Incomitance and Eye Dominance in Intermittent Exotropia

Adams, Daniel L.; Economides, John R.; Horton, Jonathan C.

doi:10.1167/iovs.17-22155

Cited by 18 publications

(15 citation statements)

References 41 publications

(46 reference statements)

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“…Overlap in the 95% CIs indicates that the left exotropia was not significantly different from the right exotropia, as in most patients with intermittent exotropia. 22 While this patient was viewing the central target with both eyes, he experienced eight episodes of spontaneous left exotropia. These episodes of spontaneous exotropia were similar to those induced by shutter occlusion (compare the light and dark blue traces in Fig.…”

Section: Resultsmentioning

confidence: 99%

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Bilateral Occlusion Reduces the Ocular Deviation in Intermittent Exotropia

Economides

Adams

Horton

2021

Invest. Ophthalmol. Vis. Sci.

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PURPOSE.The most common form of strabismus, intermittent exotropia, is thought to become manifest when the drive to fuse is overcome by excessive divergent muscle tone. This principle is tested by examining the alignment of the eyes in the absence of vision. We compare the ocular deviation in patients with intermittent exotropia under conditions of monocular versus binocular occlusion.METHODS. This prospective study of a patient cohort referred to our laboratory enrolled 18 patients with typical findings of well-controlled intermittent exotropia. Eye positions were recorded with video eye trackers while patients looked at a fixation spot at a distance of 57 cm. One eye was occluded, and the resulting ocular deviation was measured. Both eyes were then occluded, and the ocular deviation was re-measured. RESULTS.The majority of patients (11/18) had a smaller deviation when both eyes were covered. Occlusion of one eye resulted in a mean exotropia of 13.5°± 4.7°. Occlusion of both eyes reduced the mean exotropia to 6.0°± 6.5°(paired t-test, P < 0.001), corresponding to a 56% reduction in the ocular deviation. This reduction persisted during prolonged bilateral occlusion but reversed as soon as vision was restored. CONCLUSIONS.Bilateral occlusion reveals a fixation-free state of alignment that is different from orthotropia and usually less than the exotropia that occurs spontaneously during binocular viewing. This finding demonstrates that the deviation angle in patients with intermittent exotropia is actively mediated by visual feedback, which the fixating eye is capable of providing alone.

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Section: Resultsmentioning

confidence: 99%

“…Overlap in the 95% CIs indicates that the left exotropia was not significantly different from the right exotropia, as in most patients with intermittent exotropia. 22 …”

Section: Resultsmentioning

confidence: 99%

Bilateral Occlusion Reduces the Ocular Deviation in Intermittent Exotropia

Economides

Adams

Horton

2021

Invest. Ophthalmol. Vis. Sci.

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“…We also believe the difference in high spatial frequency cutoff is perhaps not so relevant in our testing because the visual stimulus was a bright LED against a dark background. Moreover, studies in humans by Economides and colleagues 32 , 33 have shown that a strong preference for fixation of the central cross does not influence the choice of eye used to acquire eccentric visual targets. Future testing of fixation preference using near-threshold stimuli could be used to investigate this issue further and test the framework more effectively.…”

Section: Discussionmentioning

confidence: 99%

Fixation Preference for Visual and Auditory Targets in Monkeys with Strabismus

Ramachandran

Das

2020

Invest. Ophthalmol. Vis. Sci.

