I hypothesize that the functional role of binocular correspondence, whether normal or anomalous, is that of detecting retinal disparity stimuli. Normal correspondence involves disparity stimulus detection that is quantitatively normal and stable, whereas anomalous correspondence involves disparity detection that is quantitatively abnormal and variable. Normal disparity stimuli typically produce motor fusion between normally corresponding biretinal areas. The result is orthotropia, which permits normal single binocular vision and acute stereopsis. In contrast, abnormal disparity stimuli typically produce motor fusion between anomalously corresponding areas. The result is strabismus, usually coupled with anomalous single binocular vision (harmonious anomalous correspondence). Accordingly, corrective prism or muscle surgery only produces vergence movements that restore anomalous motor fusion, rather than eliminating the heterotropia. The inference is that anomalous correspondence involves a neurological disorder in the disparity detection mechanism, either on the convergent side (estropia with anomalous correspondence) or divergent side (exotropia with anomalous correspondence).