Retinal curvature and geometry of image formation

We investigate the geometry of the whole image that forms on the hemispherical back of human eye. In view of the Gauss Egregium Theorem the hemispherical form of the back prevents an isometric representation of the external world, unless it be described as union of hemispheres centered on the eye. We make some calculations to verify the position of the second nodal point in paraxial optics and then, reasoning on the non-paraxial part, we speculate that the cooperation of the optical system with the brain is capable of establishing such an isometry. It follows that we have a "spherical vision" of the world, and we elaborate on this concept touching topics like perspective, sensor pattern, art and technology.