Optic nerve hypoplasia

Optic nerve hypoplasia, unilateral or bilateral, is characterized by a decreased number of nerve fibers. Optic nerve hypoplasia may be an isolated anomaly, associated with other ocular malformations, or a heterogeneous group of disorders most often affecting the midline structures of the brain. Specific maternal substances that may be associated with optic nerve hypoplasia during pregnancy include alcohol, LSD, quinine, protamine zinc citrate, steroids, diuretics, cold medications, and anticonvulsants. Superior segmental hypoplasia may be associated with gestational diabetes.

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Symptoms of Optic Nerve Hypoplasia

• Visual acuity can vary from normal to blindness.
• The disc is small and gray, surrounded by a yellow halo of hypopigmentation due to concentric chorioretinal atrophy (the "double ring" sign). The outer ring represents what would be the edge of a normal disc.
• The distance from the fovea to the temporal border of the disc is often equal to or greater than three disc diameters. This indicates disc hypoplasia.
• Despite the small disc, the retinal vessels are of normal caliber but may be tortuous.
• In some cases, only part of the disc is hypoplastic.

Other manifestations vary considerably in severity and include visual field defects, dyschromatopsia, afferent pupillary defect, foveal hypoplasia, aniridia, microphthalmos, strabismus, and nystagmus in severe bilateral cases. Mild cases may go unnoticed, and slight decreases in visual acuity may be mistaken for amblyopia and treated with occlusion.

Systemic manifestations of optic nerve hypoplasia

De Morsier syndrome (retino-optic dysplasia) occurs in 10% of cases. In addition to bilateral optic nerve hypoplasia, it is characterized by malformations of the midline structures of the brain, which may be combined with endocrine disorders. These malformations include the absence or dysgenesis of the septum pellucidum, thinning or agenesis of the corpus caflosum, and dysplasia of the anterior third of the ventricle. Hypopituitarism with low growth hormone levels is common; with early diagnosis, the deficiency can be corrected with continuation of normal growth. This means that retinal vein tortuosity in patients with bilateral optic nerve hypoplasia may be a marker of potential endocrine dysfunction.

Frontonasal dysplasia is rare.

Aicardi syndrome

Aicardi syndrome is a very rare autosomal dominant X-linked disorder that is fatal to males in litem. The eye lesions are usually bilateral but are often asymmetrical.

Symptoms

• Pathognomonic are multiple depigmented chorioretinal lacunae grouped around the disc.
• Congenital disc anomalies include coloboma, hypoplasia, and pigmentation.
• Other ocular manifestations: microphthalmos, persistent pupillary membranes, cataracts, iris colobomas.
• Systemic manifestations include infantile spasm, agenesis of the corpus callosum, skeletal malformations, and psychomotor retardation. Other serious CNS malformations may be present, and death usually occurs within the first few years of life.

Other anomalies

Various rare anomalies of the optic disc, sometimes with associated neurological manifestations.

1. Megalopapilla, in which the horizontal and vertical diameters of the disc are 2.1 mm or more.
2. Parapapillary staphyloma is a non-hereditary, usually unilateral condition in which a relatively normal disc is located at the base of a deep excavation whose walls have degenerative changes, as have the surrounding choroid and retinal pigment epithelium. Visual acuity is reduced; there may be focal retinal detachment and, occasionally, frontonasal dysplasia.
3. Optic disc dysplasia is a descriptive term for a deformed disc that does not fit into any diagnostic category.