Short-term adaptive modification of dynamic ocular accommodation.
OBJECTIVE
Indirect observations suggest that the neural control of accommodation may undergo adaptive recalibration in response to age-related biomechanical changes in the accommodative system. However, there has been no direct demonstration of such an adaptive capability. This investigation was conducted to demonstrate short-term adaptation of accommodative step response dynamics to optically induced changes in neuromuscular demands.


METHODS
Repetitive changes in accommodative effort were induced in 15 subjects (18-34 years) with a double-step adaptation paradigm wherein an initial 2-D step change in blur was followed 350 ms later by either a 2-D step increase in blur (increasing-step paradigm) or a 1.75-D step decrease in blur (decreasing-step paradigm). Peak velocity, peak acceleration, and latency of 2-D single-step test responses were assessed before and after 1.5 hours of training with these paradigms.


RESULTS
Peak velocity and peak acceleration of 2-D step responses increased after adaptation to the increasing-step paradigm (9/12 subjects), and they decreased after adaptation to the decreasing-step paradigm (4/9 subjects). Adaptive changes in peak velocity and peak acceleration generalized to responses that were smaller (1 D) and larger (3 D) than the 2-D adaptation stimulus. The magnitude of adaptation correlated poorly with the subject's age, but it was significantly negatively correlated with the preadaptation dynamics. Response latency decreased after adaptation, irrespective of the direction of adaptation.


CONCLUSIONS
Short-term adaptive changes in accommodative step response dynamics could be induced, at least in some of our subjects between 18 and 34 years, with a directional bias toward increasing rather than decreasing the dynamics.
Bharadwaj
Shrikant R
SR
Indiana University School of Optometry, Bloomington, Indiana 47405, USA. srbharad@indiana.edu
Vedamurthy
Indu
I
Schor
Clifton M
CM
D000065:Accommodation, Ocular / Q000502:physiology*; D000221:Adaptation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D006801:Humans; D009184:Mydriatics / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D010775:Photic Stimulation; D011680:Pupil / Q000187:drug effects; D055815:Young Adult
D009184:Mydriatics; D010656:Phenylephrine