The Effect of Illumination and Foveal Fusion Lock on Clinical Fixation Disparity Measurements With the Sheedy Disparometer

Wildsoet, Christine F.; Cameron, Kel D.

doi:10.1111/j.1475-1313.1985.tb00653.x

Cited by 29 publications

(16 citation statements)

References 16 publications

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“…These results are consistent with the results of Yekta et al (1989) that amount of divergent y-intercept and base-in x-intercept increases with the lack of foveal lock. Also, our results are in concordance with findings of Brautaset & Jennings (2006), Wildsoet & Cameron (1985) and Debysingh et al (1986), who reported that FDC parameters with devices that have a foveal lock are more stable, and the x-intercept has a lower range. According to our findings, the standard deviation of the y-intercept and the x-intercept with the Wesson FD card were higher than the modified Mallett unit.…”

Section: Discussionsupporting

confidence: 95%

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Evaluation of Fixation Disparity Curve with the Modified Near Mallett Unit and the Wesson Fixation Disparity Card in Symptomatic and Asymptomatic Subjects

et al. 2012

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Among symptomatic participants in this study, both Type I and Type III FD are more common than previously thought, but depend upon the method used to measure it. The x-intercepts were on average displaced in the base-in direction, y-intercepts were shifted in the exo direction, and the slopes were steeper with the Wesson FD card compared with the modified near Mallett unit. This may be related to the design of two devices. These differences were more significant in the symptomatic group.

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Section: Discussionsupporting

confidence: 95%

“…In the studies of Ogle et al (1976), Sheedy & Saladin (1978), Wick (1985), Wildsoet & Cameron (1985), and Yekta et al (1989), the most prevalent curve type was type I, which is similar to our results.…”

Section: Strabismussupporting

confidence: 94%

Evaluation of Fixation Disparity Curve with the Modified Near Mallett Unit and the Wesson Fixation Disparity Card in Symptomatic and Asymptomatic Subjects

et al. 2012

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“…In the studies of Ogle et al(13) Sheedy and Saladin, (7) Wick (8), Wildsoet and Cameron (28) and Yekta et al(17) the most prevalent curve type was type I, which is similar to our results. The previous studies reported that curve type is an important indicator of decompensated heterophoria, (7, 13) with curve type I as a normal curve and other curve types being more common in symptomatic subjects.…”

Section: Discussionsupporting

confidence: 91%

Evaluation of Fixation Disparity Curve Parameters With the Modified Near Mallett Unit in Symptomatic and Asymptomatic University Students

Moghadam¹,

Goss²,

Yekta³

et al. 2013

Iran Red Cres Med J

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BackgroundResearch suggests that fixation disparity data are extremely useful in the assessment of the binocular and accommodative systems.ObjectivesThe purpose of this study was to evaluate fixation disparity curve (FDC) parameters with a modified near Mallett unit in symptomatic and asymptomatic students of Paramedical Sciences School of Mashhad University of Medical Sciences in 2007.Patients and MethodsIn this analytical-descriptive study, 100 students were selected randomly and divided into symptomatic and asymptomatic groups. Fixation disparity curve parameters were determined for each subject and compared in symptomatic and asymptomatic groups.ResultsThere were more subjects with exo fixation disparity than eso fixation disparity in the study sample. The means for fixation disparity, fixation disparity curve x-intercept, and slope with the modified Mallett unit were each significantly different by Mann-Whitney U test in the symptomatic and asymptomatic groups. Also there was a significant difference in the distributions of fixation disparity curve types in the two symptom groups by Chi-square test.ConclusionsThe X-intercepts (point at which the FDC crosses the X-axis) were on average more in the base-in direction, Y-intercepts (point at which the FDC crosses the Y-axis) were shifted in the exo direction, and slopes were steeper in the symptomatic group.

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“…, 1949). The lack of a central fusion lock destabilises (Wildsoet and Cameron, 1985) and increases (Brownlee and Goss, 1988) fixation disparity and under these unnatural conditions fixation disparity is therefore a less useful indicator of visual stress (Evans, 2002).…”

Section: Introductionmentioning

confidence: 99%

The Mallett Fixation Disparity Test: influence of test instructions and relationship with symptoms

Karania

Evans

2006

Ophthalmic Physiologic Optic

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Fixation disparity is a minute ocular misalignment under conditions of binocular single vision and is typically detected in primary eye care practices in the UK using the Mallett Unit Fixation Disparity Test. This instrument creates natural viewing conditions, when the patient's binocular system is fused using both central and peripheral fusion locks. This allows the examiner to determine the minimum prism power that eliminates the fixation disparity: the associated phoria or aligning prism. The spherical power that eliminates the fixation disparity, the aligning sphere, can also be determined. The near Mallett Unit Fixation Disparity Test has been shown to have good sensitivity and specificity for detecting symptomatic heterophoria. Cases of decompensated heterophoria tend to have a fixation disparity and the aligning prism or aligning sphere is a good indicator of the correction that will render the heterophoria compensated. The purpose of this study was, for the first time, to investigate the effect of test instructions on the results of the Mallett Unit Fixation Disparity Test. In study 1, we surveyed and observed practitioners to determine the instructions that are typically used. In study 2, we compared results obtained with this ÔstandardÕ method of questioning with a more ÔspecificÕ form of questioning that has been suggested in the literature. The participants for study 2 were 105 patients aged 7-70 years who were randomly selected from those attending a community optometric practice. Significantly different results were obtained with the two sets of instructions. The specific form of questioning revealed more cases of fixation disparity and the results with this method showed a better correlation with symptoms. This only held for near vision: for distance vision, symptoms were not significantly correlated with the presence of fixation disparity. This agrees with previous work with the Mallett unit, which showed a significant relationship with symptoms only at near. We also found that patients with more severe symptoms had greater degrees of aligning prism. Our study supports previous work indicating that the Mallett unit is a useful tool for detecting symptomatic heterophoria at near. However, we found that the testing method is important: patients need to be asked not just whether the nonius strips are aligned but also whether one or both of the strips ever moves. More research is needed to investigate the significance of precise test instructions in other optometric and orthoptic tests.

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The Effect of Illumination and Foveal Fusion Lock on Clinical Fixation Disparity Measurements With the Sheedy Disparometer

Cited by 29 publications

References 16 publications

Evaluation of Fixation Disparity Curve with the Modified Near Mallett Unit and the Wesson Fixation Disparity Card in Symptomatic and Asymptomatic Subjects

Evaluation of Fixation Disparity Curve with the Modified Near Mallett Unit and the Wesson Fixation Disparity Card in Symptomatic and Asymptomatic Subjects

Evaluation of Fixation Disparity Curve Parameters With the Modified Near Mallett Unit in Symptomatic and Asymptomatic University Students

The Mallett Fixation Disparity Test: influence of test instructions and relationship with symptoms

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