The pathology, clinical features, and disorders associated with optic nerve hypoplasia in children are reviewed from the Tennent Institute of Ophthalmology, Weston Infirmary, Glasgow, Scotland. A total of 100 references is provided. Histologically a reduced number of optic nerve fibers can be demonstrated in a smaller than normal optic nerve. An overgrowth of retinal pigment epithelium surrounding the small optic disc gives rise to the “double ring sign”. Failure of differentiation of the retinal ganglion cell layer between the 12 and 17 mm stages of embryonal development has been suggested as a cause of optic nerve hypoplasia (ONH). Other theories include axonal degeneration within the optic nerve or stretching of the optic nerve during the development of abnormal cerebral hemispheres. Factors predisposing to ONH include maternal diabetes mellitus, postmaturity, young maternal age, alcohol abuse during pregnancy, and maternal use of anticonvulsants, quinine, LSD, and phencyclidine. Three clinical varieties are described: 1) Isolated abnormality in an otherwise normal eye; 2) In malformed eyes; 3) With other disorders involving the midline structures of the brain. Nystagmus, poor vision, and visual field defects occur. The differentiation from optic atrophy is important and may require examination with sedation and fundus photography. The electroretinogram is normal but the amplitude of the visual evoked response is reduced. ONH occurs with 25% of cases of agenesis of the septum pellucidum and 27% of patients with ONH have partial or complete absence of the septum pellucidum. The neurological features of this condition, known as septo-optic dysplasia, include mental retardation, spasticity, abnormalities of taste and impaired smell. The ability to learn tasks requiring spatial orientation may be impaired. A number of neurological conditions may be associated with ONH and these include porencephaly, cerebral atrophy, anencephaly, hydrocephaly, congenital suprasellar tumors, and Aicardi syndrome. The frequent association of endocrine problems with ONH should alert the physician to test for pituitary dysfunction early in infancy so that optimal replacement therapy can be given. Children with septo-optic dysplasia and a deficiency of growth hormone frequently have normal growth until their third or fourth year of life. Pituitary dysfunction with ONH may be manifested as diabetes insipidus, prolonged neonatal hyperbilirubinemia, hypotonia, infantile hypoglycemia, hypothyroidism, and growth retardation. All children with ONH should have a careful neuroendocrinology exam including a CT scan. [1]