Visual pathway disorders
Acquired disorders of the optic nerve
Congenital disorders of the optic nerve
Disorders of the posterior visual pathways
Acquired disorders of the optic nerve
Papilloedema is swelling of the head of the optic nerve. It is usually due to raised intracranial (within the skull) pressure, secondary to, for example, brain tumours although other causes such as high blood pressure are possible. It does not usually cause significant visual problems and treatment is directed to the underlying cause.
Acquired optic atrophy is degeneration of the nerve fibres within the optic nerve. There are several possible underlying causes, including raised intracranial (within the skull) pressure (e.g. due to hydrocephalus, brain tumour), compression of the optic nerve, trauma, optic neuritis and metabolic disorders. It may cause reduced visual acuity and squint. Treatment is directed to the underlying cause.
Optic neuritis is an inflammation of the optic nerve. Unilateral (affecting one eye) optic neuritis is associated with virus infections and toxoplasmosis, bilateral (affecting both eyes) optic neuritis is usually of unknown cause but in teenagers, may be associated with multiple sclerosis. Optic neuritis usually presents with a sudden onset of eye pain and visual loss. It may be treated with systemic steroids to speed up the resolution of symptoms. There is usually good recovery of visual acuity.
Optic nerve glioma is a tumour that affects the optic nerve. They are more common in children with Neurofibromatosis (a genetic disease causing multiple soft tumours under the skin) type 1 (NF1) but may occur sporadically in the absence of NF1. Children may present with a bulging eye (proptosis) or squint but may be asymptomatic (without symptoms) and visual acuity is usually well preserved. In children with NF1 they tend to be relatively benign and may regress spontaneously but in sporadic cases where there is rapid growth or vision is affected, they should be surgically removed.
Trauma from a head injury may result in damage to the optic nerve. Shaking in non-accidental injury may cause retinal haemorrhages, bleeding into the optic nerve and damage to the visual cortex, thereby affecting visual acuity.
Disorders of the visual pathway affect the optic nerve and its communications with the area of the brain responsible for vision, the visual cortex. They result in visual loss but usually without other visual symptoms. Younger children rarely complain of unilateral loss of vision and bilateral visual loss may not be symptomatic until it is very advanced.
Congenital (present at birth) disorders of the optic nerve
Optic nerve hypoplasia (ONH) is an uncommon condition where there is underdevelopment of the optic nerve. Bilateral cases may result in severe visual impairment and nystagmus (jerky eye movements) in infancy. Unilateral cases may be less severe and result in visual field defects and squint. ONH may be associated with brain abnormalities especially with defects in the pituitary gland and cause problems in growth. ONH may be caused by alcohol and drug abuse during pregnancy (Foetal Alcohol Syndrome).
Optic nerve coloboma (a cleft like defect) may affect the optic nerve alone or the iris and retina as well. The severity of visual loss is determined by whether the macula (central retina) is affected and by the severity of the optic nerve abnormality. It is associated with an increased risk of retinal detachment. There is no specific treatment for the coloboma (cleft-like defect) but treatment of any refractive error and amblyopia (lazy eye) is required.
Optic disc dysplasia is a condition where there is abnormal development of the optic nerve. The child usually presents with a squint due to a refractive error and astigmatism. It is associated with an increased risk of retinal detachment. In most children, vision is good and management involves correcting any refractive error and treating amblyopia if present.
Congenital optic atrophy is a condition where the optic nerves are normal size but there has been degeneration of the nerve fibres within the optic nerve during pregnancy. Children with congenital (present at birth) optic atrophy usually have multiple neurological and developmental problems. The prognosis for visual acuity varies widely.
Disorders of the optic chiasm
The optic chiasm is the place where the optic nerves meet and crossover behind the eyes. A variety of disorders may affect the optic chiasm, including developmental defects, tumours, inflammation and trauma. They may present in infancy as blindness, poor visual acuity and nystagmus or with progressive visual failure later in childhood. Visual acuity is often severely reduced at presentation and colour vision is also often affected. Treatment, if possible, is directed towards the underlying cause.
Disorders of the posterior visual pathways
Disorders of the visual pathway after the optic chiasm, including the visual cortex are often associated with other developmental and neurological problems. They may have several causes that include developmental defects, trauma or tumours. Children may present in infancy with poor fixation, squint and abnormal eye movements. Visual function will depend upon the nature and extent of the underlying pathology. Children with disorders of the visual cortex often demonstrate improvement in visual function over a period of time.
Delayed visual maturation is a condition where an infant is noticed to have no eye contact or visual interest in the first six to eight weeks of life. No underlying cause for visual loss is found and spontaneous improvement in vision occurs at about twelve to fifteen weeks of age so that vision is eventually normal.
There is usually no specific treatment for children with visual pathways disorders. The extent of any visual deficiency may not be fully appreciated until the child starts school. Regular follow up is required, together with correction of any refractive errors, provision of low visual aids, the management of amblyopia and surgical correction of unsightly squint.
