Influences of chorion type on saccadic eye movements in twins

The influence of genetic and prenatal environmental factors on characteristics of saccadic performance were evaluated in young monozygotic (MZ) twins (8-19 years old) of known chorion type. Saccadic eye movements were recorded using an infrared system. Saccadic latency, accuracy, and parameters of amplitude-peak velocity exponential equation (main sequence) were quantified. Intraclass correlations of saccadic parameters differed significantly from zero for monochorionic and dichorionic MZ twins. The within-pair mean squares were significantly less, and intraclass correlations were significantly higher in monochorionic than in dichorionic twins for latency and were similar for other saccadic parameters (accuracy, slope of main sequence, and peak velocity for 15 degrees saccades). These findings confirmed previous reports that saccadic parameters of MZ twins are significantly correlated and indicated that similarity of these parameters seen in MZ twins may be driven both by genetic and by prenatal environmental factors.