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At least 19 recordsLinked to original sources

PubMed2002

Interexaminer repeatability of a new, modified prentice card compared with established phoria tests.

PURPOSE: The Howell phoria card, a new modification of the Prentice design, has no previously published validity or reliability data. The purpose of this study was to compare the interexaminer repeatability of the Howell phoria card with established tests. METHOD: Experienced optometrists measured the near heterophoria of 72 subjects. Heterophoria was measured in a pseudo-random order using five standardized procedures: (1) Howell phoria card continuous presentation, (2) Howell phoria card flashed presentation, (3) free-space von Graefe method, 4) Bernell Muscle Imbalance Measure (MIM) card continuous presentation, and (5) MIM card flashed presentation. RESULTS: The von Graefe method and the Howell phoria card flashed presentation found significantly less exophoric results than the MIM card. There was no consistent tendency for different examiners to find more exo- or more esophoric results with the phoria measurement techniques used in this study (p = 0.28). Both the Howell phoria card continuous presentation and the MIM card had significantly less variability in interexaminer differences than the Howell phoria card flashed presentation and the von Graefe method (p < 0.05). CONCLUSIONS: Results from this study suggest that the Howell phoria card used in a continuous presentation method has an interexaminer repeatability that is not significantly different from the MIM card but greater than the von Graefe method.

Adult↗

PubMed1998

Asymmetrical vertical phorias indicating dissociated vertical deviation in subjects with normal binocular vision.

We measured the symmetry of phoria angles in six normal subjects. Subjects were selected on the basis of good visual acuity and stereopsis, normal binocular eye alignment and, apart from mild refraction errors, absence of ocular abnormalities. They were instructed to look at a word on a reading chart at 2 m distance. Each measurement consisted of five subsequent intervals of 5 s duration. During these five intervals viewing was binocular, with the right eye only, binocular, with the left eye only, and binocular, respectively. Each experiment consisted of twelve measurements. Eye movements were measured with scleral coils suited for measuring in horizontal, vertical and torsional directions. Five out of six subjects displayed an asymmetrical vertical phoria; one subject showed an alternating hyperphoria; four displayed a left over right vertical phoria that was largest for left eye occlusion. Only one subject showed a symmetrical vertical phoria. Both the size of the vertical phorias and the size of the asymmetries in these vertical phorias were very small: on average 0.16 +/- 0.01 and 0.17 +/- 0.01 degree, respectively. The direction of the vertical phoria asymmetries (the largest left over right was found with left eye occlusion) and the fact that asymmetries were found more often in vertical than horizontal and torsional phorias suggest that these asymmetries are related to dissociated vertical deviation. These results suggest that dissociated vertical deviation, often observed in subjects with a disruption of binocular vision early in life, reflects the enhancement of a phenomenon that is present in normal subjects as well.

Adult↗

PubMed1992

Role of monkey midbrain near-response neurons in phoria adaptation.

1. One striking characteristic of the way in which accommodation and convergence of the eyes are organized is that although the two responses are usually tightly coupled, a brief period of binocular viewing through prisms that require extra convergence brings about a persistent, adaptive alteration in the relationship between the two responses: the vergence during monocular viewing of a target at a given distance is biased in a convergent direction. We sought to discover the role of the near-response neurons we have previously described in the monkey midbrain in such phoria adaptation. 2. Phoria adaptation was produced in two monkeys by having them view binocularly stereoscopic targets under conditions that mimicked prism viewing, i.e., the mirrors of the stereoscope were set so as to require more convergence than that associated with a real target at the same distance as the images seen in the stereoscope. The activity of 57 near-response neurons located dorsally and dorsolaterally to the oculomotor nucleus was recorded before and after adaptation while the monkeys monocularly viewed targets at a range of distances. 3. Comparison of a neuron's response in normal binocular viewing with the response when the accommodation and vergence stimuli were in conflict allowed us to distinguish 24 neurons that behaved as though they were related exclusively to the vergence response. 5 neurons that behaved as though they were exclusively related to the accommodation response, and 12 neurons whose firing was not so simply related to either response. We were unable to classify the remaining 16 near-response cells by this method. 4. In accommodation-related neurons, the relationship between firing rate and accommodation did not alter, or only altered slightly, when the animal's phoria was adapted. 5. The relationship between firing rate and vergence was unaltered by phoria adaptation in only a small proportion of vergence-related neurons, showing that most neurons do not carry the entire signal responsible for phoria adaptation. On the other hand, in the majority of vergence-related neurons the relationship between firing rate and accommodation was altered by phoria adaptation, showing that most neurons do carry part of the phoria adaptation signal. 6. The implication is that the increase in vergence observed after adaptation is mediated at more than one site. A proportion of the phoria adaptation signal is present at the level of the midbrain vergence-related neurons, with the remainder of the signal being added later, presumably at the motoneurons.

