Assessment of distance-near control disparity in basic and divergence excess paediatric intermittent exotropia

ABSTRACT

Clinical Relevance

In intermittent exotropia (IXT), deviation is better controlled at near fixation. Understanding of the mechanism responsible for this common observation may improve clinical management of IXT.

Background

The physiological basis for the distance-near difference in control of deviation in IXT is vastly undetermined. A new parameter, ‘control score disparity (CSD)’, defined as the difference between distance and near control scores, is introduced. Association of CSD with positive fusional amplitude (PFA), accommodative convergence to accommodation (AC/A) ratio and distance angle of deviation was investigated to further understand the mechanisms.

Method

Patients aged between four and fifteen years with basic and divergence excess IXT were included. Subjects with previous strabismus surgery, amblyopia and inability to perform clinical tests were excluded. A standardized office-based scoring system was used to assess IXT controls. Subjects were sub-divided into group 1 (CSD <2) and group 2 (CSD ≥2). Pearson’s univariate and regression analysis were used to determine relationships between CSD and other independent variables.

Results

Mean age of the total 141 subjects (57.6% female) was 6.8 ± 2.5 years. Basic IXT was more common (60%) and 60% had CSD ≥2. The mean±SD distance angle of deviation, AC/A ratio, PFA and CSD were 22.1 ± 6.6 prism dioptres, 5.0 ± 1.0, 28.6 ± 6.3 prism dioptre and 2.0 ± 0.5, respectively. CSD was significantly correlated to PFA (r = 0.64, p < 0.001) and AC/A ratio (r = 0.27, p < 0.001) in overall samples and Group 2 subjects (r = 0.41, p = 0.001).

Conclusions

PFA is a major factor associated with the distance/near difference of IXT control. Individuals with a higher PFA demonstrated greater CSD. While AC/A ratio was associated in better control at near in divergence excess IXT, magnitude of angle appears irrelevant.

KEYWORDS:

• Control score disparity
• intermittent exotropia
• IXT control score
• positive fusional amplitude

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The study was supported by Queensland Children’s Hospital through ‘Study Education and Research Trust Account (SERTA)’ funding scheme.