Normally myelination of the optic nerve fibres stops when it reaches the optic disc (shortly after birth). In a proportion of people (approx. 1%) this process continues with myelination extending a variable distance into the retina.
It can be quite striking, appearing as a shiny white area of variable extent, following the line of the retinal nerve fibre layer (labelled 1 below). It is often continuous with the disc margin and has an indistinct edge.
Myelinated nerve fibres are of no significance unless the macula is involved.
This image also shows a fixation marker (labelled 2). This is an artifact on which the patient is asked to focus. The tip of the marker should highlight the fovea. Alternatively it may indicate significant maculopathy when the marker tip may be situated well away from the foveal area.