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Binocular Visual Acuity in Intermittent Exotropia: Role of Accommodative Convergence

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Binocular visual acuity in intermittent exotropia.

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 in the Study

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.

Results

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.

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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.

Furthermore, 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.

Frequently Asked Questions

What is visual acuity?

Visual acuity refers to the clarity or sharpness of a person’s vision, particularly in terms of their ability to discern fine details. It is a measure of how well a person can see objects at a specific distance. Visual acuity is often measured using a standardized eye chart, such as the Snellen chart, which consists of rows of letters or symbols of decreasing size. The chart is viewed from a certain distance, typically 20 feet (or 6 meters in some countries), and the smallest line of letters that a person can accurately read determines their visual acuity.

What is intermittent exotropia?

Intermittent exotropia is a type of strabismus. Strabismus is a visual disorder characterized by an imbalance in the alignment of the eyes, causing them to not properly work together to focus on an object. In the case of intermittent exotropia, one eye tends to deviate outward (away from the nose) at times, while the other eye maintains its normal alignment. This deviation can occur occasionally and is not constant, hence the term “intermittent.” The condition might manifest when the person is looking at distant objects, during periods of fatigue, or when they are not fully concentrating on their visual task.



Source:
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

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