Clinical and sensorial characteristics of microtropia.

PURPOSE To investigate the clinical characteristics and sensory mechanism of microtropia. METHODS Twenty patients with primary microtropia were studied. The patients were evaluated by the visuscope, Irvine prism test, Bagolini striated glasses test, Worth 4-dot test (W4D), TNO, and stereo-fly plate of the Titmus test. RESULTS The patients who had positive cover test and eccentric fixation showed wandering eccentric fixation. The Irvine prism test was positive in all the patients by using prisms of different strengths and positions. All the patients had abnormal fusion at near. At distance, 15 patients had abnormal fusion by the Bagolini glasses and 8 patients had abnormal fusion by the Worth test. Ten patients had gross stereopsis and the remaining 10 had no measurable stereopsis. CONCLUSIONS The type of microtropia with eccentric fixation without identity is mainly due to the wandering eccentric fixation. All patients with microtropia have abnormal fusion without fixation point scotoma because positive prism test response does not change to normal by using prisms of different strengths and positions. Differences in fusion results are mainly due to the weakness of abnormal fusion rather than fixation point scotoma. With occlusion treatment, amblyopia can be improved, whereas binocular defects of microtropia cannot be improved.