Horizontal and vertical prism adaptation are different mechanisms

Brautaset, Rune; Jennings, J. A. M.

doi:10.1111/j.1475-1313.2005.00276.x

Cited by 25 publications

(25 citation statements)

References 26 publications

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“…Nevertheless those patients are not known to have more difficulties with reading which is compatible with our results. The time course of phoria adaptation as measured by others suggests that phoria may be adapted over a time course of 60 min (Graf et al, 2003; Brautaset and Jennings, 2005). Since reading of a text block was achieved within 50 ± 0.3 s (mean ± SEM) we argue that reading was indeed done not only with increased vergence demand but with an actual phoria, which might have changed over time.…”

Section: Discussionmentioning

confidence: 92%

Reading performance is not affected by a prism induced increase of horizontal and vertical vergence demand

Dysli¹,

Vogel²,

Abegg³

2014

Front. Hum. Neurosci.

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Purpose: Dyslexia is the most common developmental reading disorder that affects language skills. Latent strabismus (heterophoria) has been suspected to be causally involved. Even though phoria correction in dyslexic children is commonly applied, the evidence in support of a benefit is poor. In order to provide experimental evidence on this issue, we simulated phoria in healthy readers by modifying the vergence tone required to maintain binocular alignment.Methods: Vergence tone was altered with prisms that were placed in front of one eye in 16 healthy subjects to induce exophoria, esophoria, or vertical phoria. Subjects were to read one paragraph for each condition, from which reading speed was determined. Text comprehension was tested with a forced multiple choice test. Eye movements were recorded during reading and subsequently analyzed for saccadic amplitudes, saccades per 10 letters, percentage of regressive (backward) saccades, average fixation duration, first fixation duration on a word, and gaze duration.Results: Acute change of horizontal and vertical vergence tone does neither significantly affect reading performance nor reading associated eye movements.Conclusion: Prisms in healthy subjects fail to induce a significant change of reading performance. This finding is not compatible with a role of phoria in dyslexia. Our results contrast the proposal for correcting small angle heterophorias in dyslexic children.

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Section: Discussionmentioning

confidence: 92%

Reading performance is not affected by a prism induced increase of horizontal and vertical vergence demand

Dysli¹,

Vogel²,

Abegg³

2014

Front. Hum. Neurosci.

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“…In addition, Brautaset and Jennings report phoria adaptation is reduced in CI patients where they suggest CI patients may have a generally reduced horizontal phoria adaptation mechanism [45]. However, these patients demonstrate improvements in their ability to perform phoria adaptation [46], [47] and increases in convergence peak velocity after oculomotor training [23], [48].…”

Section: Discussionmentioning

confidence: 99%

Sustained Fixation Induced Changes in Phoria and Convergence Peak Velocity

Kim

Vicci²,

Han

et al. 2011

PLoS ONE

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PurposeThis study sought to investigate the influence of phoria adaptation on convergence peak velocity from responses located at different initial vergence positions.MethodsSymmetrical 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).ResultsPhoria 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).ConclusionAs 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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“…In the literature, the reported rates of adaptation to vertical phoria vary considerably (Brautaset & Jennings, 2005; Eskridge, 1988; Henson & North, 1980; Kono et al, 1998; Ogle & Prangen, 1953; Rutstein & Eskridge, 1986; Sethi, 1986). Some studies suggest that symptomatic subjects with hyperphoria adapt less completely to vertical prism than subjects without hyperphoria (Ogle & Prangen, 1953; Rutstein & Eskridge, 1986).…”

Section: Discussionmentioning

confidence: 99%

Vertical Heterophoria and Susceptibility to Visually Induced Motion Sickness

Jackson

Bedell²

2012

Strabismus

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Motion sickness is reported to be a common symptom in patients with vertical heterophoria. The goal of this study was to assess the relationship between vertical phoria and susceptibility to motion sickness in a non-clinical sample of 43 subjects. Vertical phoria was measured with a Maddox rod after 30 s of occlusion. To evaluate susceptibility to motion sickness, subjects read text while sitting inside a rotating optokinetic drum for 10 min. Subjects rated their level of motion sickness at 1 min intervals during drum rotation and the magnitude of 13 motion-sickness symptoms after drum rotation ended. The magnitude of vertical phoria ranged from 0 to 2.13 prism diopters (pd) with a mean of 0.46 pd and correlated significantly with both the maximum rating of motion sickness during drum rotation and the summed symptom score following rotation. A vertical phoria of 0.75 pd discriminated best between subjects with low vs. high summed motion-sickness-symptom scores (p < 0.0001). Introducing a prism to artificially increase the phoria of 12 subjects with vertical phorias < 0.75 pd increased motion-sickness symptoms in only 1 subject. Prisms that reduced the phoria of subjects with vertical phorias > 0.75 pd reduced motion-sickness symptoms in 2 of the 4 subjects tested. The results confirm an association between vertical phoria and motion sickness, but suggest the relationship may not be causal.

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Horizontal and vertical prism adaptation are different mechanisms

Cited by 25 publications

References 26 publications

Reading performance is not affected by a prism induced increase of horizontal and vertical vergence demand

Reading performance is not affected by a prism induced increase of horizontal and vertical vergence demand

Sustained Fixation Induced Changes in Phoria and Convergence Peak Velocity

Vertical Heterophoria and Susceptibility to Visually Induced Motion Sickness

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