Eye movement disorders

Nystagmus

Nystagmus is an involuntary spontaneous rhythmic oscillation (jerking) of one or both eyes. It is associated with poor visual acuity. The oscillations may be in the horizontal or vertical plane or may be rotary. Vertical nystagmus is usually a sign of significant brain disease and should be referred urgently. Onset may be at any age and is associated with a range of conditions varying from relatively benign to life threatening. Nystagmus that develops within 6 months of birth may be -:

• Sensory defect, associated with a wide variety of sensory disorders and congenitally idiopathic (of no underlying cause). Visual acuity varies according to a number of factors, including the level of sensory deficit, if present. There may be a gaze direction in which nystagmus is minimal called the “null zone” which may lead to the child developing an abnormal head posture. Treatment of the nystagmus involves correction of any refractive errors and prescription of appropriate low vision aids. The child, parents and teachers should be aware of the importance of the null zone. The child should be allowed to sit in the most appropriate part of the classroom to facilitate use of the null zone and allowed to use an abnormal head posture or adaptive head oscillations as required. Most children do not require surgery but it may be used to correct any associated squint or major abnormality of head posture.
• Latent, which appears when one eye is covered, but may appear when both eyes are open if one eye has poor vision e.g. amblyopia (manifest latent nystagmus). It usually appears within the first year of life but may not be detected until much later. It is most commonly associated with early onset squint but may be associated with other conditions. True latent nystagmus is asymptomatic (without symptoms) and does not require treatment. Manifest latent nystagmus causes the child to hold the head in an abnormal position to ‘dampen’ the nystagmus and therefore requires surgical treatment to reduce the nystagmus and abnormal head posture.
• Neurological, secondary to an underlying neurological (affecting nerves) or neuromuscular (affecting nerves & muscles) disorder.