The fixation target influences the near deviation and AC/A ratio in intermittent exotropia

Le, Thong; Koklanis, Konstandina; Georgievski, Zoran

doi:10.1016/j.jaapos.2009.11.014

Cited by 15 publications

(8 citation statements)

References 18 publications

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“…We found that classifying our participants into conventional clinical groupings was difficult and of limited value: one case would show a larger increase for near with occlusion, another would increase more for distance and another equally for both distances; some angles would change as much with occlusion as with lenses, while others changed very little; plus lenses could produce great changes in angle, while minus lenses would produce very little in the same child. We found that responses to occlusion, lenses and near versus distance fixation fell along a continuum, as also found by Le et al. (2010).…”

Section: Discussionsupporting

confidence: 84%

Evidence that convergence rather than accommodation controls intermittent distance exotropia

Horwood

Riddell

2012

Acta Ophthalmologica

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. Purpose: This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. Methods: Nineteen distance exotropes, aged 4–11 years, were compared while controlling their deviation with 27 non‐exotropic controls aged 5–9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2 m and 33 cm. Stimulus and response AC/A and CA/C ratios were calculated. Results: Accommodation responses for near targets (p = 0.017) and response gains (p = 0.026) were greater in the exotropes than in the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p = 0.02), but significantly higher CA/C ratios (p = 0.02). All the exotropes, whether the angle changed most with lenses (‘controlled by accommodation’) or on occlusion (‘controlled by fusion’), used binocular disparity not blur as their main cue to target distance. Conclusions: Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting overaccommodation driven by controlling convergence, rather than by inducing blur‐driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios.

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Section: Discussionsupporting

confidence: 84%

Evidence that convergence rather than accommodation controls intermittent distance exotropia

Horwood

Riddell

2012

Acta Ophthalmologica

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“…The AC/A ratio relies on a theoretical causal link between accommodation and vergence 73 , 77 – 83 , which our results make tenuous. Thus using the AC/A ratio to help determine the appropriate surgical or optical interventions for strabismus may contribute to their often unpredictable outcomes 55 , 78 , 83 – 94 . Furthermore, our results suggest there may be subtypes of strabismus that arise from primary vergence or accommodation disorders.…”

Section: Discussionmentioning

confidence: 99%

A covered eye fails to follow an object moving in depth

Chandna

Badler

Singh

et al. 2021

Sci Rep

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To clearly view approaching objects, the eyes rotate inward (vergence), and the intraocular lenses focus (accommodation). Current ocular control models assume both eyes are driven by unitary vergence and unitary accommodation commands that causally interact. The models typically describe discrete gaze shifts to non-accommodative targets performed under laboratory conditions. We probe these unitary signals using a physical stimulus moving in depth on the midline while recording vergence and accommodation simultaneously from both eyes in normal observers. Using monocular viewing, retinal disparity is removed, leaving only monocular cues for interpreting the object’s motion in depth. The viewing eye always followed the target’s motion. However, the occluded eye did not follow the target, and surprisingly, rotated out of phase with it. In contrast, accommodation in both eyes was synchronized with the target under monocular viewing. The results challenge existing unitary vergence command theories, and causal accommodation-vergence linkage.

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“…Over 75% of patient have increase in near deviation after patch test and decrease in calculated AC/A ratio. 13 By using standard methods, Cooper and Coworkers calculated AC/A in patients of intermittent exotropia. Patient first underwent a monocular occlusion of one hour for measurement of actual near deviation.…”

Section: Discussionmentioning

confidence: 99%

Comparison of AC/A Ratio in True and Simulated Divergence Excess Exotropia

Sagheer¹,

Haider²,

Bukhari³

et al. 2021

pak J Ophthalmol

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Purpose: To compare the accommodation convergence per accommodation ratio (AC/A) in true and simulated divergence excess exotropia. Study Design: Comparative cross sectional study. Place and Duration of Study: Department of ophthalmology, Punjab Rangers teaching hospital, Lahore, from July 2019 to December 2019. Methods: The study included 20 patients each of intermittent exotropia (XT) true and simulated divergence excess exotropia (XT).All the subjects underwent complete orthoptic assessmentthat included AC/A ratio calculation through heterophoria method after monocular occlusion. Results: The Results showed that patients with true divergence excess exotropia have a high AC/A ratio as compared to patients with simulated divergence excess exotropia who have a normal AC/A ratio. 57% patients showed true divergence excess exotropia with high AC/A ratio while 43% had divergence excess with normal AC/A ratio. Conclusion: The response of AC/A was found to be higher in patients with true divergence excess exotropia after monocular occlusion. Key Words: Intermittent exotropia, True simulated divergence excess exotropia, simulated divergence excess exotropia.

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The fixation target influences the near deviation and AC/A ratio in intermittent exotropia

Cited by 15 publications

References 18 publications

Evidence that convergence rather than accommodation controls intermittent distance exotropia

Evidence that convergence rather than accommodation controls intermittent distance exotropia

A covered eye fails to follow an object moving in depth

Comparison of AC/A Ratio in True and Simulated Divergence Excess Exotropia

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