Relative Eye Position During Monocular and Binocular Pursuit in Central Field Loss

Smooth pursuit eye movements are used to stabilize a moving stimulus on the retina. In the case of a spot stimulus the fovea closely tracks the moving target. As such, eye movements are likely conjugate during binocular tracking in the fronto-parallel plane, with the foveas of both eyes following the object of interest. Here, we investigate whether this conjugate nature is maintained in patients with central field loss (CFL), who commonly use eccentric, often non-corresponding, retinal locations during monocular viewing. Kabanarou et al. (2006) showed changes in gaze position, in CFL patients, between monocular and binocular fixation. To extend these data to when the eyes are in motion, we present eye position data (EyeLink 1000) from 7 patients and 2 controls, who performed a step ramp (Rashbass 1961) smooth pursuit paradigm at 5, 10 and 15 degrees/s. Eye movements were recorded during binocular and monocular viewing (with the non-viewing eye occluded with an infrared filter that allowed for recording). Differences in left-right eye position were computed for the duration of the trial. For all participants, the relative position of the two eyes changed between monocular and binocular viewing (ANOVA, p<0.05). However within a viewing condition, the relative positions stayed constant between the beginning and end of pursuit (t-test, p>0.2), suggesting that the same retinal location was used throughout the trial in both eyes.