Visual fatigue and accommodative dynamics in asymptomatic individuals.

PURPOSE

To evaluate accommodative dynamics immediately before and after visual fatigue-inducing tasks with congruent (C) and noncongruent (NC) visual stimuli.

METHODS

Accommodative dynamics for a 2-diopter (D) step (2.5 ↔ 4.5 D) stimulus were assessed using the WAM-5500 open-field autorefractor in 10 visually normal, asymptomatic, young-adult subjects before and after C and NC tasks performed on different days in a counterbalanced manner. For the C task, subjects altered binocular fixation (50 cycles) between reduced Snellen charts at 50 and 20 cm every 3 seconds to the beat of a metronome. For the NC task, subjects performed 50 cycles of accommodative flipper (± 1.5 D) as rapidly as possible while binocularly fixating on a reduced Snellen chart at 40 cm.

RESULTS

Mean steady-state (SS) response level reflecting its accuracy was significantly (p ≤ 0.05) reduced post-NC task for both increasing (4.5-D level) and decreasing (2.5-D) accommodation. Although the SS response variability was significantly (p ≤ 0.05) increased post-NC task at the 4.5-D stimulus level, it did not change significantly (p > 0.05) for the C task. There were no significant differences between the pretask and posttask group mean initial amplitude, time constant, and peak velocity for either the C or the NC task for both increasing and decreasing accommodation.

CONCLUSIONS

The accommodative system exhibited consistent fatigue effects with respect to SS variability and response accuracy. There was no objective evidence of oculomotor learning for these specific tasks.