1. An image processing apparatus comprising: a storage unit configured to store a plurality of tomographic images in relation to fundus of an examined eye of a patient; a detection unit configured to detect a boundary of retinal pigment epithelium and an inner limiting membrane from each of the plurality of tomographic images and to detect a part where the boundary of the retinal pigment epithelium is discontinuous; a determination unit configured to determine a surface of a sclera model for each of the plurality of tomographic images by use of the boundary of the retinal pigment epithelium and the inner limiting membrane; a generation unit configured to generate a sclera model including an optic papilla periphery by use of the surface of the sclera model and the part where the boundary of the retinal pigment epithelium is discontinuous; a combining unit configured to combine each of the plurality of tomographic images and the sclera model to generate a combined image; and a display unit configured to display the combined image generated by the combining unit.