Head turn in 1-eyed and normally sighted individuals during monocular viewing

To determine the incidence and magnitude of head turn in persons unilaterally enucleated at an early age and in normally sighted persons patched monocularly.

The Hospital for Sick Children, Toronto, Ontario.

Fifty-two unilaterally enucleated children and adults without nystagmus (median age, 10 years) who were enucleated at an early age (median age, 18 months) due to retinoblastoma and 28 normally sighted children and adults.

Enucleated subjects were videotaped while walking 15 m toward a camera under 2 conditions: (1) fixation relaxed (just looking at the camera) and (2) fixation forced (trying to identify a small fixation target on the camera). Control subjects were tested in the fixation forced condition only. Head turn incidence and magnitude were independently rated. Three categories of head turn were used: "obvious" (> 10 degrees), "small" (5 degrees-10 degrees), and "no" (0 degree-4 degrees).

In the fixation relaxed condition, 22 (42%) of 52 enucleated subjects exhibited head turn; when fixation was forced, the incidence increased to 25 (58%) of 43 subjects. Head turn was virtually always in the direction of the missing eye. Incidence and magnitude of head turn were unrelated to age at enucleation or number of years since enucleation. In the control group, there was no consistent finding of head turn across subjects when 1 eye was patched.

One-eyed children frequently exhibit head turn unrelated to the presence of nystagmus. The direction of the head turn is "adaptive" because occlusion by the nose in the lower contralateral field is reduced.