Ординатура / Офтальмология / Английские материалы / Handbook of Pediatric Neuro-Ophthalmology_Wright, Spiegel, Thompson_2006

fails to account for the frequent coexistence of optic nerve hypoplasia with other CNS malformations. More recently, it has been suggested that an encephaloclastic process involving the afferent visual pathways in utero could cause direct axonal injury, leading to subsequent degeneration. The frequent association of cerebral hemispheric anomalies with optic nerve hypoplasia suggests that some cases of optic nerve hypoplasia may result from a diffuse disruption of neuronal guidance mechanisms that regulate the migration of both cerebral hemispheric neurons and optic nerve axons in utero. Toxic substances or structural abnormalities may augment the usual process by which superfluous optic nerve axons are eliminated between the 16th and 31st gestational weeks and thereby result in optic nerve hypoplasia. In some cases, optic nerve hypoplasia may occur secondary to retrograde transsynaptic degeneration of retinogeniculate axons secondary to a prenatal injury to the optic radiations.8,39,57 This mechanism may be responsible for the optic nerve cupping that occurs in children with periventricular leukomalacia.39

Clinical Assessment

The detection of hypopituitarism is an essential component of the evaluation of children with optic nerve hypoplasia because children with endocrinological deficiency are at risk for impaired growth, hypoglycemia, developmental delay, seizures, and death.11 Early pituitary hormone replacement may prevent or ameliorate these complications. Parents should be asked about protracted neonatal jaundice (which suggests hypothyroidism) and previous episodes of hypoglycemia in the neonatal period or during periods of illness (which suggest hypocortisolism).

Magnetic resonance imaging is an integral part of the diagnostic evaluation of children with optic nerve hypoplasia. Cerebral hemispheric anomalies are predictive of neurodevelopmental deficits, and neurohypophyseal abnormalities are predictive of endocrinological deficiency.12,61 Children with neurohypophyseal abnormalities or clinical signs of hypopituitarism require diagnostic endocrinological evaluation.61 Conversely, children with a normal neurohypophysis are at low risk for hypopituitarism. Parents, pediatricians, and neurologists can be informed of this potential risk, and these children can be followed for clinical signs of hypopituitarism including monitoring of their growth rate. If these children do not manifest clinical signs or symptoms of hypopituitarism, further endocrinological investigation is not warranted.61

Inheritance

Usually sporadic.

Natural History

Infants with optic nerve hypoplasia may have superimposed delayed visual maturation. Therefore, infants who initially appear to be blind may have improvement of their vision during the first several months of life. In children with unilateral or asymmetric optic nerve hypoplasia, superimposed amblyopia may further reduce vision. Children with hypopituitarism are at risk for growth retardation, developmental delay, hypoglycemia, seizures, and death.11

Treatment

Superimposed amblyopia should be treated with a trial of occlusion therapy. Children with hypopituitarism are treated with pituitary hormone replacement.

Prognosis

Occlusion therapy may improve vision in children with superimposed amblyopia. Treatment of children with endocrinological deficiency with pituitary hormone replacement should prevent or ameliorate complications of hypopituitarism noted previously.

EXCAVATED OPTIC DISC ANOMALIES

Optic disc coloboma, morning glory disc anomaly, and peripapillary staphyloma fall within the category of excavated anomalies involving the optic disc. In the latter two conditions, an excavation of the posterior globe surrounds and incorporates the optic disc. Pollock has elegantly detailed the clinical features that distinguish the excavated optic disc anomalies.63 He points out that the terms morning glory disc, optic disc coloboma, and peripapillary staphyloma are often transposed in clinical reports and review articles, which has propagated confusion about their diagnostic clinical features, associated findings, and pathogenesis. From his analysis, it is clear that optic disc colobomas, morning glory optic discs, and peripapillary staphylomas con-

FIGURE 6-5. Morning glory optic disc. The disc is large with a surrounding zone of pigmentary disturbance. The retinal vessels appear increased in number as they emerge from the disc and have an abnormally straight, radial configuration. A central glial bouquet overlies the disc. (From Pollock S. The morning glory disc anomaly: contractile movement, classification, and embryogenesis. Doc Ophthalmol 1987;65:439– 460, with permission.63)

enlarged, orange or pink in color, and typically situated within a funnel-shaped excavation (Fig. 6-5). Surrounding the excavation is a variably elevated annular zone of altered retinal pigmentation. A white tuft of glial tissue overlies the recessed central portion of the lesion. The blood vessels appear increased in number and arise from the periphery of the disc. They run an abnormally straight course over the peripapillary retina and tend to branch at acute angles. It is often difficult to distinguish arterioles from venules. The macula may be incorporated into the excavation (macular capture) (Fig. 6-6). Computed tomography (CT) scanning shows a funnel-shaped enlargement of the distal optic nerve at its junction with the globe6,50 (Fig. 6-7).

FIGURE 6-6. Morning glory optic disc. Arrow denotes focal yellowish discoloration that corresponds to macula lutea pigment (macular capture). (From Goldhammer Y, Smith JL. Optic nerve anomalies in basal encephalocele. Arch Ophthalmol 1975;93:115–118, with permission28)

Visual acuity generally ranges between 20/200 and finger counting, but cases with 20/20 vision and others with no light perception have been reported. Although most cases are unilateral, several bilateral cases with 20/20 to 20/70 vision have been reported, suggesting that functional amblyopia may be an important mechanism of visual loss in unilateral cases.6 Morning glory discs are more common in females and rare in blacks.30

Natural History

Serous retinal detachments are reported to occur in 26% to 38% of eyes with morning glory discs and usually involve the peripapillary retina.63 In addition, careful fundus examination reveals nonattachment and radial folding of the retina within

FIGURE 6-9. Optic disc coloboma. The superior disc substance is spared. The inferior aspect of the disc appears as a white excavation that merges into a retinochoroidal coloboma. (Courtesy of Dr. K. Packo)

The excavation is decentered inferiorly, so that the superior neuroretinal rim is often spared, reflecting the position of the embryonic fissure relative to the primitive epithelial papilla.63 In some instances, the entire disc is excavated, but the colobomatous nature of the defect can still be appreciated ophthalmoscopically because the excavation is deeper inferiorly. The defect may extend further inferiorly to involve the adjacent choroid and retina (Fig. 6-9), in which case microphthalmia is frequently present.26 Iris and ciliary colobomas often coexist. Histopathological examination in optic disc coloboma has demonstrated the presence of smooth muscle strands oriented concentrically around the distal optic nerve.73 This pathological finding accounts for the contractility observed clinically in rare cases of optic disc coloboma. Visual acuity may be mildly or severely decreased and is difficult to predict from the optic disc appearance. Unilateral and bilateral optic disc colobomas occur with approximately equal frequency. Magnetic resonance imaging shows hypoplasia of the ipsilateral