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Sustained fixation induced changes in phoria and convergence peak velocity.

Kim EH, Vicci VR, Han SJ, Alvarez TL - PLoS ONE (2011)

Bottom Line: A repeated measures ANOVA showed that convergence far steps were significantly faster than the near steps (p<0.03).A weaker correlation was observed for the near convergence steps (r = 0.59, p = 0.20).Future investigations should include a systematic study of how prisms may influence convergence and divergence eye movements for those prescribed with prisms within their spectacles.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, New Jersey Institute of Technology, Newark, New Jersey, United States of America.

ABSTRACT

Purpose: This study sought to investigate the influence of phoria adaptation on convergence peak velocity from responses located at different initial vergence positions.

Methods: Symmetrical 4° convergence step responses and near dissociated phoria (measured at 40 cm from the subject's midline) were recorded from six subjects with normal binocular vision using an infrared limbus tracking system with a haploscope. Two different sustained fixations (1° and 16° convergent rotation along the subject's midline) were used to study whether phoria had an influence on the peak velocity of convergence responses located at two initial vergence positions (1° or 'far' steps and 12° or 'near' steps).

Results: Phoria was significantly adapted after a sustained fixation task at near (16°) and far (1°) (p<0.002). A repeated measures ANOVA showed that convergence far steps were significantly faster than the near steps (p<0.03). When comparing convergence steps with the same initial vergence position, steps measured after near phoria adaptation were faster than responses after far adaptation (p<0.02). A regression analysis demonstrated that the change in phoria and the change in convergence peak velocity were significantly correlated for the far convergence steps (r = 0.97, p = 0.001). A weaker correlation was observed for the near convergence steps (r = 0.59, p = 0.20).

Conclusion: As a result of sustained fixation, phoria was adapted and the peak velocity of the near and far convergence steps was modified. This study has clinical considerations since prisms, which evoke phoria adaptation, can be prescribed to help alleviate visual discomfort. Future investigations should include a systematic study of how prisms may influence convergence and divergence eye movements for those prescribed with prisms within their spectacles.

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Related in: MedlinePlus

Summary per subject of baseline phoria before 16° sustained fixation (dark gray bar), baseline phoria before 1° sustained fixation experiment (light gray bar), adapted phoria after 16° sustained fixation task (medium gray bar) and adapted phoria after 1° sustained fixation task (white bar) for all six subjects.Adapted phoria measurements are the average of phoria measurements after the three minutes of sustained convergence, after near steps with an initial vergence position of 12° and after far steps with an initial vergence position of 1°. The error bars are one standard deviation from the mean.
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pone-0020883-g004: Summary per subject of baseline phoria before 16° sustained fixation (dark gray bar), baseline phoria before 1° sustained fixation experiment (light gray bar), adapted phoria after 16° sustained fixation task (medium gray bar) and adapted phoria after 1° sustained fixation task (white bar) for all six subjects.Adapted phoria measurements are the average of phoria measurements after the three minutes of sustained convergence, after near steps with an initial vergence position of 12° and after far steps with an initial vergence position of 1°. The error bars are one standard deviation from the mean.

Mentions: The sustained fixation tasks altered the phoria level depending on the vergence position. A summary of the phoria measurements of all six subjects is shown in figure 4. All subjects became significantly more esophoric after the 16° sustained convergence task (p = 0.002). Similarly, after the far convergence task (1° vergence fixation), all six subjects became significantly more exophoric (p = 0.0008). The baseline phoria measurements were not significantly different between the two days of recording (p = 0.65).


Sustained fixation induced changes in phoria and convergence peak velocity.

Kim EH, Vicci VR, Han SJ, Alvarez TL - PLoS ONE (2011)

Summary per subject of baseline phoria before 16° sustained fixation (dark gray bar), baseline phoria before 1° sustained fixation experiment (light gray bar), adapted phoria after 16° sustained fixation task (medium gray bar) and adapted phoria after 1° sustained fixation task (white bar) for all six subjects.Adapted phoria measurements are the average of phoria measurements after the three minutes of sustained convergence, after near steps with an initial vergence position of 12° and after far steps with an initial vergence position of 1°. The error bars are one standard deviation from the mean.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3117850&req=5

pone-0020883-g004: Summary per subject of baseline phoria before 16° sustained fixation (dark gray bar), baseline phoria before 1° sustained fixation experiment (light gray bar), adapted phoria after 16° sustained fixation task (medium gray bar) and adapted phoria after 1° sustained fixation task (white bar) for all six subjects.Adapted phoria measurements are the average of phoria measurements after the three minutes of sustained convergence, after near steps with an initial vergence position of 12° and after far steps with an initial vergence position of 1°. The error bars are one standard deviation from the mean.
Mentions: The sustained fixation tasks altered the phoria level depending on the vergence position. A summary of the phoria measurements of all six subjects is shown in figure 4. All subjects became significantly more esophoric after the 16° sustained convergence task (p = 0.002). Similarly, after the far convergence task (1° vergence fixation), all six subjects became significantly more exophoric (p = 0.0008). The baseline phoria measurements were not significantly different between the two days of recording (p = 0.65).

Bottom Line: A repeated measures ANOVA showed that convergence far steps were significantly faster than the near steps (p<0.03).A weaker correlation was observed for the near convergence steps (r = 0.59, p = 0.20).Future investigations should include a systematic study of how prisms may influence convergence and divergence eye movements for those prescribed with prisms within their spectacles.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, New Jersey Institute of Technology, Newark, New Jersey, United States of America.

ABSTRACT

Purpose: This study sought to investigate the influence of phoria adaptation on convergence peak velocity from responses located at different initial vergence positions.

Methods: Symmetrical 4° convergence step responses and near dissociated phoria (measured at 40 cm from the subject's midline) were recorded from six subjects with normal binocular vision using an infrared limbus tracking system with a haploscope. Two different sustained fixations (1° and 16° convergent rotation along the subject's midline) were used to study whether phoria had an influence on the peak velocity of convergence responses located at two initial vergence positions (1° or 'far' steps and 12° or 'near' steps).

Results: Phoria was significantly adapted after a sustained fixation task at near (16°) and far (1°) (p<0.002). A repeated measures ANOVA showed that convergence far steps were significantly faster than the near steps (p<0.03). When comparing convergence steps with the same initial vergence position, steps measured after near phoria adaptation were faster than responses after far adaptation (p<0.02). A regression analysis demonstrated that the change in phoria and the change in convergence peak velocity were significantly correlated for the far convergence steps (r = 0.97, p = 0.001). A weaker correlation was observed for the near convergence steps (r = 0.59, p = 0.20).

Conclusion: As a result of sustained fixation, phoria was adapted and the peak velocity of the near and far convergence steps was modified. This study has clinical considerations since prisms, which evoke phoria adaptation, can be prescribed to help alleviate visual discomfort. Future investigations should include a systematic study of how prisms may influence convergence and divergence eye movements for those prescribed with prisms within their spectacles.

Show MeSH
Related in: MedlinePlus