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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↗

PubMed1999

Relationship of accommodative response and nearpoint phoria in a sample of myopic children.

Esophoria has been associated with onset and progression of myopia in children. The induction of myopia by optical defocus shown by animal models suggests that a high lag of accommodation during near work may contribute to myopia in children. This paper examines the relationship of nearpoint phoria and accommodative response in a sample of children with myopia. Accommodative response was measured under binocular conditions with the Canon Autoref R-1 autorefractor with a 40 cm viewing distance. Phorias were measured with the von Graefe method using a 40 cm test distance. In the statistical analysis exophoria was scored as a negative number and esophoria was scored as a positive number. The coefficient of correlation of accommodative response with phoria was -0.32 (n = 73; p<0.01), thus showing an association of a more positive (more convergent) near phoria with lower accommodative response. The correlation coefficient increased to -0.39 when an exponential function was used. When only esophores were considered, the correlation coefficient was -0.59 (n = 44; p<0.001). Lower accommodative response (higher lag of accommodation) was associated with greater esophoria.

Accommodation, Ocular↗

PubMed2000

Surgical modification of the AC/A ratio and the binocular alignment ("Phoria") at distance; its influence on accommodative esotropia: a study of 21 cases.

PURPOSE: To study these changes in patients and their relation to manifestation of accommodative esotropia and response to surgery. METHODS: Patient-subjects: 21 patients who had difficulty adjusting to spectacle correction and underwent bilateral medial rectus loop suspension-recession surgery to alleviate their accommodative esotropia. Measurements of AC/A, uncorrected distance phoria, and related parameters were taken before and after surgical intervention was performed and were analyzed using analysis of variance (ANOVA). RESULTS: Both AC/A ratios and the distance phorias are "statistically significantly" (p< or =0.05), and independently, reduced by this surgical procedure. The manifestation of accommodative esotropia and response to surgery can be fairly accurately predicted from the values of AC/A ratio and distance phoria. CONCLUSION: Surgical treatment of accommodative esotropia creates well defined, long-lasting reductions in the AC/A ratio and the distance phoria.

Accommodation, Ocular↗

PubMed2002

Impaired vertical phoria adaptation in patients with cerebellar dysfunction.

PURPOSE: To determine whether phoria adaptation to a vertical prism disparity is altered in patients with cerebellar dysfunction. METHODS: With a computer-aided haploscope, adaptive responses of fusion-free eye position to a 10- or 30-minute period was measured in subjects wearing a 3-prism diopter vertical prism over one eye. Thirteen patients with well-documented cerebellar diseases who did not have manifest ocular misalignment or limited versional eye movement and age-matched healthy subjects participated. RESULTS: The mean +/- SD percentage of vertical phoria adaptation was 13% +/- 22% and 20% +/- 16% for the 10- and 30-minute adaptations, respectively. These levels were significantly smaller than the respective ones in the age-matched control group (P < 0.001, repeated measures MANOVA). Seven (54%) of 13 patients, including two with genetically confirmed pure cerebellar lesions (spinocerebellar ataxia type 6), showed markedly reduced responses to both the 10- and 30-minute adaptations. In all three patients with acute cerebellar ataxia, the adaptive response was improved at the same time as remission of cerebellum-associated neurologic deficits. CONCLUSIONS: Phoria adaptation to vertical binocular disparity is frequently impaired in patients with cerebellar dysfunction. These results bolster the hypothesis that phoria adaptation is a cerebellar-dependent response.

Adaptation, Ocular↗

PubMed2003

Comparison of the time courses of concomitant and nonconcomitant vertical phoria adaptation.

Vertical phoria adaptation was measured before, during, and after 1 h of training with either a prism or magnifying lens. With the prism (concomitant adaptation) a single vertical disparity was presented at primary position. With the magnifier (nonconcomitant adaptation) two vertical disparities of opposite sign were presented along the vertical meridian. Following adaptation, binocular vision was prevented with an eye patch, and vertical phorias were measured periodically along the primary vertical meridian over the course of 8 h. Despite individual variation, adaptation followed approximately exponential time courses. The average time constants for the decay of concomitant and nonconcomitant adaptation were 31 and 83 min, respectively. There was no consistent relationship between the rates of acquisition and decay nor was there a strong relationship between the gains of the adaptive responses and the rates of decay although there was a general trend for the gains of the nonconcomitant responses to be higher and the rate of decay slower than the concomitant responses. The results support the notion that concomitant and nonconcomitant phoria adaptation involve different mechanisms but not the contention that adaptation to prisms is easier or more robust than adaptation to lenses.

Adaptation, Physiological↗

PubMed1987

Effect of head and eye positions on fixation disparities, phorias, and ductions at near.

