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A. M. Horwood, P. M. Riddell; The Development of Infant Responses to Disparity, Blur and Proximity. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3817.
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© ARVO (1962-2015); The Authors (2016-present)
In adults, disparity is considered a major cue to both vergence and accommodation, but infants are not thought to be able to use binocular disparity until 3-4 months of age. In addition, low acuity, poor contrast sensitivity and common refractive errors may make blur an unreliable near cue in infancy, so weighting of cue use and response is likely to change with age. Our laboratory has been exploring the development of infant accommodation and vergence responses to the 3 main near cues of disparity, blur and proximity over the first six months of life in comparison to adult responses.
14 infants were tested at 2 months, 23 at 4 months and 24 at 6 months of age and were compared with 32 young adults naïve to vision experiments. No infant was >+1.75D hyperopic. Testing used a remote haploscopic off-axis videorefractor which measured simultaneous accommodation and vergence (in dioptres and metre angles) to a detailed picture stimulus at 4 positions between 0.3m and 2m. Blur, disparity and looming cues were removed selectively by using a DOG patch target, remote occlusion, or scaled targets respectively. Each participant was tested in all 4 conditions.
In the all cue condition, both vergence and accommodation were broadly appropriate for the target distance by 2 months. Vergence gain was 0.9 at 2 months and reached adult levels by 4 months (p<0.000). Accommodation gain decreased with age (p<0.000) from 1.2 & 1.4 at 2&4 months respectively to 0.9 in the adults. Maximum disruption of responses by removal of a single cue occurred in the youngest infants. In all participants, vergence gain reduced if a cue was removed (p<0.008 in all cases). In infants of all ages there were no significant differences in vergence or accommodation gain whichever cue was removed, while in the adults gain reduced markedly when disparity was removed in comparison to blur or proximity (p<0.000 in both cases). All adult responses were less disrupted by the removal of a cue as long as disparity cues were available.
Infant vergence reaches adult levels by 4 months of age. There is frequent over-accommodation for near which reduces with age, compared with adult under-accommodation. Infant vergence and accommodation responses are less affected by selective removal of disparity cues than adults’, suggesting adults rely more heavily on disparity cues than infants.
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