To explore the factors related to eye position control in basic intermittent exotropia (IXT).

A total of 434 patients (868 eyes) with basic type IXT from the Eye Center of Beijing Tongren Hospital affiliated to Capital Medical University from March 2021 to September 2023 were collected. Among them, there were 215 males (430 eyes) and 219 females (438 eyes) with a median age of 9.83 (8.23, 11.63) years (ranging from 4 to 20 years old). The eye position control was performed by Newcastle control scale (NCS). According to the NCS results, they were divided into good control group and poor control group. The refractive status, strabismus, stereoscopic vision, adjustment function, and convergence function of all patients were performed. Age, refractive status, strabismus, near stereoscopic vision, adjustment function, and collection function did not follow a normal distribution after normality testing, and were expressed as M (Q1, Q3) and compared by rank sum test for inter group. Far stereoscopic vision was expressed by percentages, and compared by χ² for inter group. The factors of IXT control force was to analyze by logistic regression.

The equivalent spherical refractive index (SE) of the main eye, non main eye SE, near and far strabismus, and near stereopsis of patients with good control were -1.25 (-2.75, 0.50) D, -1.38 (-2.78, 0.75) D, -30 (-40, -25) PD, -25 (-35, -20) PD, and 2.30 (2.15, 2.90) Log arc seconds, respectively. The patients in the group with poor control were -0.00 (-1.75, 0.88) D, -0.25 (-1.88, 1.00) D, -50 (-60, -40) PD, -50 (-60, -35) PD, and 2.60 (2.15, 3.20) Log arc seconds, respectively. The group with good control had higher myopia diopter in both the primary and non primary eyes, smaller near and far strabismus, and better near stereoscopic vision, and the differences were statistically significant (Z=-3.314, -3.047, -11.803, -12.328, -2.785; P<0.05). The far standing stereoscopic preservation rates of patients with good control and poor control were 65.58% and 36.79%, respectively. The patients with good control had a higher preservation rate of distant stereoscopic vision, and the difference was statistically significant (χ ²=33.079, P<0.05). The adjustment flexibility of the dominant eye, non dominant eye, and binocular vision in patients with good control were 9.00 (6.63, 11.00) cpm, 8.50 (6.50, 11.00) cpm, and 7.75 (6.00, 10.00) cpm, respectively. The patients in the poor control group had 7.50 (6.00, 10.00) cpm, 7.50 (6.00, 9.25) cpm, and 7.00 (5.00, 9.00) cpm, respectively. The patients with good control had better primary vision, non primary vision, and binocular adjustment flexibility than those in the group with poor control, and the differences were statistically significant (Z=-4.065, -3.666, -2.690; P<0.05). The patients with good control had a total range of far and near images, a reserve rate for far and near images, an accommodative convergence/accommodation (AC/A) ratio, a reserve rate for far and near images, and a reserve rate for far and near images, which were 50.50 (35.75, 59.00), 55.00 (47.50, 65.00), 0.76 (0.51, 1.16), 0.77 (0.51, 1.11), 2.00 (1.00, 4.00), 22.00 (16.00, 27.00), and 24.00 (18.00, 30.00), respectively; The patients with poor control were 65.00 (55.25, 77.00), 70.00 (58.50, 84.00), 0.50 (0.31, 0.72), 0.51 (0.34, 0.65), 2.33 (1.00, 4.00), 22.00 (16.00, 28.00), and 24.00 (18.00, 30.00), respectively. The patients with good control had smaller total collection amplitude at far and near distances, and larger reserve rates for far and near distance fusion images, with statistically significant differences (Z=-7.439, -6.435, -5.709, -6.254; P<0.05); However, there was no statistically significant difference in AC/A, far set reserve, and near set reserve (Z=-0.845, -0.469, -0.798; P>0.05). After multivariate logistic regression analysis, the factors that affect the control of eye position in IXT patients, non dominant eye SE, distant stereo vision, near range collection amplitude, and near fusion image reserve rate were statistically significant (OR=1.220, 95%CI: 1.044 to 1.427, P<0.05), (OR=0.399, 95%CI: 0.203 to 0.785, P<0.05), (OR=1.050, 95%CI: 1.027 to 1.074, P<0.05), and (OR=0.149, 95%CI: 0.054 to 0.412, P<0.05).

The control in basic IXT is primarily influenced by convergence rather than accommodation. The control in basic IXT may be primarily driven by the near convergence.