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CONGENITAL ANOMALIES

Optic Nerve Hypoplasia

Optic nerve hypoplasia is the most common congenital disc anomaly observed in the pediatric ophthalmology setting. It is an outcome of errors in early intrauterine fetal development, in which abnormal pruning and/or migration of retinal ganglion axons result in a reduction in the total number of axons within the optic nerve. Fundus exam can vary but typically demonstrates a small optic disc with either normal pigmentation, grayish or pale color. The disc is often surrounded by a white or yellow peripapillary halo, which is surrounded by a second ring of pigment (double ring sign) corresponding to the size of a normal disc (Fig. 583-1). The disc may appear normal in structure with intact cup and neuroretinal rim or can appear anomalous with sectoral loss (eg, superior segmental optic nerve hypoplasia). The distance from a normal temporal disc edge to the macula is 3 disc diameters. If the optic nerve is small, the number of disc diameters increases to greater than 3.5 disc diameters. The retinal vasculature may be tortuous and/or angulated, and the optic cup may be underdeveloped. Neuroimaging often misses mild optic nerve hypoplasia. Moderate to severe optic nerve thinning suggestive of optic nerve hypoplasia can be seen, but clinical exam is needed to confirm and distinguish this from optic nerve atrophy. The diagnosis on clinical exam can be difficult if the hypoplasia is mild; disc photography and quantitative assessment of optic nerve head by optical coherence tomography (OCT) may be helpful in establishing a diagnosis.

Figure 583-1

Optic nerve hypoplasia. Arrow points to optic nerve. Surrounding hypopigmentary area (*) makes up the “double ring” sign and represents the scleral canal through which a normal-sized optic nerve would have run.

The visual acuity of an affected eye can range from normal to no light perception. The size or appearance of the optic disc does not predict the vision potential or the perseveration of an intact and functional papillomacular bundle. Optic nerve hypoplasia has been associated with fetal alcohol syndrome, maternal diabetes (usually a hemihypoplasia affecting the upper or lower half of the disc), in utero cytomegalovirus infection, toxemia, adolescent pregnancy, and maternal use of quinine, anticonvulsants, aminopterin, or illicit drugs. Accompanying ocular disorders may include aniridia, albinism, coloboma, Duane retraction syndrome, and high myopia.

Optic nerve hypoplasia can be unilateral and bilateral. With bilateral involvement, 75% of individuals have accompanying neurodevelopmental problems. In bilateral optic nerve hypoplasia, particularly in severe forms, patients may have poor vision and nystagmus early in life, as well as associated abnormalities such as mental retardation, delayed development, seizures, deafness, cerebral atrophy, hemiparesis, ventricular defects, porencephalic cyst, hypopituitarism, hypothyroidism, and diabetes insipidus. Sudden death has been reported in response to a viral illness likely due to unrecognized pituitary insufficiency. Septo-optic dysplasia, also known as de Morsier ...

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