Canis ISSN: 2398-2942

Optic nerve head/optic disk: normal and abnormal findings

Synonym(s): Optic neuropathy, papillitis, optic neuritis

Contributor(s): Natasha Mitchell, David Gould

The normal optic disk

  • The optic disk is the optic nerve head, and it is also referred to as the optic papilla.
  • It consists of the axons of the retinal ganglion cells which course radially from the inner retina and turn at a right angle to exit the eye through a sieve-like perforation in the sclera, called the lamina cribosa.
  • Myelination begins at the optic disk, so these axons become visible at this point as they are white in color. The degree of myelination varies. With ample myelination, the disk can appear increased in size and whiter in color . A smaller, less myelinated optic disk is a normal variation .
  • The normal optic disk is almost circular in shape , but it can be more triangular or oval .
  • It is typically located near the junction of the tapetal and nontapetal regions of the fundus but this can vary depending on the extent of the tapetum .
  • There is a physiological pit near the centrer of the optic disk, which appears as a small darker area . Occasionally this is not present.
  • The retinal veins arise on the optic disk in a complete, or much more commonly, incomplete circle .
  • The disk can be sharply demarcated or it can be more indefinite, depending on the nerve fiber layer which can be medullated .
  • The peripapillary area can have a narrow zone of tapetal hyperreflectivity, termed conus, which is normal . There may be a rim of pigment around the disk, which may or may not be complete .

Congenital conditions affecting the optic disk

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Acquired conditions

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Further Reading

Publications

Refereed papers

Other sources of information

  • G J McLellan & K Narfström (2014) The Fundus. In: BSAVA Manual of Canine and Feline Ophthalmology, 3rd edn, D Gould & G McLellan (eds). Chapter 18, pp 322-356.
  • K C Barnett, J Sansom & C Heinrich (2002) Fundus. In: Canine Ophthalmology. An Atlas & Text.  Saunders. Chapter 14, pp 155-180.


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