Optic Nerve Hypoplasia

Also known as: Optic Nerve Head Hypoplasia

Background

Optic nerve hypoplasia (ONH) is a congenital condition (present at birth) in which there is underdevelopment of the optic nerve. ONH can be unilateral (affecting one eye) or bilateral (affecting both eyes) and occurs in both males and females. ONH is thought to be one of the three most common causes of visual impairment in children.

Credits

Medical text written October 2005 by Miss Isabelle Russell-Eggitt. Last updated October 2010 by Isabelle Russell-Eggitt, Consultant Ophthalmic Surgeon, Great Ormond Street Hospital, London, UK.

What are the symptoms?

The optic nerve carries visual information from the eye to the brain, which interprets it and allows people to ‘see’ objects and the surrounding world. This process can be interrupted to a greater or lesser degree depending on the amount of underdevelopment of the optic nerve. If the nerve in only one eye is affected in a minor way vision can be almost normal but if both eyes are affected in a more major way, the individual may only be able to see large objects and in severe cases not to see even a bright light.

Other ocular features of ONH may include:

  • nystagmus
  • mild photophobia (light sensitivity)
  • problems of peripheral vision (inability to see objects to the side of vision)
  • poor depth perception (reduced ability to judge distances).

ONH may also be associated with other conditions such as septo-optic dysplasia, which is due to incorrect development of the pituitary gland and if visual impairment is severe with disrupted sleep pattern.

What are the causes?

ONH is likely to be due to a variety of causes. The cause of most cases of ONH is not known but in a few cases there may be an association with maternal diabetes (see entry Diabetes Mellitus), maternal weight loss during pregnancy and vaginal bleeding early in pregnancy. It is believed that, at some stage of the growth of the fetus, there is a loss of nerve fibre resulting in underdevelopment of the optic nerve.

How is it diagnosed?

ONH is diagnosed on examination of the optic disc by a doctor looking into the eye with an ophthalmoscope and seeing the size of the optic nerve head. In some cases it may be difficult to be sure that the nerve is small especially if the baby is very young or very wriggly during the examination. It can be helpful to look at the size of the optic nerve behind the eye on a magnetic resonance imaging (MRI) brain scan. This examination also is helpful as other structures may be small such as the pituitary gland. Electrodiagnostic testing of the visual evoked potential (electrical signal received in the brain from the eye) can sometimes be helpful in very small children to give an idea of a child’s potential vision and prognosis.

How is it treated?

There is no cure for ONH and treatment is symptomatic for the specific difficulties it causes. This is a non-progressive condition, which means that any vision that does develop is not later lost due to ONH. Even if an infant seems to be blind, vision may still develop over the first couple of years and a programme encouraging a child to ‘fix and follow’ bright toys and lights may be helpful.

Families and teachers can help children by providing appropriately sized books and toys. Children with ONH often have to learn aspects of vision, depth and perception to allow them to play and carry out many of the ordinary activities of childhood. Families can provide important assistance by teaching activities such as using slides, climbing stairs and water play.

Ongoing assessment of a child’s needs and educational path should take place.

The Developmental Journal for babies and children with visual impairment encourages families to record and celebrate their child’s learning and development through the early years.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
Most cases of ONH occur sporadically without any other family members being affected.

Prenatal diagnosis
ONH is very rarely inherited. Prenatal diagnosis is not available. However, it is possible to image the septum pellucidum (a structure in the brain) antenatally by ultrasound. Absence of this structure may be an indicator of ONH. Obstetricians should be made aware if a previous sibling has ONH so that this can be checked carefully, although absence of the structure is not necessarily associated with ONH.

Is there support?

There is currently no support group for optic nerve hypoplasia in the UK. Cross-referrals to other entries in Contact’s directory are intended to provide relevant support for those particular features of the disorder. Organisations identified in those entries do not provide support specifically for optic nerve hypoplasia.

Families can use Contact’s freephone helpline for advice, information and, where possible, links to other families. To meet other families with disabled children, join Contact’s closed (private) Facebook group.

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