Nelson_Pediatric Ophthalomology, 3e

20 2 Abnormalities Affecting the Eye as a Whole

TYPICAL COLOBOMA T he term coloboma is derived from the Greek koloboma , meaning mutilated or curtailed. It is a congenital malformation and refers to a notch, gap, hole, or fissure in any of the ocular structures. Typical colobomas are frequently bilateral and are often associated with microphthalmia. Etiology ● “Typical” colobomata are caused by defec tive closure of the optic fissure during the fifth to seventh weeks of fetal life and because of the location of the fetal fissure and are found in the inferonasal quadrant in the eye. SHH , PAX2 , PAX6 , and VAX genes have been impli cated in optic fissure formation and closure. However, not all patients with mutations in these genes develop coloboma. (“Atypical” colobomata are less frequent malformations located outside the inferotemporal quadrant, for which the etiology is still unclear.) ● Most cases are idiopathic and sporadic, but all types of inheritance (i.e., autosomal dominant, autosomal recessive, and X-linked) have been reported and may be associated with various syndromes, such as CHARGE, Meckel-Gruber, Lenz microphthalmia, Aicardi, Patau, and Edwards syndromes. The preva lence of coloboma is 0.7 per 10,000 births. Signs ● Ocular colobomata may affect any of the structures or the entire globe traversed by the fetal fissure from the iris to the optic nerve. It has a variable appearance, depending on the extent and severity of the coloboma. ■ Iris: Complete iris coloboma presents as an inferonasal defect merging with the pupil seen as a “teardrop” pupil ( Fig. 2-9A ). Par tial iris coloboma can be seen as heterochro mia iridis, defects in the pigment epithelium, or transillumination defects. ■ Lens: inferior anomalies including ab normal shape/defect, flattening of lens or absence of lens zonules

■ Leukocoria: if the uveal defect is large ■ Optic nerve: enlarged, excavated, vertically oval; retinal vessels may radiate in a spoke like manner from the nerve ( Fig. 2-9B ). ■ Chorioretina: thinning of the choriocapil laris; pigment clumping along the line of op tic fissure closure; the colobomatous defect usually has sharp edges and is circumscribed by irregular pigmentation; a white sclera is seen through the defect if all layers of the chorioretina are absent; the floor of the de fect sometimes bulges, forming a staphyloma ( Figs. 2-9C to 2-9F ). ■ Globe: microphthalmia in some cases ■ Vision: ranges from normal to no light perception ● May be associated with a variety of other developmental defects Differential Diagnosis ● Atypical coloboma ● Retinal toxoplasmosis ● Optic nerve pits

● Morning glory syndrome ● Optic nerve hypoplasia Diagnostic Evaluation ● Clinical examination of the eye Treatment

● Glasses may be needed for any significant refractive error, which is frequently myopic. ● With optic nerve involvement, if unilateral, or bilateral and asymmetric, or with anisometro pia, patching for amblyopia may be necessary to stimulate as much potential vision as possible. ● Treat ocular complications: cataract, sub retinal neovascularization, and retinal breaks

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or detachment Prognosis

● Vision depends on involvement of the optic nerve, macula, and papulomacular bundle. However, visual acuity cannot be predicted