Impact of prism adaptation test on distance-near-deviation before strabismus surgery in patients with intermittent exotropia.

Purpose: To evaluate the effect of preoperative prism adaptation test (PAT) on the angle of squint in intermittent exotropia (XTint).

Methods

In this single-center retrospective study, we reviewed the medical records of patients with the diagnosis of XTint, aged at least 12 years, who were treated by strabismus surgery for the first time. The maximum angle of squint (AOS) for far (F) and near (N) fixation and PAT results before surgery as well as AOS (F) and AOS (N) after surgery and results of binocular function tests were considered. PAT included wearing a prism based on the largest angle for about 60 min, without changing the prism power.

Results

One hundred patients (between 12 and 78 years, mean age 32 ± 17 years) were included in the study. Before surgery, AOS was -33.6 ± 13.3 pdpt (F) and -34.4 ± 15.5 pdpt (N). After PAT, the mean AOS was not significantly different with AOS(F) = -32.7 ± 12.4 and AOS(N) = -34.6 ± 12.9 pdpt (p ≥ .057). However, in 82% of patients, AOS (F) and/or AOS (N) in- or decreased by at least 3 pdpt after PAT. The absolute distance-near difference (DND) was 6.6 ± 7.1 pdpt before PAT. After PAT, it was significantly lower with 3.5 ± 3.3 pdpt (p < .001).

Conclusion

In 82% of patients with XTint, there was a change in AOS of more than the dose relevant angle change of ≥3 pdpt. The absolute distance-near difference decreased significantly after PAT. Therefore, we recommend using a PAT for preoperative examination of patients with XTint.