AIM:To assess the quantitative association between anisometropia magnitude and the losses of resolution and contrast sensitivity; and to exemplify how the function of fusion and stereopsis vary with anisometropia magnitude (AM) in previously untreated anisometropic amblyopes.METHODS:A total of 57 patients with previously untreated anisometropic amblyopia without strabismus (range:8-35 years), were measured refractive error, best corrected visual acuity (BCVA), fusion and stereopsis, and 48 patients have completed contrast sensitivity function test. AM was determined by dioptric vector addition model, and the amblyopia depth was determined by the difference of BCVA in logMAR units between the amblyopic and fellow eyes.RESULTS: AM was significantly correlated with both amblyopia depth (Pearson R=0.728, P<0.001) and the inter-ocular difference of the area under the log contrast sensitivity function (AULCSF) (R=0.505, P<0.001). Depth of amblyopia and the inter-ocular difference of AULCSF was also significantly correlated (R=0.761, P<0.001). The more severity of amblyopia, the poorer levels of contrast sensitivity. Most pure anisometropes with AM was less than 3.0D retain fusion and some stereopsis, but when AM were more than 3.0D, especially for the anisometropes whose AM was more than 6.0D, fusion and stereopsis function were seriously impaired.CONCLUSION: In the patients with previously untreated anisometropia amblyopia, higher degree of anisometropia is significantly associated with deeper amblyopia, worse contrast sensitivity, fusion and stereopsis functions.