Clinical exhibition of increased accommodative loads for binocular fusion in patients with basic intermittent exotropia

A total of 17 patients and 15 normal controls were included in this study. The mean
age was 10.0?±?4.09 years (range, 5 to 20) in the IXT patients and 9.1?±?2.58 years
(range, 6 to 14) in the controls. Eight (53.1 %) IXT patients and 8 (46.9 %) controls
were female. The mean angle of deviation in the IXT patients was 20.2?±?7.19 PD (range,
12 to 35). Table 1 displays the basic patient characteristics.

Table 1. Baseline patient characteristics

In the fixating eye of IXT patients, the amount of accommodative load was significantly
greater under binocular viewing than it was under monocular viewing during near target
fixation (50, 33 and 20 cm) (p?=?0.028, 0.001, 0.006 respectively). However, the accommodative loads during distant
target viewing did not increase significantly (p?=?0.193). Similarly, in the deviating eye of IXT patients, the amount of accommodative
load under binocular viewing was also significantly greater than was that under monocular
viewing during near target fixation (50, 33 and 20 cm) (p?=?0.022, 0.003, 0.003 respectively). There were no significant changes in the accommodative
loads during distant target viewing (p?=?0.155). Tables 2 and 3 compare the refractive errors between monocular and binocular viewing conditions
in IXT patients. The changes of accommodative loads for both fixating and deviating
eyes increased as the target got closer (p?=?0.047, 0.026, Kruskal-Wallis test).

Table 2. Accommodative load in the fixating eye of IXT patients

Table 3. Accommodative load in the deviating eye of IXT patients

However, there was no significant difference in the changes of accommodative loads
with distance in normal controls (6 m, 50 cm, 33 cm and 20 cm) (p??0.05, all). In addition, there were no significant differences between the right
and left eyes in control patients. The changes in accommodative loads were also not
significantly different according to the target distance (Tables 4 and 5).

Table 4. Accommodative load in the right eye of normal controls

Table 5. Accommodative load in the left eye of normal controls

While viewing distant targets, there were no significant differences in accommodative
load change between the fixating eye of IXT patients and the right eye of control
patients (6 m) (p?=?0.097). However, while viewing near targets (50, 33 and 20 cm), there were significantly
greater changes in accommodative loads in the fixating eyes of IXT patients than there
were of right eyes from controls (p?=?0.027, 0.002, 0.002, respectively). These results are similar to the changes in
accommodative loads of the deviating eyes in IXT patients compared to those of left
eyes from controls. During distant target (6 m) viewing, there were no significant
differences in accommodative load change between the deviating eyes of IXT patients
and the left eyes from controls (p?=?0.278). However, during near target viewing (33 and 20 cm), there were significantly
greater changes of accommodative loads in the deviating eye of IXT patients than there
were of left eyes from controls (p?=?0.002, 0.003). Table 6 compares the changes of accommodative loads between IXT patients and controls.

Table 6. Comparing increases in accommodative load from monocular to binocular viewing between
IXT patients and controls

Among IXT patients with a confirmed fixation preference, there were no significant
differences in accommodative load change between fixating and deviating eyes at each
target (p??0.05, all, Table 7).

Table 7. Comparing the increase in accommodative load from monocular to binocular viewing between
the fixating and deviating eyes of IXT patients with fixation preferences