Is Inverse Prism Therapy Comparable to Conventional Prism Therapy for Improving Newcastle Scores in Patients with Basic Intermittent Exotropia?

ABSTRACT Purpose: To determine the effect of prism orientation on the Newcastle Control Score (NCS) in patients with basic intermittent exotropia (IXT). Methods: Patients with IXT with a distant angle of deviation (DAD) ≤50∆ and NCS≥5 were recruited and randomly divided into two groups. The inverse prism (IP) group received a base-out Fresnel prism addition to achieving full refractive correction, and the conventional prism (CP) group received base-in Fresnel prism addition. The prism addition was equivalent to one-third of the mean DAD. Patients were evaluated 3 months after initial treatment, 3 months after partial weaning and 6 months after complete weaning. NCS and DAD values were compared. Tolerance was defined as the ability to wear the prescription 80% of waking hours. Results: Fifty patients were enrolled in each group. The IP group had 6 intolerant patients, and the CP group had 3 intolerant patients. NCS improved in both groups (from 6.2 ± 0.7 to 3.4 ± 2.5 in the IP group and from 6.4 ± 0.7 to 3.7 ± −2.2 in the CP group). However, the final NCS difference was nonsignificant (Mann-Whitney, p = .6). The DAD changes were not significantly different between the 2 groups (t-test = 0.04). The average DAD decreased from 31.9 ± 6.9∆ to 10.11 ± 11∆ in the IP group and from 30.7 ± 8.5∆ to 15.5 ± 13.5∆ in the CP group. Four patients in the CP group exhibited an increase in DAD. Conclusion: The two types of prism therapy showed comparable improvements in NCS.