Quantitative assessment of divergence eye movements

Purpose: This study sought to quantify divergence eye movements and differences between divergence and convergence to smoothly moving ramp, step, and disappearing step stimuli. Methods: Eight visually normal, adult subjects participated in three experiments investigating the dynamics of responses using an infrared limbal eye tracker. Results: There were four primary findings: (1) a smooth tracking behavior was observed for slow ramps while the fast ramps elicited smooth tracking combined with a high-velocity, step-like behavior; (2) the high-velocity components observed in the faster ramps had a similar main sequence as divergence steps; (3) divergence dynamics to disappearing steps starting at the subject's near dissociated phoria level were similar to corresponding step responses; and (4) the high-velocity components from divergence ramps were dependent on initial vergence position, whereas the high-velocity components from convergence ramps were not. Conclusion: The results suggest a preprogrammed component is present in divergence similar to convergence; however, unlike convergence, the high-velocity components from divergence ramp responses are dependent on initial vergence position.