Accommodation, Ocular↗

PubMedDate not supplied

Characteristics and variability of vertical phoria adaptation in normal adults.

We evaluated the characteristics of phoria adaptation for vertically induced retinal disparity. An adaptive change in the fusion-free ocular alignment, phoria adaptation, was measured with a computer-aided mirror haploscope at 10, 30, and 60 minutes after the start of wearing of a 3-prism-diopter base up prism by 35 normal subjects ranging in age from 21 to 67 years (mean: 37 years). The relationships between phoria adaptation and the subjects' age, the vertical fusional amplitude, the amount of heterophoria, and the starting time of the examination were evaluated. All subjects showed phoria adaptation, with the mean (+/- SD) degree of 0.78 +/- 0.28 degree, 0.96 +/- 0.26 degree and 1.02 +/- 0.30 degrees at 10, 30, and 60 minutes, respectively, after wearing the prism. The repeatability (95% confidence interval) for the measurements was less than +/- 0.24 degree. There was a significant correlation between the vertical fusional amplitude and the gain of phoria adaptation (at 10 and 60 minutes, P < 0.05). The gain of phoria adaptation measured at 60 minutes showed a significant decrease with age (P < 0.01). The results indicate that the time course of phoria adaptation in the vertical direction is similar to that in the horizontal direction and its gain differs considerably among subjects.

Adaptation, Ocular↗

PubMed1999

Nearpoint phoria changes associated with the cessation of childhood myopia progression.

BACKGROUND: A convergent (eso) shift in near phoria associated with the onset of myopia has been reported. METHODS: Data from two Midwestern United States optometry practices were used to assess whether the near phoria shifted back in the divergent (exo) direction after the cessation of childhood myopia progression. Data were collected for myopic children who had three or more examinations before the age of 15 years and at least one examination after the age of 17 years. RESULTS: Refractive error data were used to calculate an index of the age of cessation of childhood myopia progression. The phoria at the first examination after the cessation age was designated as the baseline and was normalized to zero. For all previous and subsequent examinations, the changes in phoria with respect to the baseline phoria were calculated. The phoria at the examination just after the cessation age was significantly more divergent than those at the first, third, and fourth examinations prior to the cessation age (1.1, 1.4, and 1.7 prism diopters, respectively). The third visit after the cessation age was 1.8 prism diopters more divergent than the first visit after the cessation age. Thus, these data showed an exo shift in near phoria after the cessation of childhood myopia progression.

Adolescent↗

PubMed1992

Lateral phoria at distance: contributions of accommodation.

Lateral heterophoria at distance often is cited as an index of tonic vergence, yet recent research has shown that vergence in darkness is more convergent than most measures of phoria. Two experiments were conducted to investigate the possible role of accommodation in this discrepancy. Experiment I compared measures of distance phoria of 19 young adults with measures of vergence and accommodation of the same subjects. Dark vergence was found to be correlated with but significantly more convergent than distance phoria. Hierarchical regression analysis showed that individual measures of phoria were related to subjects' negative accommodation (from the dark focus to the distant target) as well as to dark vergence. Experiment II tested 13 young adults to evaluate three simple models of the influence of accommodation on distance phoria. Distance phoria was predicted best by a model that included the subjects' negative accommodation, accommodative vergence, and dark vergence. These findings support the hypothesis that distance phoria is influenced by accommodation for the fixation target. Dark vergence is a simpler index of tonic vergence.

Accommodation, Ocular↗

PubMed1999

The influence of heterophoria measurements on subsequent associated phoria measurement in a refractive routine.

The influence of measuring heterophoria on a subsequent associated phoria measurement was investigated in 50 subjects. After refraction, heterophoria was measured by either von Graefe's technique or Maddox rod and wing. The effect of these procedures was assessed by associated phoria measurements taken before and after the dissociated measures. It is shown that subjects with a history of unstable binocular vision are likely to have an associate phoria induced or changed by the previous dissociated phoria measurement, particularly if von Graefe's technique is employed. It is recommended that, especially for near, associated phoria should be assessed before the dissociated phoria in subjects who are regarded as having a history of unstable binocular vision.

Adult↗

PubMed1996

Reliability of and comparisons among methods of measuring dissociated phoria.

