Cyclotorsion: a possible cause of residual astigmatism in refractive surgery.

Purpose: To determine whether cyclotorsion occurs when a subject changes from binocular to monocular fixation and to assess positionally induced cyclotorsion.

Setting: Clinics of the Rotterdam Eye Hospital, Rotterdam, The Netherlands.

Methods: The axis of astigmatism was measured with the Nidek handheld keratometer in 15 normal subjects under monocular and binocular fixation and in seated and supine positions.