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Shrikant Bharadwaj, Rowan Candy; Accommodative and vergence responses to conflicting blur and disparity cues in the developing visual system. Journal of Vision 2008;8(6):798. doi: 10.1167/8.6.798.
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© ARVO (1962-2015); The Authors (2016-present)
Adults achieve clear and single visual experience using accommodation and vergence. While these systems are already coupled in early infancy very little is known about their interaction during development, even though it is implicated in forms of strabismus and is central to three-dimensional space perception. Here, we assessed the interaction under two conditions, i) where cues to accommodation and vergence (blur and disparity) were consistent with each other and ii) where these cues were in conflict with each other. Subjects from 4 months to 12 yrs of age viewed a high contrast cartoon binocularly while their accommodative and vergence responses were measured at 25Hz using photorefraction (PowerRefractor). In the cue-consistent condition, the target was physically moved between 80 and 31 cms (2D or MA). In the cue-conflict conditions, either −2D lenses or 2MA base-out prisms were placed before the eyes, with the target at 80 cms. The data revealed three characteristics. First, while subjects always responded in the cue-consistent condition, they responded more frequently to the prisms (mean 83.6% of trials) than to the lenses (60.5%) in cue-conflicting conditions. Second, the gains of both direct and coupled responses were smaller to lenses (accommodation: 0.55 +/− 0.25; vergence: 0.14 +/− 0.09) than to prisms (vergence: 0.69 +/− 0.37; accommodation: 0.30 +/− 0.11) [both p+ 0.18; vergence: 1.13 ± 0.14) [both p[[lt]]0.001]. Third, the ratio of vergence to accommodation gain for the lenses was less than and poorly correlated with the subject's AC/A ratio (p[[lt]]0.01; r=0.08). Overall, these results indicate that the developing visual system responds to 2D or MA cue-conflicts by attempting to minimize both retinal blur and disparity, with some bias towards keeping the visual experience single rather than focused.
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