Unilateral/bilateral non-progressive underdevelopment of the optic nerve.
History:
In 1884, Magnus was the first to describe a small pale optic nerve with presence of the retinal vessels unilaterally in a small child. The child had no apparent useful vision in that eye. This case presentation was the first to completely describe all the characteristics of optic nerve hypoplasia. During the next 50 years, isolated additional 15 cases of ONH were reported.
In 1941, there was first reported association of ONH and absence of the septum pellucidum in a seven-month-old infant with congenital blindness and otherwise normal development. In 1956, de Mosier described a patient with hypoplasia of the optic nerves and agenesis of the septum pellucidum and defined this as “septo-optic dysplasia.” Within six years, he reported 36 cases of septum pellucidum agensis, nine of which had an associated ONH.
Hoyt et al. first described the association of pituitary dwarfism with septo-optic dysplasia in 1970. In 1970, Hoyt and colleagues observed that some cases of septo-optic dysplasia also had hypopituitary dwarfism; hence, the evolution of the expanded term “septo-optic-pituitary dysplasia,” the descriptor most often used now. The term “septo-optic dysplasia” is often used only for the combination of ONH and absent septum pellucidum without hypopituitarism, whereas “septo-optic-pituitary dysplasia” refers to the additional presence of hypopituitarism. In that same year, Kaplan and co-workers described six patients with ONH, midline brain defects, and pituitary dwarfism. Clark and Meyer described characteristic presentation of septo-optic-pituitary dysplasia in infancy with neonatal hypoglycemia and seizures as the chief complaint. The concept of segmental (partial or incomplete) ONH was given in the report by Schwartz in 1915. He described a patient with bilateral ONH and binasal hemianopic field defects. In 1972, Hoyt and colleagues proposed that this represented congenital retrograde axonal degeneration leading to hemihypoplasia of the optic nerves, resulting from damage to the optic tract or radiation or both.
Aetiology
Risk factors:
- Preterm birth
- Low birth weight
- Intrauterine growth restriction
- Twin-twin transfusion syndrome
- Young maternal age
- Primiparity
Associated defects:
- Ocular abnormalities (microphthalmos, aniridia, coloboma, nystagmus, and strabismus)
- Cranial abnormalities (agenesis of septum pellucidum, anenephaly, midline abnormalities of brain)
- Facial anomalies
Classification
- Type I: Optic Nerve Hypoplasia Simplex
- Diffuse
- Segmental
- Segmental with tilt
- Type II: Septo-optic dysplasia
- Type III: Septo-optic-pituitary dysplasia.
Clinical features
- Varying degree of visual acuity ranges
- ONH is a stable condition and visual function does not deteriorate with time.
Diagnosis
Ophthalmoscopy:
Diagnosis of ONH is made by ophthalmic confirmation of a small optic disc with the vasculature appearing very large relative to the disc
- Disc substance markedly reduced
- Bare area of exposed sclera surrouding optic disc
- Retinal nerve fiber layer variably thinned
- Grayish/whitish optic disc
Management
- Annual monitoring
- Refractive errors should be treated when the visual acuity reaches a functional level