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Binocular visual acuity in intermittent exotropia: Role of accommodative convergence

Boy with glasses

In this blog, we summarized some key points from Ahn et al. article. Research from Ahn et al. (2012) investigated binocular interaction of visual acuity (VA) in patients with intermittent exotropia and its relationship with accommodative responses during binocular vision. Patients included were aged between 8 and 15 years with intermittent exotropia at distance or near. A comprehensive ophthalmologic examination was completed on all patients by a pediatric ophthalmologist. Moreover, a professional examiner used the Snellen chart to record distance visual acuities. To avoid disrupting fusion, binocular visual acuity was recorded first, and monocular VAs of both eyes were examined after occluding one eye in a random order. They were also measured for accommodative response, and they filled quality-of-life questionnaire to evaluate the impact strabismus has on their quality of life.

Binocular interaction of visual acuity: Binocular equivalence was seen in the majority of individuals (60.3%). Roughly 30% of individuals had binocular summation (an increase in binocular performance over monocular performance), while 9.5% had binocular inhibition. However, the mean angle of exodeviation at a distance differed significantly between the three groups, with binocular inhibition patients having the highest deviation. Patients with binocular inhibition (50%) had a recent increase in the frequency or severity of exodeviation, which was marginally significant across the three groups. In patients with intermittent exotropia, there was a strong link between binocular VA and improved monocular VA.

Relationship between binocular visual acuity minus monocular visual acuity difference and accommodation: The positive r value implies that when accommodation improves, the difference between binocular VA and monocular VA (logMAR) grows, implying that binocular VA decreases.

Relationship between accommodation and the size of exodeviation: In patients with intermittent exotropia, the accommodative response increases as the angle of exodeviation at distance increases.

Relationship between binocular interaction and distance stereoacuity: Binocular inhibition resulted in poor distant stereoacuity in all individuals.

Relationship between quality-of-life questionnaire and binocular visual acuity minus monocular visual acuity difference or accommodation: Researchers did not find any significant relationship.

Relationship between age and binocular interaction: Between the two age groups, there were no significant differences in binocular and improved monocular VA or accommodative response during binocular vision.

Conclusion

Results of this study showed that in patients with intermittent exotropia, binocular interaction of visual acuity is associated with accommodative response during binocular vision. The angle of exodeviation at distance was shown to be substantially linked with accommodative amplitudes, implying that accommodative convergence used to maintain ocular alignment may impact binocular interaction of VA in patients with intermittent exotropia. This study demonstrated the usefulness of binocular VA in patients with intermittent exotropia. As a result, researchers believe that, in addition to stereoacuity, the pattern of binocular interaction can be utilized as a measure of fusional control.

Ahn, S. J., Yang, H. K., & Hwang, J. M. (2012). Binocular Visual Acuity in Intermittent Exotropia: Role of Accommodative Convergence. American Journal of Ophthalmology, 154(6), 981–986.e3. https://doi.org/10.1016/j.ajo.2012.05.026