Abstract: Microtropia and the monofixation syndrome (MFS) can be used to describe the small angled squint with abnormal binocular function. Because of their confusing clinical features, attention should be paid to differential diagnosis. Both of them can be classified into three types: primary, secondary and decompensated. In addition, according to the result of cover test, microtropia can be classified into microtropia with identity and microtropia without identity. According to the direction of deviation, microtropia can be classified into micro-esotropia, micro-exotropia and micro-hypertropia. Microtropia and the MFS might be due to a residual of large strabismus, decompensated heterophoria, anisometropia or heredity, but the exact cause remains unknown. The clinical characteristics include small angled heterotropia, anomalous retinal correspondence, eccentric fixation, central scotoma, amblyopia and some degree of stereoacuity and peripheral fusion. For the diagnosis of microtropia, small angled heterotropia is essential，while central scotoma is not. For the diagnosis of the MFS, central scotoma is essential，while small angled heterotropia is not. Therapies for the two conditions are similar, including correction of the anisometropia, occlusion, synoptophore, prism and surgery.  (Int Rev Ophthalmol, 2015, 39：165-169)