Background and Aims Thyroid hormones have an important role throughout prenatal and postnatal nervous system development. They are involved in several processes such as neurogenesis, gliogenesis, myelination, as shown in many cases of deficiency like CI. Some could be reversed after adequate supplementation of thyroid hormones at birth, however there are other cellular processes highly sensitive to low levels of thyroid hormones and lasting a limited period of time during which if thyroid hormone action is lacking or deficient, the functional and structural damages would produce permanent defects. Visual system is particular vulnerable to thyroid hormones and for this reason we decided to study children with CI early treated by means of visual motion tasks to evaluate basic and high level functions.
Methods and results: Ten children with early treated CI and ten controls matched for sex and age and Intelligence Quotient were enrolled in the study. We found no differences in basic visual functions. Motion perception was assessed by two alternative forced choise of direction of motion for different levels of noise corruption displayed on the screen for a limited lifetime. Three types of coherent motion were studied: rotational, radial and translational motion. We found a statistical difference in the thresholds for radial motion.
Conclusions Our results seem to confirm that CI can influence the development of the visual dorsal stream, a pathway particularly vulnerable during the last three months of intrauterine life.