title: Accommodation modulates the individual difference between objective and subjective measures of the final convergence step response.
abstract: Measuring vergence eye movements with dichoptic nonius lines (subjectively) usually leads to an overestimation of the vergence state after a step response: a subjective vergence overestimation (SVO). We tried to reduce this SVO by presenting a vergence stimulus that decoupled vergence and accommodation during the step response, i.e. reduced the degree of 'forced vergence'. In a mirror-stereoscope, we estimated convergence step responses with nonius lines presented at 1000 ms after a disparity step-stimulus and compared it to objective recordings (EyeLink II; n = 6). We presented a vertical line, a cross/rectangle stimulus and a difference-of-gaussians (DOG) pattern. For 180 min arc step stimuli, the subjective measures revealed a larger final vergence response than the objective measure; for the vertical line this SVO was 20 min arc, while it was significantly smaller for the DOG (12 min arc). For 60 min arc step-responses, no overestimation was observed. Additionally, we measured accommodation, which changed more for the DOG-pattern compared with the line-stimulus; this relative increase correlated with the corresponding relative change of SVO (r = 0.77). Both findings (i.e. no overestimation for small steps and a weaker one for the DOG-pattern) reflect lesser conflicting demand on accommodation and vergence under 'forced-vergence' viewing; consequently, sensory compensation is reduced and subjective and objective measures of vergence step responses tend to agree.
authors.affiliation: Institut für Arbeitsphysiologie an der Universitaet Dortmund, Ardeystrasse 67, D-44139 Dortmund, Germany. jainta@ifado.de
authors.forename: S
authors.initials: S
authors.lastname: Jainta
authors.forename: J
authors.initials: J
authors.lastname: Hoormann
authors.forename: W
authors.initials: W
authors.lastname: Jaschinski
mesh_terms: D000293:Adolescent; D000328:Adult; D005133:Eye Movements / Q000502:physiology*; D006801:Humans; D011237:Predictive Value of Tests; D012029:Refraction, Ocular / Q000502:physiology*; D012030:Refractive Errors / Q000175:diagnosis*; D015203:Reproducibility of Results; D015351:Vision Screening / Q000295:instrumentation*; D055815:Young Adult