This study evaluated the effects of head and gaze position on near fixation disparity, phoria, and duction findings. A population of 104 non-complaining subjects divided by age into 3 groups participated in the study. The primary head and gaze position along with two others approximating the positions used for reading by nonbifocal and bifocal wearers were used. A statistically significant effect was found for the phoria data from the young group, but the magnitude was clinically insignificant. Changes in head and/or gaze positions did not significantly affect fixation disparities or duction recovery ranges. Phorias and fixation disparities showed statistically significant increases in exo deviation with increasing age regardless of head and/or gaze position. Nine of 23 presbyopic subjects gave erratic findings during fixation disparity testing and this casts doubt upon the clinical usefulness of this procedure with presbyopes.

Adolescent↗

PubMed2000

Associated phoria in relation to stereopsis with random-dot stereograms.

In the present work, we use random-dot stereograms to test a possible relationship between associated phoria and stereopsis. We determined, using a modified constant-stimulus method, the disparity range that indicates the maximum range at which stereoscopic correspondence can be achieved. A total of 27 observers took part in the experiment. The value of the disparity range as a function of the associated phoria (measured with a Mallet unit) seems to indicate that greater associated phoria (fixation disparity) correlates with a deterioration in stereoscopic vision, reducing the disparity range and therefore the space region in which stereoscopic vision can be attained.

Adult↗

PubMedDate not supplied

Recovery of phorias following monocular occlusion.

Fourteen nonstrabismic volunteers were monocularly patched for 2 and 24 hours in separate experiments. Horizontal and vertical phorias were measured at 6 m and 30 cm, at 30-second intervals, for at least 30 minutes, following removal of the patch. After 24 hours of monocular occlusion, the initial change from baseline at 6 m ranged from 9.5 prism diopters exo to 7 delta eso and 6.5 delta hyper to 3 delta hypo. At 30 cm, the initial change ranged from 7.5 delta exo to 4 delta eso and 1 delta hyper to 1 delta hypo. In all but three subjects, phorias returned to within 2 delta of baseline by 3 minutes, and in all subjects by 25 minutes. After 2 hours of monocular occlusion, the range of initial change from baseline was similar to 24 hours of occlusion, but all phorias returned to within 2 delta of baseline by 2.5 minutes. Therefore, we suggest that ocular alignment should not be routinely measured within 3 minutes of removing a patch. If patched for 24 hours, a few individuals will require up to 25 minutes for stabilization of their deviation. Further studies might address these effects in patients with subnormal fusion and stereopsis.

Adult↗

PubMed1991

Variation and correlation of standard clinical phoropter tests of phorias, vergence ranges, and relative accommodation in a sample of school-age children.

This paper presents a study of standard clinical phoropter tests of dissociated phorias, fusional vergence ranges, and relative accommodation ranges in 244 school-age (7.9 to 15.9 years of age) children. The tests studied included von Graefe phorias and base-in and base-out fusional vergence ranges at both distance and near, as well as negative relative accommodation (NRA) and positive relative accommodation (PRA) tests. Coefficients of correlation among the various tests are presented. Means and correlations were similar to those previously reported for adult populations. Distributions of distance lateral phorias and some distance fusional vergence parameters were leptokurtic.

Accommodation, Ocular↗

PubMed1978

Aftereffects of sustained vertical divergence: induced vertical phoria and illusory target height.

Maintaining vertical divergence of about 2 diopters for 6, 8, or 10 min was shown to yield an induced vertical phoria (IVP). IVP increased with the duration of the inducing period and decayed with time in the dark, though not completely. Decay of IVP decreased with duration of induction period and increased as a result of maintaining the normal fusional response for 30 s. Vertical eye movements in the dark, however, were ineffective in reducing IVP. Some evidence also was provided for eye-specific errors in the perception of elevation of a visible target that were appropriate to the direction of the induced phoria. It was proposed that IVP may be modulated by resetting the output of the system used to induce the original effect.

Darkness↗

PubMed2001

Associated phoria and the measuring and correcting methodology after H.-J. Haase (MKH).

The test charts included in the Polatest, designed by H.-J. Haase and manufactured by Zeiss, are used in Germany, Switzerland and Scandinavia for prism correction of 'associated phoria.' From clinical experience with the Polatest Haase developed a motor and sensory theory of the different stages of decompensation of 'associated phoria ' and a strategy for its prismatic correction - the MKH (Measuring and Correcting Methodology after H.-J. Haase). The theory challenges many accepted ideas about the plasticity of the visual system and the use of prisms in the treatment of sensory abnormalities. This article, the first full description in English, describes and critically discusses the MKH.

Accommodation, Ocular↗

PubMed1984

Effect of monocular occlusion on lateral phoria.

Several experiments have shown that monocular occlusion (MO) leads to a variety of changes in the visual functioning of the non-occluded eye. An experiment was conducted to assess the effect of 24 hr of MO on the lateral phoria, a binocular phenomenon. The results demonstrated marked tendencies for increased esophoria after MO, especially for near vision. Follow-up tests revealed that normal phoria was re-established 24 hr after the termination of MO. The results are discussed in the context of the use of MO in treatment procedures for visual dysfunctions and their implication for future investigations.

