Walsh & Hoyt: Myelinated (Medullated) Nerve Fibers

Myelination of the anterior visual system begins centrally at the lateral geniculate body at 5 months of gestation. It proceeds distally and reaches the chiasm by 67 months of gestation, the retrobulbar optic nerve by 8 months, and the lamina cribrosa at term; although in some cases myelination may continue for a short time after birth. Normally, myelin does not extend intraocularly; however, intraocular myelination of retinal nerve fibers occurs in 0.30.6% of the population by ophthalmoscopy and in 1% by postmortem examinations. Straatsma et al. studied both eyes from 3,968 consecutive autopsy cases and found 37 eyes from 32 patients with myelinated retinal nerve fibers. In this series, males and females were equally affected, and in most eyes, myelination was continuous with the optic disc.