Abstract
From a study of a large number of brothers and sisters suffering from concomitant squint, the following data were obtained: (1) 42-9% of the patients showed congenital strabismus. (2) In 96-5% of the sibs strabismus was of the same type. (3) The presence of a significant refractive error occurred in 82-8% of the patients. (4) In all twins strabismus appeared at the same age in both twins, and the squint and the refractive error were of the same type. (5) The distance of the patients' homes from Athens had no effect on either (a) the time intervening between the onset of squint and the first visit to the eye specialist, or (b) the effectiveness of treatment.