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During binocular viewing, many strabismic subjects choose the eye of fixation depending on the retinotopic location of a visual target. Here, we compare eye choice behavior when orienting to visual and non-visual (auditory) targets. METHODS. Eye movements were measured in two head-fixed exotropic strabismic monkeys in a saccadic task involving either a visual or an auditory stimulus (no visual target information or feedback) during monocular or binocular viewing. The stimulus was one of 21 visual or auditory targets arranged 10°apart in a 7 × 3 array at a distance of 57 cm in an otherwise dark room. Fixation preference was calculated by recording the incidence of using a specific eye to acquire the target at any location. RESULTS. Spatial patterns of fixation preference were observed in both monkeys for both visual and auditory stimuli; targets to the far right were acquired by the right eye, and targets to the far left were acquired by the left eye. For visual targets, the border for a change in fixation preference occurred in between the visual axes of the fixating and deviated eyes (variable in the two animals). In contrast, the border for fixation change remained near the cranio-center during the auditory task. During monocular viewing, fixation switching was observed only at the extremities during visual tasks; during the auditory task, fixation preference was similar to that observed during binocular viewing. CONCLUSIONS. Fixation preference persists for invisible auditory targets. Our data suggest that visual suppression could modify underlying eye choice behavior that functions independently from vision.

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“…It is well recognized that surgical intervention decisions should be made more by the reference of a patient’s suppression depth rather than divergent degree alone, especially for children whose visual function is still developing. Normally, longer duration of deviation results in stronger visual suppression in patients with strabismus ( Adams et al, 2017 ; Cadet et al, 2018 ). However, the situation is much more complicated in IXT patients, as their visual suppression condition is unstable and varies with eye position ( Serrano-Pedraza et al, 2011 ; Wakayama et al, 2013 ).…”

Section: Introductionmentioning

confidence: 99%

“…However, the situation is much more complicated in IXT patients, as their visual suppression condition is unstable and varies with eye position ( Serrano-Pedraza et al, 2011 ; Wakayama et al, 2013 ). Patients with IXT can switch the fixating eye spontaneously according to the object position ( Adams et al, 2017 ; Ramachandran and Das, 2020 ). Thus, suppression can change between eyes depending on fixation.…”

Section: Introductionmentioning

confidence: 99%

A Dichoptic Optokinetic Nystagmus Paradigm for Interocular Suppression Quantification in Intermittent Exotropia

et al. 2021

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Purposes: To investigate the effectiveness of a dichoptic optokinetic nystagmus (dOKN) test to objectively quantify interocular suppression in intermittent exotropia (IXT) patients during the states of orthotropia and exodeviation.Methods: The OKN motion in subjects (15 controls and 59 IXT subjects) who viewed dichoptic oppositely moving gratings with different contrast ratios was monitored and recorded by an eye tracker. Interocular suppression in control subjects was induced using neutral density (ND) filters. The OKN direction ratios were fitted to examine the changes of interocular suppression in subjects under different viewing states. Two established interocular suppression tests (phase and motion) were conducted for a comparative study.Results: The dOKN test, which requires a minimal response from subjects, could accurately quantify the interocular suppression in both IXT and control subjects, which is in line with the established interocular suppression tests. Overall, although comparative, the strength of interocular suppression detected by the dOKN test (0.171 ± 0.088) was stronger than those of the phase (0.293 ± 0.081) and the motion tests (0.212 ± 0.068) in the control subjects with 1.5 ND filters. In IXT patients, when their eyes kept aligned, the dOKN test (0.58 ± 0.09) measured deeper visual suppression compared with the phase (0.73 ± 0.17) or the motion test (0.65 ± 0.14). Interestingly, strong interocular suppression (dOKN: 0.15 ± 0.12) was observed in IXT subjects during the periods of exodeviation, irrespective of their binocular visual function as measured by synoptophore.Conclusion: The dOKN test provides efficient and objective quantification of interocular suppression in IXT, and demonstrates how it fluctuates under different eye positions.

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Incomitance and Eye Dominance in Intermittent Exotropia

Cited by 18 publications

References 41 publications

Bilateral Occlusion Reduces the Ocular Deviation in Intermittent Exotropia

Bilateral Occlusion Reduces the Ocular Deviation in Intermittent Exotropia

Fixation Preference for Visual and Auditory Targets in Monkeys with Strabismus

A Dichoptic Optokinetic Nystagmus Paradigm for Interocular Suppression Quantification in Intermittent Exotropia

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