Definition
Unilateral lack of development of Optic Nerve Head.
(Optic Nerve Coloboma)

Signs
VA normal or only slightly reduced
Large disc unilaterally.  Stable, does not change over time.
Vessels emerge from disc in a radial pattern
Central portion of disc shows white glial tissue

Causes
Generally Idiopathic.  Bilateral cases are hereditary.  Rare cases show some systemic associations.

Systemic Associations
Frontonasal dysplasia - Mid-facial abnormalities.  Flat nasal bridge and/or flat midline notch on upper lid.  Pituitary deficiency, lack of a corpus callosum and basal encephalocele all possible.

Neurofibromatosis II

PHACE syndrome - in females, cardiovascular abnormalities, facial hemangiomas, and posterior fossa brain malformations.
 
No Treatment Necessary if isolated finding.  Should be a stable condition