: To evaluate the adding effect of inward decentration of concave spectacle lenses (adding a prismatic effect) on angle control in cases with distance intermittent exotropia (IXT) receiving over-minus therapy. : Patients with myopia with IXT angles ≤25 and a Newcastle score (NCS) ≥5 were included. Patients were randomised into two groups. Group 1 received over-minus therapy. Group 2 received over-minus therapy with inward decentration of spectacle glasses to add a base out prism effect equal to one-third of the distance angle of deviation. Success was measured as the percentage of orthotropic cases or those with orthophoria or IXT with improved NCS ≤ 3 and tolerant to treatment. Patients were evaluated 3 months after initial treatment, 3 months after partial weaning and 18 months after complete weaning. : Sixty-four patients were included, with 32 in each group. The success rates of group 1 were 65.6%, 37.5%, and 31.3%, in group 2, the rates were 75%, 65.6%, and 65.6% for orthotropic cases or those with orthophoria or IXT with improved NCS ≤ 3, respectively. Moreover, NCS significantly improved in group 2 till last visit. : Adding decentration to over-minus therapy can result in better control of small angle IXT and could be considered as a non-invasive and reversible therapy.