Evaluation of binocular summation ratio before and after vision training in patients with intermittent exotropia: A pilot prospective cohort study

Purpose

To investigate the binocular summation ratio (BSR) in intermittent exotropia (IXT) before and after vision training under varying light conditions, and to evaluate its association with the control of deviation.

Methods

Twenty IXT patients were included in the study. Patients were divided into three groups based on their control of deviation: poor, fair, and good control. Contrast sensitivity was assessed using the CSV1000-HGT chart at four spatial frequencies, evaluated both monocularly and binocularly from a distance of 2.5 meters. This evaluation occurred under both photopic and mesopic lighting conditions, with and without glare. Additionally, the BSR for each patient was calculated before and after the vision training process.

Results

The mesopic BSR under glare-free conditions demonstrated a significant increase following vision training. In the presence of glare, the mesopic BSR significantly increased across all spatial frequencies: 3, 6, 12, and 18 cycles/degree. Additionally, after vision training, the photopic BSR in glare-free conditions also showed an increase at all frequencies. However, under glare conditions, the photopic BSR only increased at the frequencies of 3, 12, and 18 cycles/degree, but this increase was not statistically significant. A significant increase in the BSR was observed only at the frequency of 6 cycles/degree. Furthermore, following vision training, the degree of control over deviation improved significantly.

Conclusion

The BSR and deviation control scores in patients diagnosed with IXT demonstrated significant improvement following vision training, underscoring the efficacy of this treatment method in the management of IXT.