Nelson_Pediatric Ophthalomology, 3e

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Abnormalities Affecting the Eye as a Whole 2 ■ Judith B. Lavrich and Karen E. Lee

ANOPHTHALMIA A nophthalmia , also known as anophthal mos, is a congenital anomaly that is char acterized by the complete absence of ocular tissue within the orbit. It is a leading cause of congenital blindness. Anophthalmia has a prev alence of 0.18 per 10,000 births and has no ra cial or sexual predilection. The majority of cases are bilateral, reported between 53% and 71%. Classification depends on the stage at which failure of development occurs: ● Primary or true anophthalmia is a very rare condition with complete absence of the lens, optic nerves, and chiasma due to failure of formation of the optic pit and outgrowths from the forebrain. ● Secondary anophthalmia occurs when de velopment of the eye begins but gets arrested due to an insult during development in utero, resulting in only residual eye tissue or ex treme microphthalmos. ● Degenerative anophthalmia occurs due to lack of blood supply or other causes leading to formation of the optic vesicle but subsequent halt in growth.

Etiology During embryogenesis, there is an arrest in the development of the neuroectoderm of the pri mary optic vesicle, which stems from the ante rior neural plate of the neural tube. Anophthalmia is most frequently idio pathic and sporadic but can be inherited as a dominant, recessive, or sex-linked trait. It is associated with maternal infections during pregnancy (e.g., toxoplasmosis, ru bella, cytomegalovirus, and varicella) as well as syndromes with craniofacial mal formations (e.g., Goldenhar, Hallermann- Streiff, and Waardenburg syndromes). Non infectious causes such as maternal vitamin A deficiency, exposure to x-rays during gesta tion, abuse of solvent inhalers, and toxicity from thalidomide, warfarin, and alcohol have also been postulated. It is linked with genetic defects, including trisomies 13, 14, and 15; chromosomal deletion in band 14q22-23, also known as Frias syndrome, which is character ized by anophthalmia associated with pitu itary and hand/foot abnormalities. There are multiple gene mutations that can result in anophthalmia. SOX2 is the most com mon, accounting for up to 40% of all cases.

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