A case of different null zones for distance and near fixation

A compensatory head posture (CHP) is a common clinical feature of congenital motor nystagmus. It is usually caused by an eccentric null zone, which is the eye position where the nystagmus intensity (amplitude x frequency) is least. A patient adopts the posture to maximize the binocular visual acuity. Occasionally, a patient may have more than one null zone, leading to the adoption of different CHPs at various times. A 10-year-old boy with congenital motor nystagmus and orthophoria, and with good corrected vision in both eyes, presented with a face turn that had been noted since infancy. For distance fixation, he consistently adopted a left face turn due to a null zone in right gaze. For near fixation, he adopted a right face turn due to a null zone in left gaze. Eye movement recordings confirmed the different locations of the null zones for distance and near fixation. After a trial of base-out prisms to stimulate convergence, which eliminated his head posture at both positions, he underwent artificial divergence surgery. He has had a satisfactory result for 18 months after surgery with a satisfactory head posture and a well-controlled exophoria. Measures to induce convergence, with prisms and then surgery, can be an effective strategy to correct the head postures caused by two different null zones in a patient with congenital motor nystagmus.