Many methods of heterophoria measurement are available clinically. This paper reviews several studies which have examined the reliability of phoria measurements, and have compared various tests of phoria measurement. Different methods of data analysis make comparison of studies difficult. Two studies indicated 95% limits of agreement of 2 to 4 delta for reliability of modified Thorington, von Graefe, and Maddox rod phoria tests. Studies using correlational analysis to compare different measurement methods have found a high degree of association of the results of these methods. Studies using statistical methods assessing the agreement of test results found a high level of agreement among some tests and a low level of agreement among some tests. Some of the various phoria measurement methods differ in the technique used for dissociation, in the ability to control accommodation adequately, in the level of proximal convergence induced, or in the method by which the phoria is quantified. These differences can result in different phoria measurements on the same patient.

Humans↗

PubMed1998

Development of phoria in children.

BACKGROUND: Although the prevalence of phoria in adults is well documented, data are scarce on phoria in children. We present results using modified clinical technique vision screening and data from the Orinda Longitudinal Study of Myopia on a large, population-based sample of nonstrabismic children to document the prevalence of phoria with age. METHODS: We collected cross-sectional (N = 1495) and longitudinal (N = 469) data. Phoria data were collected by cover tests administered by one observer who subjectively classified phoria as orthophoria, esophoria, or exophoria in 2 delta steps. RESULTS: Ninety-seven percent of the children were orthophoric at distance, and there were no significant changes with age. Near phoria showed a more normal distribution, with a 10.8% decrease in the prevalence of exophoria (from 31.8 to 21.0%) and a 5.5% increase in the prevalence of esophoria (from 6.7 to 12.2%) between kindergarten and fifth grade. CONCLUSIONS: Children are typically orthophoric or exophoric at near, but convergent shifts occur with age.

Child↗

PubMed1993

Interactions between short-term vertical phoria adaptation and nonconjugate adaptation of vertical pursuits.

We have demonstrated that short-term vertical position-specific phoria adaptation contributes to nonconjugate adaptation of vertical pursuits, but not to nonconjugate adaptation of vertical saccades. Binocular adaptation to multiple stationary vertical disparities resulted in both nonconjugate pursuits and phoria aftereffects but had little effect on the early step component of vertical saccades. Similarly, binocular nonconjugate adaptation of vertical pursuits produced both nonconjugate pursuits and fixation phoria aftereffects. Position-specific adaptation of nonconjugate pursuit was demonstrated by adapting to disparate motion in the upper field which resulted in nonconjugate pursuit aftereffects that were greater in the upper than the lower hemifield. These nonconjugate pursuits were accompanied by position-specific phoria aftereffects, indicating that common mechanisms underlie adaptation of vertical phoria and nonconjugate pursuits.

Adaptation, Ocular↗

PubMed1994

Mechanisms of vertical phoria adaptation revealed by time-course and two-dimensional spatiotopic maps.

The spatial spread of short term phoria adaptation was measured in response to either a single vertical disparity presented at a single eye position, or, vertical disparities of opposite sign presented at two different locations along either the primary vertical or horizontal meridians or along an oblique axis. The spread of adaptation to eye positions not specifically adapted was assessed by measuring phoria across a two-dimensional surface. The change in phoria was uniform across the field in response to a single disparity. With two disparities, adaptation conformed to the stimulus demand in the direction in which the disparity varied but was uniform in the orthogonal direction. The time-course of the adaptation indicated the presence of two mechanisms, a global one which shifted the phoria uniformly across the field and a local one which selectively adjusted the phoria to the position dependent demands of the disparity stimulus.

Adaptation, Ocular↗

PubMed2001

The effect of saccades and brief fusional stimuli on phoria adaptation.

PURPOSE: The purpose of this experiment was to determine whether brief fusional stimuli and saccades similar to those seen in the alternate cover test affect phoria disadaptation. METHODS: Three cover test conditions were performed randomly. Before each test condition, subjects fused for 2 min at an angle convergent to the subjective phoria. In one test condition, subjects viewed monocularly. In another condition, subjects alternately fixated with each eye (no binocular time). In a third condition, subjects alternately fixated with each eye, and there was a 100-ms period of binocular viewing between alternations. The ocular vergence angle was monitored using scleral search coils. RESULTS: Vergence angle was plotted against time for each condition. The area under this plot was determined using a computer program. The area reflected the rate at which ocular vergence returned to the original phoria position. The mean area for the monocular condition was 300.9, the mean area for alternate fixation with no binocular time was 300.3, and the mean area for alternate fixation with binocular time was 205.2. CONCLUSIONS: Saccadic alternations do not affect phoria adaptation. However, short periods in which binocular disparate images are viewed significantly increase the rate at which phoria adaptation declines for some subjects.

Adaptation, Ocular↗

PubMed1992

Quantitative analysis of associated and disassociated phorias: linear and nonlinear static models.

