Optic nerve head

The optic nerve head is the point at which the nerve fibres from the retina merge to form the optic nerve.

It is one of the only places in the body where the nervous system can be non-invasively visualised.

The optic nerve head is responsible for the blind spot.

Signs of nerve dysfunction include:

• falling acuity
• impaired colour
• relative pupil defect
• field defect

When examining the optic disc, the examiner should be aware of:

• the colour of the disc - normal colour is pale pink; the disc colour is more pallid in optic atrophy
• contour:
  • assess the disc margins - these may be blurred in papilloedema and optic neuritis
  • optic disc may seem abnormally large in myopic eyes; also may seem oval in astigmatic eyes
  • examine blood vessels - these radiate away from the optic disc; there is a normal arterial/venous width ratio of 2:3 - venous engorgement occurs in retinal vein thrombosis
• cup:
  • examine the cup of the optic disc - a physiological cup occurs centrally and occupies approximately 1/3 of the disc diameter. Deepening and widening of the cup occurs in glaucoma