1. An image processing apparatus comprising: a detection unit configured to detect layers on the retina based on tomographic images of the retina; a calculation unit configured to calculate for each of a plurality of positions on a boundary surface between the retina and the corpus vitreum an index for indicating the degree of curvature of the boundary surface; an acquisition unit configured to acquire a region having a largest curvature of the boundary surface by using the index; and a determination unit configured to determine an optic disc of the retina based on a region where a specific layer is not detected by the detection unit and the region acquired by the acquisition unit, wherein the index for evaluating the degree of curvature is at least one of a gradient value, and a depth directional variation on the boundary surface in a predetermined range at each of the plurality of positions on the boundary surface, the predetermined range including the respective position.