color atlas & synopsis of clinical ophthalmology pediatric ophthalmology (2/e): part 2

CHAPTER<br /> <br /> 7<br /> Congenital Abnormalities of<br /> the Optic Nerve<br /> Aldo Vagge and Leonard B. Nelson<br /> <br /> ■<br /> <br /> OPTIC NERVE HYPOPLASIA<br /> Optic nerve hypoplasia (ONH) is a congenital, nonprogressive developmental<br /> abnormality in which the optic nerve is smaller than usual because of reduced numbers<br /> of retinal ganglion cells. It is frequently associated with other central nervous system<br /> (CNS) abnormalities.<br /> ONH may be unilateral or bilateral (80%) and may be asymmetric.<br /> Most common congenital optic disc anomaly<br /> Optic nerve aplasia is rare. No pupillary light reflex and absence of the optic disc,<br /> nerve fiber layer, and retinal blood vessels on examination.<br /> Etiology<br /> Not completely understood<br /> Parental drug and alcohol abuse contributes to an increasing prevalence of ONH.<br /> Drug associations include exposure to carbemazepine, isotretinoin, phenytoin, quinine,<br /> and valproic acid. Young maternal age and maternal insulin-dependent diabetes have<br /> also been implicated in some cases (associated with subtype—superior segmental optic<br /> hypoplasia).<br /> Genetics<br /> Most cases are sporadic.<br /> <br /> Bilateral ONH is inherited in an autosomal-dominant pattern based on the few<br /> families reported. Mutation in the PAX6 (11q13) gene is responsible.<br /> Mutation in the HESX1 gene has been identified in sporadic septo-opto dysplasia<br /> and pituitary disease.<br /> Mutation in the TUBA8 gene is associated with polymicrogyria and ONH.<br /> Symptoms<br /> Decreased vision in one or both eyes<br /> Strabismus may be associated with unilateral ONH.<br /> Signs<br /> Range of visual acuity is 20/20 to no light perception since vision is determined<br /> primarily by the integrity of the papillomacular nerve fibers more than the overall size<br /> of the disc.<br /> Amblyopia as a result of accompanying strabismus and anisometropia<br /> Nystagmus: often develops at 1 to 3 months of age in bilateral cases<br /> Strabismus may be associated with unilateral ONH.<br /> Afferent pupil defect in asymmetric or unilateral cases<br /> Visual fields (VFs) often have localized defects as well as general constriction.<br /> Abnormally small optic nerve head, often gray or pale in color with “double-ring<br /> sign” (scleral canal surrounds a small optic nerve) (Fig. 7-1)<br /> Superior segmental hypoplasia of the optic nerve is a segmental form of ONH<br /> occurring in some children of insulin-dependent diabetic mother.<br /> Retinal vascular tortuosity is common.<br /> Associated Conditions<br /> Septa-optic dysplasia: combination of small anterior visual pathways, absence of the<br /> septum pellucid, and thinning or agenesis of the corpus callosum<br /> Endocrine dysfunction: pituitary gland abnormalities in approximately 15% of<br /> patients with ONH. Patients are at risk for hypothalamic and pituitary dysfunction such<br /> as growth hormone deficiency (most common), hypothyroidism, hyperprolactinemia,<br /> panhypopituitarism, and diabetes insipidus.<br /> Cerebral anomalies such as error in hemispheric migration (schizencephaly, cortical<br /> heterotopias) or hemispheric injury (periventricular leukomalacia [PVL],<br /> <br /> encephalomalacia). PVL can be associated with another form of ONH characterized by<br /> large optic cups and a thin neuroretinal rim contained within normal-sized optic discs.<br /> This occurs secondary to trans-synaptic degeneration of optic axons caused by bilateral<br /> lesions in the optic radiations.<br /> Developmental delay more common in patients with bilateral ONH, highly<br /> correlated with corpus callosum hypoplasia and hypothyroidism<br /> Diagnostic Evaluation<br /> Magnetic resonance imaging (MRI) to rule out CNS malformations<br /> Refer to a pediatric endocrinologist if patients show clinical signs of endocrine<br /> dysfunction or pituitary abnormalities on MRI. Pediatrician should follow growth chart<br /> for endocrine changes. Undiagnosed endocrine deficiencies are at risk for impaired<br /> growth, hypoglycemia, seizures, and death.<br /> Automated VF testing may be useful but children are often too young to cooperate.<br /> Differential Diagnosis<br /> Optic atrophy<br /> Optic nerve coloboma<br /> Ocular albinism<br /> Treatment<br /> No treatment available to improve the vision in ONH<br /> Correction of refractive errors<br /> Treatment for superimposed amblyopia<br /> Surgery for concurrent strabismus or nystagmus may be considered.<br /> Consider polycarbonate eye glasses for protection of the better-seeing eye.<br /> Prognosis<br /> Visual acuity is generally nonprogressive. Complications are in general related to<br /> endocrinopathies and CNS malformations.<br /> <br /> FIGURE 7-1. Optic nerve hypoplasia. Note the double-ring sign.<br /> <br /> MORNING GLORY DISC ANOMALY<br /> Morning glory disc anomaly (MGDA) is a rare, congenital, usually unilateral funnellike excavation of the posterior fundus that incorporates the optic disc.<br /> The name derives from the similarity to the morning glory flower.<br /> More common in female and rare in African Americans.<br /> Etiology<br /> The embryologic basic of MGDA is unclear. A defect in fetal fissure closure or a<br /> primary mesenchymal abnormality has been hypothesized as embryonic origins of<br /> morning glory anomaly.<br /> Symptoms<br /> Decreased vision most common in the involved eye<br /> Color vision defect<br /> Signs<br /> <br /> Visual acuity can range from normal vision to no light perception but in general is<br /> approximately 20/100 to 20/200.<br /> Strabismus<br /> Leucokoria<br /> Amblyopia<br /> Myopia<br /> Afferent pupil defect<br /> VF defects, commonly enlarged blind spots<br /> The optic disc is markedly enlarged, orange or pink in color, with a surrounding<br /> annular ring of pigmented uveal tissues. Retinal vessels increased in number emanate<br /> radially from the disc, a central white tuft of glial tissue. Macula may be incorporated<br /> into the excavation (macular capture) (Fig. 7-2).<br /> Serous retinal detachment (RD) in one-third of patients<br /> Associated Conditions<br /> Trans-sphenoidal basal encephalocele associated with midfacial anomalies<br /> (hypertelorism, flat nasal bridge, midline notch in the upper lip, and sometimes a<br /> midline cleft in the soft palate).<br /> Midline or other brain abnormalities (e.g., agenesis of the corpus callosum, pituitary<br /> abnormalities)<br /> Ipsilateral abnormalities of the carotid circulation such as stenosis or aplasia of the<br /> carotid arteries with or without Moyamoya syndrome (progressive stenosis of the<br /> terminal portion of the internal carotid artery and its main branches)<br /> Associated with ipsilateral orofacial hemangioma—this association may fall within<br /> the spectrum of the PHACE syndrome (posterior fossa malformation, large facial<br /> hemangioma, arterial anomalies, cardiac anomalies and aortic coarctation, and eye<br /> anomalies)<br /> Associated with neurofibromatosis type 2<br /> MGDA has been described as part of the spectrum of renal coloboma syndrome.<br /> Diagnostic Evaluation<br /> MRI and magnetic resonance angiography should be obtained to rule out brain and<br /> vascular abnormalities.<br /> Rule out endocrine dysfunction (thyroid-stimulating hormone and growth hormone<br /> <br />