to the locus of a circle constructed through the two entrance pupils and the point of fixation.

Aniseikonia↗
PubMed1985

Prism-induced horopter distortions.

The effects that lateral prisms have on the horopter were evaluated in 11 subjects, including 6 subjects classified as binocularly abnormal. For normal subjects with good stereopsis the equidistance (stereoscopic distance matching) horopter shape was altered with the application of lateral prism. For other subjects this was not the case. Equidirection (nonius) horopters were unchanged by the application of lateral prism in all of the subjects tested. In addition to localized irregularities in the horopter locus, shifts in fixation disparity produced regional distortions of the horopter.

Depth Perception↗
PubMed1984

Horopter shifts due to a magnification change.

Both the equidirection ( nonius ) and the equidistance horopter criteria were used on a group of subjects with and without the application of a 5% overall magnifier before the right eye. For three of six subjects, shifts in the equidirection horopter induced by this afocal lens could not be predicted on the basis of the magnification properties of the lens and the assumption that corresponding points are fixed. Equidistance horopter plots showed reasonably systematic reductions in slope between the predicted and the measured values for all subjects. Irregularities in all data were accounted for by shifts in the vergence angles during the experiment.

Aniseikonia↗
PubMed1983

A comparison of two horopter criteria.

Both the binocular nonius and classical nonius criteria were applied to a group of subjects in order to compare the resulting horopters. Results indicated that monocular visual directions shifted along with changing binocular disparities when using the binocular nonius technique. This method constitutes a modification of the frontal plane criterion, since binocular portions still can be set equidistant to the fixation object. Comparing equidistance (binocular nonius) with equidirection (nonius) indicated that the 2 loci were essentially the same. Shifts in the nonius horopter induced by a small overall magnifier could not be predicted for 2 out of 7 subjects; one of these with aniseikonia and the other with intermittent exotropia. Irregularities in all horopter data could be accounted for by shifts in the vergence angles during the experiment.

Aniseikonia↗
PubMed1983

Possible alterations in correspondence associated with asymmetric convergence.

Available nonius horopter data in asymmetric convergence has been reanalyzed by computing the binocular disparity of each horopter datum point relative to the Vieth - Müller circle. The results of this analysis on the best available data indicate that some corresponding points do shift upon asymmetric gaze. Because such convergence postures involve different eye movement innervational patterns, it is suggested that this is the cause of these apparent alterations. Some of the remaining data showed nonsystematic changes in experimental errors, suggesting that unintentional shifts in fixation may have occurred; unintentional tactile cues (used in making the actual settings) may have been present; and sampling errors may have influenced these particular findings.

Eye Movements↗
PubMed1982

Finely graded binocular disparities from random-dot stereograms.

Rotation of a stereogram around an axis through its centre provides a method of presenting finely graded binocular disparities. Such displays are useful for clinical testing of stereopsis. A comparison between projected- and real-depth thresholds indicated that most of the differences could be accounted for in terms of the change in stereoscopic sensitivity associated with differing errors in the equidistance judgements. The method of disparity display described allows for the direct observation of those attributes of random-dot stereopsis known as global stereopsis and local stereopsis and requires caution in comparison of stereopsis thresholds using these different perceptual criteria.

Adult↗
PubMed1981

A disparity analysis of the anomalous correspondence horopter.

Some of the data of Flom and that of Boucher are analyzed using binocular disparity analysis in order to show the resulting apparent changes in horopter disparities in patients with anomalous correspondence brought about by alternate monocular fixation, binocular fixation, surgery, and prism. The problem of eye movements during horopter determinations is discussed.

Aniseikonia↗
PubMed1980

A disparity analysis of some horopter data.

A form of binocular disparity analysis has been applied to some grid nonius, apparent frontoparallel plane, diplopia limit, and binocular nonius data from studies by Ogle and Ames et al. The results show that all horopter criteria are capable of detecting fixation disparity and indicate that the apparent frontoparallel plane can change shape and position as a result forced vergences. The effect of size lenses, plus lenses, and fixation distance are discussed. A comparison between the disparity analysis of partition data and horopter data is presented.

Data Collection↗
PubMed1980

The threshold of stereopsis in the presence of differences in magnification of the ocular images.

A comparison between 100 percent correct response thresholds of stereopsis for nine subjects measured with and without viewing using a 33 percent difference in ocular image magnification is presented. Two subjects performed threshold settings, using the method of adjustments, with 1, 5, 10, 15, and 33 percent magnification differences. The extent of the increase explains reports of stereopsis in corrected unilateral aphakia.

Adult↗
PubMed1978

Panum's area explained in terms of known acuity mechanism.

Comparisons between the various types of binocular and monocular visual acuity thresholds are made in this study. The results obtained in monocular resolution and binocular diplopia experiments support LeGrand's view regarding Panum's area. Thus the physiological mechanism which appears to account for both monocular resolution and binocular diplopia thresholds could also account for a spatial tolerance which gives rise to Panum's area.

Depth Perception↗