The development of human fetal eye movement patterns.

The eye can be visualized ultrasonically in more than 90 percent of fetuses 16 through 42 weeks of gestational age. Slow eye movements are present by 16 weeks. Rapid eye movements begin at 23 weeks and become more frequent between 24 and 35 weeks. Eye inactivity becomes more common after 36 weeks and is associated with sustained diaphragmatic excursions implying a "quiet sleep" state. Pathologic eye movements were seen in four fetuses with dysmorphic brain structure.