at the first medical examination , the sister was 7 years 8 months old , and the brother was 5 years 3 months old . neither sibling had any specific birth history . slit lamp microscopic examination revealed no abnormalities in the anterior segments of either eye , in either patient . the best corrected visual acuities ( bcva ) were 0.1 ( right eye ) and 0.8 ( left eye ) in the sister , and 0.7 ( right eye ) and 0.1 ( left eye ) in the brother . the cycloplegic refractive powers in the sister were : -15.50 diopter ( dpt ) , cylinder ( cyl ) + 4.50 dpt ax 85 in the right eye and -1.00 dpt cyl . the differences in spherical equivalents between the two eyes were -12.50 diopters in the sister and -6.875 diopters in the brother . full - time right occlusion therapy was performed in both patients for three months , then four to six hours a day for two years . the sister was prescribed atropine for the left eye after six hours right - sided occlusion therapy a day for a year . three years later , the bcva in the brother 's left eye had improved from 0.1 to 0.7 . the bcva in the sister 's left eye improved from 0.1 to 0.7 during the first year ; however , she showed no further improvement after that time . the refraction and the radius of the anterior corneal curvature were measured using an autorefractokeratometer ( speedy - k ; nikon , tokyo , japan ) and a topographer ( orb - scan ; bausch & lomb , rochester , ny , usa ) . a - mode ultrasonography ( cinescan ; quantel medical , clermont - ferrand , france ) was performed . the results of a - mode ultrasonography and orb - scan are presented in table 2 . this condition is often associated with amblyopia , both in the presence of and in the absence of strabismus [ 6 , 7 ] . the prevalence of anisometropia reported in school - based and population - based studies of school - aged children is typically 5% , but this figure varies depending on the manner in which anisometropia is defined . myopic anisometropia is usually accompanied by strabismus , especially exotropia in 30 - 60% of patients . this suggests that the development of binocular vision might be affected by mild infantile exotropia . when high myopia of one eye is more than -5 to -6 diopters , or the difference in spherical equivalents of both eyes is more than 5 diopters , then anisometropia may be responsible for amblyopia . , the present case is without any obvious complication and shows mirror image similarly . in the study of 78 monozygotic twins and 40 dizygotic twins , sorsby et al . reported that the concordances of corneal power , axial length , and vertical ocular refraction were higher in monozygotic twins than in dizygotic twins . interestingly , patients in the present study had similar axial lengths in their myopic eyes . in conclusion , we believe that severe myopic anisometropia may be genetically determined , and further investigation is recommended .