Optic Nerve Hypoplasia

Optic nerve hypoplasia describes a congenital underdevelopment of the optic nerve: the nerve is smaller than normal and contains fewer nerve fibres. This leads to a visual impairment that can range from mild reduced vision through to blindness. The condition can affect one or both eyes and is one of the most common causes of unilateral or bilateral vision loss in childhood.

Causes

The exact cause of optic nerve hypoplasia is unknown in many cases. The optic nerve develops during the first months of pregnancy, and disturbances in this critical phase can lead to incomplete formation. Possible associations exist with:

• Maternal substance use during pregnancy (e.g. alcohol, certain medicines)
• Young maternal age
• Gestational diabetes
• Infections in early pregnancy

In many cases, however, no triggering factor can be identified.

Associated findings

Optic nerve hypoplasia frequently does not occur in isolation, but together with further abnormalities:

Septo-optic dysplasia (de Morsier syndrome)

A well-known combination of optic nerve hypoplasia, absence of the septum pellucidum (a thin dividing wall in the brain) and hormonal disorders of the pituitary gland. Not all three features have to be present at the same time.

Hormonal disorders

The pituitary gland (the central hormone gland in the brain) can be underactive in children with optic nerve hypoplasia. This can lead to the following problems:

• Growth hormone deficiency (delayed growth)
• Underactive thyroid
• Adrenal insufficiency (potentially life-threatening)
• Disturbances of water and salt balance (diabetes insipidus)

An early endocrinological assessment is therefore strongly recommended for every child with optic nerve hypoplasia.

Associated eye findings

• Nystagmus: involuntary eye movements, particularly where both eyes are involved
• Squinting (strabismus): common where one eye is involved or the two eyes are affected to different degrees
• Amblyopia: reduced vision that can arise in addition to the structural limitation

Diagnosis

The diagnosis is made during the ophthalmological examination:

• Back of the eye: the optic nerve head appears smaller than normal and is often surrounded by a pale ring (the so-called "double ring sign")
• OCT: measurement of the nerve fibre layer thickness confirms the thinning
• MRI of the head: assessment of the optic nerve, of the brain structures (septum pellucidum, pituitary gland) and exclusion of further malformations
• Hormone tests: blood tests to check pituitary function

Treatment

There is no treatment that addresses the cause and makes the optic nerve "grow back". Vision generally remains stable. Treatment concentrates on:

• Correction with glasses: to compensate for accompanying refractive errors
• Amblyopia therapy: where one eye is involved, occlusion treatment (patching) can improve the visual acuity of the weaker eye, provided there is still potential
• Squint treatment: prism lenses or surgery where there is a marked eye misalignment
• Hormone replacement therapy: replacing missing hormones where pituitary insufficiency has been demonstrated
• Low vision care: magnifiers, electronic magnifying aids and adapted learning materials where vision is more severely limited
• Early intervention: special programmes support motor, language and cognitive development

Long-term care

Children with optic nerve hypoplasia need long-term, interdisciplinary care from ophthalmologists, endocrinologists, paediatric neurologists and, where appropriate, other specialists. Regular check-ups make sure that hormonal disorders are detected and treated early and that the child receives the best possible support for their development.

Dr. Stefan Langenegger

Treating Ophthalmologist

044 442 04 05