Nelson_Pediatric Ophthalomology, 3e

14 2 Abnormalities Affecting the Eye as a Whole

MICROPHTHALMIA M icrophthalmia is a congenital unilat eral or bilateral condition in which the globe has a reduced axial length that is at least 2 standard deviations below the mean for age. The reported incidence is estimated at 0.2 to 1.7 per 100,000. Microphthalmia is more commonly bilateral and, in these cases, is more likely to have systemic involvement. The appearance of the globe and the severity of axial length reduction define the classifica tion of microphthalmia: ● Simple or pure microphthalmia: an eye that is anatomically intact except for its short axial length. Simple microphthalmia is suspected in the presence of high hyperopia ( ≥ 8 diop ters) or microcornea. Visual loss can occur in a subset of microphthalmos associated with posterior segment abnormalities. ● Severe microphthalmia: an eye that is se verely reduced in size, with an axial length of < 10 mm at birth or < 12 mm after age 1 year and a corneal diameter of < 4 mm ( Fig. 2-4 ). The globe may be inconspicuous on clinical examination, but remnants of ocular tissue, an optic nerve, and extraocular muscles will be seen with imaging. ● Complex microphthalmia: a globe with reduced size associated with developmental ocular malformations of the anterior or poste rior segment (or both) There are two types of microphthalmos: noncolobomatous and colobomatous (micro phthalmos with cyst) ( Fig. 2-5 ). The prev alence of microphthalmia is 1.5 per 10,000 births. There is no racial or sexual predilection. Etiology Microphthalmia results from an arrest in the development at any stage during the growth of the optic vesicle. ● Environmental: prenatal exposure of alco hol, thalidomide, retinoic acid, or rubella

● Heritable: via autosomal dominant, reces sive, or X-linked inheritance ■ Multiple chromosomal abnormalities ■ Single-gene disorders causing syndromic microphthalmia (e.g., CHARGE [ c olo boma of the eye or central nervous system anomalies, h eart defects, a tresia of the choanae, r etardation of growth or devel opment, g enital or urinary defects, and e ar anomalies or deafness]; Lenz microph thalmia; Goltz, Aicardi, Walker-Warburg, and Meckel-Gruber syndromes, Norrie disease; incontinentia pigmenti) ■ Bilateral severe cases are more likely to have an identifiable genetic cause grouped into autosomal dominant ( SOX2 , OTX2 , BMP4 , PAX6 , CHD7 , and TFAP2A ), auto somal recessive ( RAX , FOXE3 , STRA6 , and SMOC1 ), or X-linked inheritance ( BCOR ). ● Unknown causes: Goldenhar syndrome; cases associated with basal encephalocele and other central nervous system anomalies Symptoms ● The extent of visual loss depends on the severity of the microphthalmos and the pres ence of related anomalies. Signs Significant variability exists, depending on the severity of the microphthalmos. ● Orbital findings ■ Small orbital rim and entrance ■ Reduced size of bony orbital cavity ■ Globe is extremely small and can be malformed. ■ Extraocular muscles are present but can be hypoplastic. ■ Lacrimal gland and ducts are present but can be hypoplastic. ■ Optic nerve can be hypoplastic. ■ Small or maldeveloped optic foramen

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