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Case of the week 55 ( May 2012 )
Nystagmus Blockage Syndrome


This 5m old infant was noticed by his parents to have inward deviation of both eyes since birth
Cyclorefraction and fundus examination were done under general anaethesia and they are found normal


 See video of this patient
 


Nystagmus Blockage Syndrome

The nystagmus blockage syndrome (NBS) denotes a particular type of nystagmus that begins in early infancy accompanied by esotropia.

NBS is characterized by a reduction of the nystagmus when esotropia increases. As the viewing eye follows a target moving laterally towards the primary position and then into abduction, the nystagmus increases and the esotropia decreases. The name "nystagmus blockage syndrome" reflects the prevalent assumption that patients block their nystagmus by adducting one eye.

The diagnosis of NBS is difficult to make because :

(1) precise and uniform diagnostic criteria are lacking

(2) similar, more common disorders, such as esotropia associated with manifest latent nystagmus (MLN), are mistaken for NBS

(3) the diagnosis usually is made by clinical observation rather than by accurate oculography.

The decrease of the nystagmus by adduction or convergence may be etiologically significant in causing esotropia and introduced the term ‘‘nystagmus blockage syndrome.’’

  This syndrome is defined as an esotropia with an onset in infancy (often preceded by nystagmus), a pseudoabducens palsy, straightening of the eyes under surgical levels of anesthesia, and the appearance of a coarse manifest nystagmus during the induction phase of anesthesia. A head turn may be elicited by covering either eye, and manifest nystagmus occurs as the fixating eye moves from adduction toward abduction.

The etiologic concept of nystagmus ‘‘blockage’’ and its relationship to infantile esotropia initially became widely accepted . In fact, many believed that most cases of infantile esotropia could be explained on the basis of this mechanism.

However, criticisms ranged from whether the blockage mechanism existed at all to the demand that the diagnosis of esotropia caused by nystagmus blockage be applied only to patients in whom an inverse relationship between the angle of esotropia and the intensity of nystagmus could actually be demonstrated.

Since manifest congenital nystagmus occurs infrequently with infantile esotropia and latent or manifest-latent nystagmus is rarely found without this condition, most cases diagnosed in the past as having the nystagmus blockage syndrome probably had infantile esotropia associated with latent or manifest-latent congenital nystagmus. In this instance there is no reason to believe that the decreased nystagmus intensity in adduction is actually caused by dampening through superimposed adduction innervation, that is, by a blockage mechanism. In fact, there is evidence to the contrary.

The differentiation of these cases from the true syndrome may, in certain instances, be complicated because patients with manifest congenital nystagmus who develop esotropia from sustained convergence may convert their manifest nystagmus waveform with onset of the esotropia to a manifest-latent nystagmus waveform. Such patients will always show an increase in the magnitude of the nystagmus with abduction of the fixating eye, which is characteristic of manifest-latent but not of manifest congenital nystagmus .

Surgery

Indications for surgery exist when the esodeviation is constant. Of various surgical approaches, a recession of both medial rectus muscles, which may be combined with

posterior fixation sutures, is advocated .

Preoperative Postoperative

 


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