Inherited or Congenital Optic Nerve Diseases

Abstract

In this chapter, we discuss inherited/congenital optic nerve diseases and their related visual fields defects. It is important for the ophthalmologist to establish, on the basis of the visual fields defect whether the optic nerve is involved and, if so, whether this is at the level of the optic disc or further back. In addition, the visual fields defect can help establish whether the etiology is acquired or congenital. If the former is the case, then the visual fields defect may reveal an insult that is rapidly progressive and hence requires immediate and aggressive management. The diseases are divided into the categories of congenital optic disc anomalies and heredodegenerative optic atrophies. Congenital optic disc anomalies include aplasias, dysplasias (hyperplasia and hypoplasia), optic nerve colobomas and pits, anomalous disc elevations: pseudopapilledema with or without hyaline bodies (drusen), and tilted disc and crescents. Absence of the optic disc (aplasia) is extremely rare and only a few case reports have been published in the literature. Optic disc size varies and may be larger (hyperplasia) or smaller (hypoplasia) than normal. Hyperplasia is much less common than hypoplasia and is usually related to ametropias. Optic nerve hypoplasia (ONH) may be unilateral or bilateral and isolated or associated with different syndromes. It may be associated with good or poor visual prognosis. It is the most common congenital optic disc anomaly encountered in pediatric ophthalmic practice. When the nerve head is slightly or segmentally reduced, especially in the presence of normal visual acuity, the diagnosis is based on comparison of disc photographs or calculation of the ratio of the disc center-to-fovea distance to disc diameter. Usually this ratio is increased in hypoplasia and, if higher than 3.0, is almost diagnostic. Sometimes the hypoplastic disc is surrounded by a ring of sclera and a ring of hyperpigmentation, described as “double-ring sign”. Maternal diabetes and use of teratogenic agents such as phenytoin, alcohol, quinine, and cocaine may be associated with ONH.