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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 of average peak velocities (°/s) with one standard deviation of all 4° convergence step responses after near 16° sustained fixation (top) and after far 1° sustained fixation (bottom).Far step data after sustained fixation of 16° (black), near step data after sustained fixation of 16° (light gray), far step data after sustained fixation of 1° (dark gray) and near step data after sustained fixation of 1° (white) are plotted. The number of samples is reported below the plotted data. When the phoria is maintained at one position, convergence responses with a 1° initial vergence position are faster than responses with a 12° initial vergence position.
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pone-0020883-g007: Summary of average peak velocities (°/s) with one standard deviation of all 4° convergence step responses after near 16° sustained fixation (top) and after far 1° sustained fixation (bottom).Far step data after sustained fixation of 16° (black), near step data after sustained fixation of 16° (light gray), far step data after sustained fixation of 1° (dark gray) and near step data after sustained fixation of 1° (white) are plotted. The number of samples is reported below the plotted data. When the phoria is maintained at one position, convergence responses with a 1° initial vergence position are faster than responses with a 12° initial vergence position.

Mentions: Typical 4° convergence step responses from the four conditions (after sustained fixation of 16° or 1° vergence positions and convergence steps with an initial vergence position of 12° or 1°) of subjects 1 and 2 are shown in figures 5 and 6, respectively. The visual stimulus is the same, yet the dynamics of the responses varies depending on the initial vergence position and where the person was visually sustaining prior to the convergence steps (near phoria adapted compared to far phoria adapted). When the phoria was adapted to the same location, the peak convergence steps were dependent on the initial vergence position. For example, when the subject's phoria was near-adapted using the 16° sustained fixation task, the peak velocities of the far convergence steps were faster compared to the near convergence steps. Results are plotted in figure 7A. Similarly, when the subject's phoria was far-adapted using the 1° sustained fixation, the far convergence steps were faster compared to the near convergence steps as plotted in figure 7B.


Sustained fixation induced changes in phoria and convergence peak velocity.

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

Summary of average peak velocities (°/s) with one standard deviation of all 4° convergence step responses after near 16° sustained fixation (top) and after far 1° sustained fixation (bottom).Far step data after sustained fixation of 16° (black), near step data after sustained fixation of 16° (light gray), far step data after sustained fixation of 1° (dark gray) and near step data after sustained fixation of 1° (white) are plotted. The number of samples is reported below the plotted data. When the phoria is maintained at one position, convergence responses with a 1° initial vergence position are faster than responses with a 12° initial vergence position.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3117850&req=5

pone-0020883-g007: Summary of average peak velocities (°/s) with one standard deviation of all 4° convergence step responses after near 16° sustained fixation (top) and after far 1° sustained fixation (bottom).Far step data after sustained fixation of 16° (black), near step data after sustained fixation of 16° (light gray), far step data after sustained fixation of 1° (dark gray) and near step data after sustained fixation of 1° (white) are plotted. The number of samples is reported below the plotted data. When the phoria is maintained at one position, convergence responses with a 1° initial vergence position are faster than responses with a 12° initial vergence position.
Mentions: Typical 4° convergence step responses from the four conditions (after sustained fixation of 16° or 1° vergence positions and convergence steps with an initial vergence position of 12° or 1°) of subjects 1 and 2 are shown in figures 5 and 6, respectively. The visual stimulus is the same, yet the dynamics of the responses varies depending on the initial vergence position and where the person was visually sustaining prior to the convergence steps (near phoria adapted compared to far phoria adapted). When the phoria was adapted to the same location, the peak convergence steps were dependent on the initial vergence position. For example, when the subject's phoria was near-adapted using the 16° sustained fixation task, the peak velocities of the far convergence steps were faster compared to the near convergence steps. Results are plotted in figure 7A. Similarly, when the subject's phoria was far-adapted using the 1° sustained fixation, the far convergence steps were faster compared to the near convergence steps as plotted in figure 7B.

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