Ogle proposed two measures of oculomotor balance, called associated and disassociated phorias, which he assumed were equivalent. However, experimentally determined values of these phorias do not show a close correspondence. To analyze the rationale behind Ogle's assumption of equality, a linear static model was evaluated. It was found that indeed the linear model predicts an exact correspondence between associated and disassociated phorias. Thus, his assumption depended on the presence of a linear model. To account for the discrepancy between these two measures, a nonlinear static model, containing the dead space operators depth of field and Panum's fusional area, was evaluated. Four equations for fixation disparity were derived corresponding to the four combinations of deadspace operator outputs. It was found that only one of these four equally possible solutions for associated phoria corresponded to the disassociated phoria. This suggests that the variability in the four solutions may account for the scatter in the experimental data. The nonlinear model was analyzed further to determine its sensitivity to parameter changes and to show how such a model could generate the classical shape of the fixation disparity curve.

Accommodation, Ocular↗

PubMed1988

Comparisons of commercially available devices for the measurement of fixation disparity and associated phorias.

Associated phorias were measured on 89 subjects using various commercially available devices to compare the results obtained with them. An additional 14 persons served as subjects to compare fixation disparity curve parameters obtained with two different targets. Distance associated phorias using the Mallett unit and the American Optical vectographic slide were not significantly different. Nearpoint associated phorias using the Bernell unit and the Borish card were not significantly different. Associated phorias obtained with the Bernell unit and the Borish card were lower in magnitude than the associated phorias (x-intercepts) from fixation disparity curves derived using the Sheedy disparometer. Fixation disparity curve parameters using the Wesson fixation disparity card differ from those obtained with the Sheedy disparometer. Subjective comments on the clinical use of each of these instruments are included.

Adult↗

PubMed1983

Phoria adaptation to prisms. A cerebellar-dependent response.

Horizontal prism placement in normal subjects results in an apparent change in phoria by an amount equal in power and opposite in direction to the prisms used. However, the measured phoria gradually returns toward the value preceding the placement of prisms. This is termed phoria adaptation. This response was measured in five normal subjects and five patients with cerebellar deficit. The magnitude of the response was significantly reduced in the patient group. Visual acuities and fusional reserves were comparable in the two groups. The mean age was greater, and the stereoscopic acuity decreased, in the patient group. These factors were unlikely to account for the reduced response in patients. The results suggest that the phoria adaptation response in normal subjects depend on the integrity of the cerebellum.

Adaptation, Physiological↗

PubMed1993

Spatial aspects of vertical phoria adaptation.

Vergence adaptation to vertical disparity spreads to unadapted directions of gaze. The spatial spread function for prism adaptation was estimated from aftereffects of a vertical disparity presented at a single position. Constraints limiting the spatial spread of adaptation were investigated with two stimuli of opposite disparity (hyper and hypo), presented at two different eye positions with a separation that varied from 6 to 18 deg in either the horizontal or vertical meridian. On average, phoria adaptation to the single point paradigm spread uniformly across the entire 18 deg test field. A resolution limit for adaptation to the two point paradigm was demonstrated by a reduction of phoria aftereffects with decreasing target separation (crowding). Vertical phoria aftereffects were reduced more by horizontal than by vertical crowding. A disparity gradient limit was demonstrated for a fixed target separation by a reduction of gain (phoria change/stimulus disparity) with increasing stimulus disparity.

Adaptation, Ocular↗

PubMed1978

Apparent movement, eye movements and phoria when two eyes alternate in viewing a stimulus.

Three experiments were conducted to test the hypothesis that the apparent movement of a stimulus when the two eyes are alternately occluded can be explained by phoria and Hering's principles of visual direction. In experiments 1 and 2, the direction of apparent movement, eye position, and eye movements were measured when eye movements did and did not occur. In experiment 3, the magnitude of apparent movement and the extent of phoria were comapred. Results from the experiments 1 and 2 indicated that the direction of apparent movement could be predicted from the direction of phoria, in conjunction with Hering's principles, and was not contingent on eye movements. In experiment 3, a high positive correlation (r = 0.95) between the magnitude of apparent movement and the extent of phoria was obtained.

Eye Movements↗

PubMed1982

Phoria measurements using chromatic targets.

Von Graefe phoria measurements were obtained for ten prepresbyopic subjects at 40 cm and 6 m test distances using a vertical column of black letters on red, green, and white backgrounds. Phorias measured at 40 cm using red and white target backgrounds were similar, but the phoria measured using a green target background indicated a change toward greater exophoria. No difference in phoria measurements was found between all targets at 6 m.

Accommodation, Ocular↗