Natural clinical course and risk prediction for prognoses of untreated intermittent exotropia with small deviation in Chinese children aged 3–9 years: a single-centre prospective observational study

To investigate the natural course and clinical characteristics of intermittent exotropia ( IXT) with small deviation in Chinese children in a 1-year observation, and to identify the risk predictors for IXT progression. Exodeviation, Holmes control score, stereo vision, and convergent fusion were assessed and compared between patients with and without IXT progression. COX regression analysis was conducted to identify risk factors for IXT progression. IXT progression was defined by any one of the following criteria:1) an increase in the angle of exodeviation by ≥ 10 prism diopers (PD) either at distance or at near; 2) an increase in the Holmes control score by > 2 points; 3) a decrease in stereopsis by > 2 grades. Eighty nine patients aged 3 to 9 years with IXT of 10 to 25 PD at the initial visit were enrolled. Over 1-year observation period, 41.57% patients manifested IXT progression, 43.82% remained stable, and 14.61% showed improvement. The constituent ratio of IXT prognoses differed significantly between children aged 3–5 years (n = 25) and those aged 6–9 years (n = 74) ( Z = 7.590, P = 0.020). The progression rate was significantly higher, reaching 56%, in the 3–5 years group compared to 35.9% in the 6–9 years group. At the final visit for children aged 6–9 years, there were significant differences in the amplitude of convergent fusion at both distance and near (P = 0.0225, 0.0304, respectively), as well as fusion reserve ratio at both distance and near (P = 0.0078, 0.0067) between progression and non-progression patients. Multivariate COX regression analysis revealed that the amplitude of convergent fusion at near and the Holmes control score were significant predictors of IXT progression (P = 0.023, HR = 0.9662, 95%CI 0.9381–0.9953 and P = 0.023, HR = 1.3691, 95%CI 1.0457–1.7925). In Chinese children aged 3 to 9 years, the rate of IXT progression was about 40% over 1-year observation period, based on motor and sensory aspects. The key risk factors for IXT progression were the control score and the amplitude of convergent fusion at near.