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Krista R Kelly, Joost Felius, Santoshi Ramachandran, Blesson John, Reed M Jost, Eileen E Birch; Disparity vergence in infantile esotropia reveals a congenital deficit for disparity sensitivity. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3192. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Impaired disparity sensitivity (e.g., decreased stereoacuity) in children with infantile esotropia (ET) is thought to be a result of prolonged abnormal visual experience during an early critical period of visuomotor maturation. Even with early treatment, a stereodeficit persists in children with infantile ET. Thus, it is unclear whether the stereodeficit is entirely a consequence of abnormal visual experience or whether, at least in part, the deficit is congenital. Here, we sought to answer this question by examining disparity vergence in non-amblyopic, orthotropic children with infantile ET who experienced a short or long duration of constant misalignment.
We tested three age-matched groups of children (7.8±2.8 y); 15 controls with a history of normal visual development, 10 infantile ET with a short duration (≤3 months) of constant misalignment, and 8 infantile ET with a long duration (>3 months) of constant misalignment. Disparity vergence was recorded using a 500 Hz remote-video binocular eye tracker (EyeLink 1000; SR Research) following binocular calibration. The child initially fixated on an LED located on midline at 80 cm, which was extinguished and replaced by an LED on midline at 30 cm, requiring a vergence response. A total of 10 vergence responses were recorded and at least 3 artifact-free responses were required for analyses. Mean response gain (vergence angle/vergence demand) was calculated.
Compared with controls, short and long duration of infantile ET resulted in a 22% and 54% decrease in disparity vergence gain, respectively (p ≤ 0.009). Even those with 0 months duration of constant misalignment (i.e., infantile accommodative intermittent ET) exhibited a 20% decrease in vergence (p = 0.012) compared with controls. Further, long duration of infantile ET resulted in a decrease of 41% compared with short duration (p = 0.037). While 14/15 controls showed smooth disparity vergence, 5/10 short duration ET and 7/8 long duration ET children exhibited pure saccades, a combination of saccades and vergence, or vergence combined with saccadic oscillations or nystagmus.
Impaired disparity vergence following zero and short duration of constant misalignment indicates that a congenital deficit in disparity sensitivity is present in children with infantile ET, which can be exacerbated by prolonged abnormal binocular visual experience.
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