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optic nerve hypoplasia
Optic nerve hypoplasia (ONH) is a medical condition arising from the underdevelopment of the optic nerve(s). This condition is the most common congenital optic nerve anomaly. The optic disc appears abnormally small, because not all the optic nerve axons have developed properly.〔Sadun, Alfredo A., and Michelle Y. Wang. ''Handbook of Clinical Neurology''. p. 37. In press.〕 It is often associated with endocrinopathies (hormone deficiencies), developmental delay, and brain malformations. The optic nerve, which is responsible for transmitting visual signals from the retina to the brain, has approximately 1.2 million nerve fibers in the average person. In those diagnosed with ONH, however, there are noticeably fewer nerves.
==History and Epidemiology==
Optic nerve hypoplasia (ONH) is a congenital condition in which the optic nerve is underdeveloped (small).
Many times, de Morsier’s Syndrome or septo-optic dysplasia (SOD) is associated with ONH, however, it is possible to have ONH without any additional issues like SOD. SOD, is a condition that can involve multiple problems in the midline structures of the brain, stemming from miswiring of the brain and central nervous system. Besides having small optic nerves, persons with ONH can have agenesis of the corpus callosum, absence of the septum pellucidum, maldevelopment of the anterior and posterior pituitary gland, and anomalies of the hypothalamus. Because of this, all children with ONH are at risk for developmental delays and hormonal deficiencies, regardless of severity of ONH, or whether abnormalities are visible by MRI.
The incidence of ONH is increasing, although it is difficult to estimate the true prevalence. Between 1980 and 1999, the occurrences of ONH in Sweden increased four-fold to 7.2 per 100,000, while all other causes of childhood blindness had declined.〔〔Blohme, Jonas, Elisabeth Bengtsson-Stigmar, and Kristina Tornqvist. "Visually Impaired Swedish Children. Longitudinal Comparisons 1980-1999." Acta Ophthalmologica Scandinavica. 78.4 (2001) 416-20.〕 In 1997, ONH overtook retinopathy of prematurity as the single leading cause of infant blindness in Sweden, with 6.3 in every 100,000 births diagnosed with ONH. The most recent prevalence report out of England in 2006 is 10.9 per 100,000.〔〔Patel Leena, Richard McNally, Elizabeth Harrison, Christopher Lloyd, and Peter E. Clayton. "Geographical distribution of optic nerve hypoplasia and septo-optic dysplasia in Northwest England." Journal of Pediatrics. 148.1(2006) 85-88.〕
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