Measures of binocular motility were compared for three groups of parents in order to examine trends in parent-offspring resemblance. These groups included parents of offspring with esotropia (S-ET), parents of offspring with exotropia (S-XT), and parents of children without deviation (R). Both parent groups of affected individuals displayed lower measures of relative fusional amplitude than parents of normal offspring. This difference was significant for the female comparison. There seemed to be a consistent sex difference within each group for certain measures. Comparison of the incidence of underacting lateral recti revealed differences between the R group (15%) and the S-ET and S-XT groups (both about 30%). The incidence of medial rectus underaction was found to be different for the S-XT group (about 18%) and the S-ET (about 6%) and the R (about 3%) groups.
Niederecker O, Mash AJ, Spivey BE. Horizontal Fusional Amplitudes and VersionsComparison in Parents of Strabismic and Nonstrabismic Children. Arch Ophthalmol. 1972;87(3):283-285. doi:10.1001/archopht.1972.01000020285009