A number of minor congenital abnormalities are seen on the disc. In an astigmatic eye, the disc is often oval. The central cup might be filled in by "drusen" - small hyaline deposits, which can be found on the surface or buried in the substance of the disc. This appearance can mimic papilloedema. Alternatively, the central cup might be hollowed out further by a congenital pit in the disc. Myelinated retinal nerve fibres are recognised by their strikingly white appearance, which obscures any underlying vessels, and their fluffy margin (see Figure 22.3). The central cup can be filled in by persistent remnants of the hyaloid artery (Bergmeister's papilla), which runs in the embryo from disc to lens. Some of these and other congenital abnormalities of the disc can be associated with visual field defects that are not progressive but which can cause diagnostic confusion.
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