IN-vision

Early-onset nystagmus describes any form of nystagmus that presents within the first few months of life, unless precipitated by a condition causing acquired nystagmus within that time. The three most common forms are:

1. Infantile nystagmus syndrome (dedicated page)
2. Fusional maldevelopment nystagmus syndrome
3. Spasmus nutans syndrome

Early-onset nystagmus is usually primarily horizontal in direction, although vertical or torsional movement can also be exhibited, either as a major or secondary component to the movement.

A recent study identified early-onset nystagmus in 0.35% of a sample of 2,546 pre-school children (Repka et al. 2012).

Infantile nystagmus syndrome

Infantile nystagmus syndrome (INS) is a permanent, non-progressive condition causing involuntary oscillations of the eyes. It first appears within the first six months of life and is often associated with a congenital pathology of the visual system. In many cases however, no defect of the visual system can be found, in which case it is classified as ‘idiopathic’ INS. The oscillations in INS are usually conjugate (the same in both eyes) and horizontal in all directions of gaze. There is usually a particular direction of gaze in which the oscillations are at a minimum; this angle of gaze is known as the null zone. Over time, an abnormal head position may develop in order to use the better vision offered by this position.

Other factors are also known to affect the INS oscillations: relaxation, convergence and closing the eyes all tend to reduce the nystagmus intensity. Conversely, stress and tiredness will usually result in an increase in intensity. The inheritance of INS is governed by the type of inheritance shown by the sensory defect that has caused the nystagmus. In the case of idiopathic INS, inheritance can be autosomal dominant, but other forms of inheritance are known to occur.

Fusion maldevelopment nystagmus syndrome

Formerly known as ‘latent nystagmus’, fusion maldevelopment nystagmus syndrome (FMNS), is perhaps the most commonly seen form of pathological nystagmus, due to the fact that its onset often follows an infantile strabismus (squint). FMNS oscillations are conjugate (the same in both eyes) and display a jerk waveform with decelerating slow phases. The oscillations beat towards the fixing eye (more accurately, the eye that the subject believes they are fixing with). The oscillation intensity increases with abduction of the fixing eye (looking outwards) and decreases with adduction of the fixing eye (looking inwards). A head turn may be adopted in the direction of the fixing eye as the reduced nystagmus intensity in this position allows better vision. FMNS can be manifest or latent (see classification).

Spasmus nutans syndrome

Spasmus nutans syndrome is a rare disorder, which causes (in combination): a high frequency, low amplitude nystagmus of a disconjugate nature, irregular head nodding and an AHP. Its onset is usually within the first year of life and the condition ceases spontaneously, usually within two years of onset, although it has been known to persist for over eight years. A low-amplitude nystagmus (not detectable clinically) may persist until at least five to twelve years of age (Gottlob et al. 1995). The pathogenesis of spasmus nutans syndrome is unknown (Leigh and Zee 2006).