DEVELOPMENT OF MYELIN IN HUMAN OPTIC-NERVE AND TRACT - A LIGHT AND ELECTRON-MICROSCOPIC STUDY

The early development of myelin in human optic nerve and tract was studied in plastic-embedded material from postmortem examinations of 18 infants and children. Specimens were examined by light and EM, and a good correlation was found between the data obtained by the 2 techniques. The characteristic lamellae of myelin were 1st seen around a few fibers of tract and intracranial optic nerve at 32 wk of gestation. By term, these myelin sheaths had become thicker, and a majority of the nerve fibers had become myelinated. In the optic nerve near the globe, myelin was 1st seen at term and virtually all fibers were myelinated by 7 mo. of age. Significant increases in sheath thickness were seen in the first 2 yr, and modest increases were found thereafter. These results are in agreement with earlier observations that, in the optic nerve, myelination proceeds from the brain toward the eye. A significant amount of myelination in the human optic nerve occurs after a full-term (40 wk) gestation, during a period of rapid postnatal visual development.