The ETHAN syndrome.

Two mechanisms by which patients compensate for congenital nystagmus are assumption of a head position that places the eyes in a "null zone" of least nystagmus, known as nystagmus compensation syndrome (NCS), and convergence to dampen nystagmus, known as nystagmus blockage syndrome (NBS). We followed five patients in two groups who combine these mechanisms. The first group presented with spontaneous alternation between nystagmus and a head turn with orthotropia (NCS), and a large-angle esotropia with a variable head position that persisted even when patched (NBS). The second group of patients presented with a constant large-angle esotropia that lessened their nystagmus and variable head posture (NBS). Following recession of both medial rectus muscles with or without placement of posterior fixation sutures, they developed an abnormal head posture with orthotropia (NCS). The presence of mild amblyopia may contribute to the alternation between the two compensatory mechanisms.