A complete ophthalmologic and orthoptic examination was carried out in 167 families (comprised of 928 individuals). Selected variables from the examination have been chosen for analysis. The members of each family were grouped according to the deviation exhibited by the propositus, eso or exo (whether phoria, intermittant, or tropia), or none. However, all propositi were excluded from the analysis. Even with this method of lumping phorias and tropias (which would seem to minimize differences between groups) statistically significant differences were found. With a more strict definition of strabismus and more families, we will be able to establish a statement of the heritability of the various measured variables in strabismus.
Smith D, Grützner P, Colenbrander A, Hegmann JP, Spivey B. Selected Ophthalmologic and Orthoptic Measurements in Families. Arch Ophthalmol. 1972;87(3):278-282. doi:10.1001/archopht.1972.01000020280008