Accommodation, Ocular↗

PubMed1996

How good is the estimated cover test at predicting the von Graefe phoria measurement?

Results obtained on the estimated cover test and the von Graefe phoria measurement were compared in order to determine how well the former test predicted the result of the latter. Subjects for the study were 25 clinic patients and 28 optometry students. Examiners were two fourth-year optometry interns. For testing at 6 m, correlations between the estimated cover test and the von Graefe measurement were relatively high, although for some subjects the cover test underestimated the von Graefe measurement by as much as 4 delta of exophoria and 6 delta of esophoria. For testing at 40 cm, correlation coefficients were somewhat lower, and the cover test underestimated the von Graefe measurement by as much as 11 delta of exophoria and 13 delta of esophoria. It was concluded that although the estimated cover test is valuable as a screening test, it should be followed by prism neutralization or by von Graefe phoria measurement.

Adult↗

PubMed2003

The symptomatic patient with normal phorias at distance and near: what tests detect a binocular vision problem?

PURPOSE: Patients often manifest symptoms that appear to be related to binocular distress. Many of these patients have normal heterophoria at distance and near, making the etiology of such symptoms perplexing. We performed a visual examination of patients having normal heterophoria at distance and near in order to investigate which visual analysis tests differentiate symptomatic from asymptomatic patients. METHODS: Eighty subjects (30 symptomatic, 50 asymptomatic) with ages between 18 to 35 years of either sex and any race were pooled based on vision-symptom level determined by a 9-question standardized visual-symptoms questionnaire scored using a 100-point scale (asymptomatic: score > or = 85; symptomatic: score < or = 75). Inclusion/exclusion criteria included vision correctable to 6/6 (20/20) Snellen acuity or better in each eye, normal phorias, no latent cyclovertical heterophoria, and normal ocular health. RESULTS: Of the 30 symptomatic patients, 18 had reduced vergence facility response using 3 pd base-in/12 pd base-out loose prism at distance (n = 10; t-score = 2.41, p < 0.02, d = 76) and near (n = 15; t-score = 3.32, p < 0.01, df = 78) with a significant difference beyond the 0.02 level. No other test including measurement of accommodation, showed a significant between-group difference. However, three patients with normal vergence facility (distance and near) showed a reduced binocular accommodative facility response (+/-2.00 D at 40 cm). CONCLUSION: Given a patent with asthenopia, normal phorias, and visual acuity, a differential diagnosis may be made based primarily on using vergence facility and accommodative facility testing. From a clinical standpoint, the results expedite diagnosis of binocular vision abnormalities and direct treatment.

Accommodation, Ocular↗

PubMed1991

Linear model of accommodation and vergence can account for discrepancies between AC/A measures using the fixation disparity and phoria methods.

The AC/A ratios obtained previously by the fixation disparity method were in most cases greater than those by the phoria method. An earlier study analysed a simplified linear model of the accommodation and vergence system. It was determined that the equations corresponding to the two methods were equal, indicating that such a model could not account for the discrepancy found experimentally. However, two important components--tonic accommodation and tonic vergence--were omitted from this simplified model. In the present study, an analysis of the complete linear model showed that the equations corresponding to the two methods are different. In addition, calculation of the error between the cross-link gain and the overall accommodative input--convergence output values indicated that the AC/A should be higher using the fixation disparity than the phoria method. Therefore, the predictions of the complete linear model are consistent with the data obtained experimentally.

Accommodation, Ocular↗

PubMed1990

Phoria adaptation in patients with cerebellar dysfunction.

The authors studied phoria adaptation to horizontal base-out prism in 17 patients with well-documented cerebellar lesions. There was no significant difference between mean adaptation measured in the patients and ten normal controls. Individually, normal adaptation was found in 12 patients. Abnormal adaptation was found in five patients, all but one of which had other neurologic lesions. These results suggest that phoria adaptation to base-out prism is not diminished by a cerebellar lesion unless it is accompanied by another nervous system lesion(s).

Adaptation, Ocular↗

PubMed2002

Vertical memory-based disconjugate learning for downward saccades at a viewing distance of 70 cm: relation to horizontal vergence and to vertical phoria.

The goal of this study was to examine vertical disconjugate learning based on memorization of vertical disparity at a viewing distance of 70 cm; such a distance is common in many visual ergonomic conditions, including car driving. For a period of 15 min, eight subjects made downward saccades to a memorized target. The target was rendered disparate with the use of a magnifier placed in front of one eye. Learning occurred in only four of the subjects: saccades became disconjugate and the disconjugacy was retained when the target was not disparate. These observations extend a prior study dealing with a longer distance (1 m) and indicate that such learning is subject dependent for both viewing distances. Importantly, the present study shows, for the first time, that vertical disconjugate learning is related to two other phenomena: (a) the horizontal vergence present during vertical saccades and (b) the degree of vertical phoria normal subjects exhibit.

Adolescent↗