Primary microtropia is a clinical entity defined by anomalous retinal correspondence of less than 5°. Heredity plays a role. Fixation may be central or eccentric. Anisometropia or heterophoria are additional, but not essential, findings. Microtropia helps achieve a better understanding of amblyopia and of pathogenesis of strabismus. However insignificant microtropia is from the cosmetic point of view, it may be important to factors in strabismus.
Lang J. Microtropia. Arch Ophthalmol. 1969;81(6):758-762. doi:10.1001/archopht.1969.00990010760002