MORPHOLOGICAL CONSEQUENCES OF MYELINATION IN THE HUMAN RETINA

Intraretinal myelination of ganglion cell axons occurs in about 1% of humans and when observed ophthalmoscopically, appears as a white or op aque patch within the fiber layer. Previous studies of myelinated reti nal tissue have largely been conducted at the light microscopic level. Three retinae with intraretinal myelination and one normal retina wer e obtained post-mortem and prepared for electron microscopy. The prese nt study showed that myelinated patches in the human retina contained a mixture of unmyelinated and myelinated axons. Within this population of myelinated axons were structures which were abnormal and there wer e obvious signs of axonal and myelin sheath degeneration within the my elinated patches. Outside these myelin patches the retina appeared nor mal without signs of degeneration indicating that post-mortem degenera tion prior to fixation could not account for all of the degenerative c hanges observed. The lack of significant numbers of macrophages and ly mphocytes indicated that there was no concomitant inflammatory process within the myelin patches. The myelination present within these eyes appeared to be due to the anomalous location of oligodendrocytes. Both unmyelinated and myelinated axons had larger diameters than axons mea sured within normal areas of the retina or those within the optic nerv e. (C) 1997 Academic Press Limited.