Abstract
BackgroundTo investigate the accommodative loads change needed to maintain binocular fusion in patients with intermittent exotropia (IXT).MethodsSeventeen consecutive patients with basic IXT and 15 normal controls were recruited. The WAM-5500 autorefractor (GrandSeiko, Fukuyama, Japan) was used to measure refractive error (D) under binocular and monocular viewing conditions at 6 m, 50 cm, 33 cm and 20 cm. The difference between binocular and monocular refractive error (D) at each distance defined the change in the accommodative load. The changes in accommodative load were compared between IXT patients and normal controls. We also investigated the change in accommodative loads according to the fixing preference in patients with IXT.ResultsIn IXT patients, the mean angles of deviation were 20.2 ± 7.19 and 21.0 ± 8.02 prism diopters at 6 m and 33 cm, respectively. Under binocular viewing, the changes in accommodative loads of each eye in IXT patients were significantly higher at 50, 33 and 20 cm than those of normal controls (p < 0.05, all). The changes in accommodative loads of fixating and deviating eyes at 6 m were not significantly different between IXT patients and normal controls (p = 0.193, 0.155, respectively). The changes in accommodative loads of the fixating eye at each distance were not significantly different from those of the deviating eye in IXT patients (p > 0.05).ConclusionThe changes of accommodative loads at near fixation increased more in IXT patients than they did in normal controls while maintaining binocular fusion.
Highlights
To investigate the accommodative loads change needed to maintain binocular fusion in patients with intermittent exotropia (IXT)
In the fixating eye of IXT patients, the amount of accommodative load was significantly greater under binocular viewing than it was under monocular viewing
Our study shows that there is a 0.97 D increase in accommodation from monocular to binocular viewing
Summary
To investigate the accommodative loads change needed to maintain binocular fusion in patients with intermittent exotropia (IXT). Intermittent exotropia (IXT) is the most common form of childhood exotropia [1, 2] and is more prevalent in Asian children [3]. Esotropia is associated with hyperopia and anisometropia, [4,5,6] the refractive error in patients with intermittent exotropia has not been extensively studied. A previous American populationbased study found that 135 children with IXT showed a significant trend toward myopia over time [7]. Myopia is prevalent in Asian populations; interestingly, In the presence of IXT, binocular fusion requires more effort from the vergence system to produce additional convergence. Maintaining binocular motor fusion requires convergence to compensate for IXT.
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