Researchers had the opportunity to study a pair of genetically identical twins diagnosed with strabismus, which eliminated any genetic differences that might affect the disease process or treatment outcomes. Twin one was diagnosed at six months of age, while twin two was diagnosed at age five. Both underwent corrective surgery soon after diagnosis. Monocular and binocular visual function testing revealed earlier onset of the condition led to poorer visual outcomes, despite corrective measures.1

Twin one had worse contrast sensitivity than her sister, and she had complete suppression and unmeasurable stereoscopic function. Twin two, however, demonstrated fusion and had only mild suppression and near-normal stereoscopic function.1

“To the best of our knowledge, this represents the first study of a genetically identical sibling pair with strabismus,” the researchers said. “By eliminating the genetic differences between these patients, we are able to make powerful observations about the effect of environment on visual function in strabismus.”1

“This article is noteworthy because its confirmation of the identically genetic composition of these twins places a spotlight on the influence of environmental factors on binocular development,” said Leonard J. Press, OD, in a PracticeUpdate release. “The authors suggest that interventions designed to maintain binocular interaction at a young age may be crucial in guiding successful binocular outcomes in adulthood. Longitudinal studies of identical twins with differing levels of binocular vision in infancy will shed further light on this intriguing case report.”2

1. Cadet N, Huang PC, Superstein R, et al. The effects of the age of onset of strabismus on monocular and binocular visual function in genetically identical twins. Can J Ophthalmol. April 7, 2018. [Epub ahead of print].
2. Age of strabismus onset affects monocular and binocular visual function. PracticeUpdate. May 2, 2018.