Abstract
Purpose: :
Focused and corresponding retinal images are necessary for normal visual development. Some children exhibit a bias to responding to blur or disparity when these cues are put in conflict relative to habitual viewing (Bharadwaj & Candy, 2009). The purpose of this study was to investigate the source of the bias by examining subjects’ ACA and CAC ratios.
Methods: :
Subjects from 3 months to 13 years of age, with cycloplegic SE refractive errors from -0.25 to +6D, viewed a cartoon movie placed at 80cm for all testing conditions. Cue-conflicts were introduced using -2D lenses or 2MA base-out prisms. The ACA ratio was estimated by occluding one of the subject’s eyes with an infrared filter while a -2D lens was placed in front of the other. The CAC ratio was estimated by placing a difference-of-Gaussian mask over the cartoon, to make blur uninformative, and introducing a 2MA base out prism. Vergence and accommodation responses were measured simultaneously with a video-based eccentric photorefractor (MCS PowerRefractor, 25Hz). Data collection was repeated within three weeks to provide test-retest data.
Results: :
The subjects were able to generate relative responses in the conflicting conditions. In both cases the fellow system exhibited a smaller response than predicted by the ACA or CAC ratio (p<0.001 for both ACA in the lens conflict & CAC in the prism conflict). While many subjects had no bias to blur or disparity cues, some demonstrated a repeatable bias to blur or disparity stimuli, or unstable biases. Biases or unstable behavior were not related to age or cycloplegic refractive error over the ranges tested, but increased in prevalence in the tails of the ACA and CAC distributions.
Conclusions: :
Some young children exhibit a bias to respond to blur or disparity, which is associated with the response ratios of their accommodation and vergence systems. This association between cue biases and neural coupling may be predictive of differing clinical outcomes in young patients.
Keywords: accommodation • vergence • development