The Small Optic Disc

What is it?

Optic disc that appears small on ophthalmoscopy
Can be monocular or binocular
Reflects congenital hypoplasia (reduced axon content)
Other forebrain anomalies may be present
Maternal diabetes is associated with a rare binocular variant called “superior segmental optic disc hypoplasia” (“topless optic discs”)

Core clinical features
- Optic disc appears to have a small diameter on ophthalmoscopy
- Trap: the normal size of the optic disc is difficult to assess by ophthalmoscopy, especially in newborns
- Inner pigment ring may surround the margin of the optic disc; an outer pigment ring may surround peripapillary retinal-choroidal atrophy (“double-ring sign”)
- Optic discs may appear “topless” and be associated with dense inferior nerve fiber bundle visual field defects in patients born to insulin-dependent mothers

Imaging features
- Small-caliber optic nerve
- Thin optic chiasm and absent septum pellucidum (de Morsier syndrome)

Look for small optic discs if forebrain or pituitary abnormalities have been found
Order brain MRI if ophthalmoscopy suggests a small optic disc
Tip: forebrain abnormalities are more likely if small optic discs are present in both eyes

Anticipate deficient growth hormone and adrenocorticotropic hormone, which create a risk of sudden death in febrile illness, especially if the pre-contrast T1 MRI sequence shows an absent or upwardly displaced “posterior pituitary bright spot”
Some patients with small optic discs will have reduced vision, but…
Trap: avoid making a judgment about visual potential in infants, as optic disc size is difficult to estimate at that age and the correlation between optic disc size and visual function is poor

Pituitary hormone deficiency is more likely if optic nerve hypoplasia is bilateral and other forebrain anomalies are present
Visual function will remain stable