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S. R. Bharadwaj, T. R. Candy; Characteristics of Pupil Responses During Human Visual Development. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1836.
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Pupil size plays an important role in determining retinal image quality. While pupil responses to near-visual stimuli have been studied in adults, little is known about their characteristics during visual development. This study investigates three aspects of pupil responses in typically developing infants & children that contribute to retinal image quality during habitual near tasks: i) responses to gradual changes in near-visual demands, ii) consensuality in the two eyes & iii) stability of steady-state responses.
In experiments i & ii, <1yr old infants (n=20), 2-4yr old children (n=20) & adults (n=20) watched a high contrast cartoon movie on an LCD screen (4cd/m2 with dark surround) that ramped between 80 & 33cm, with a stable period of 4s at each viewing distance, either binocularly or monocularly (right eye occluded with an IR transmitting filter). In experiment iii, 8 <1yr olds & 8 adults watched the movie binocularly for 1min at a constant 80cm viewing distance. Pupil diameter was recorded (25Hz) in all conditions using the PowerRefractor.
Pupil diameter reduced for all ages when the target moved from 80 to 33cm. This change with viewing distance (Δpd) was similar in both eyes of infants, children & adults [binocular: p=0.97; monocular: p=0.61] & transient in a number of subjects across all age groups. There was a modest qualitative trend towards Δpd being lowest in youngest infants. 2-factor ANOVA on Δpd showed significant main effects of age (Mean±1STD Infants=0.33±0.04mm; Children=0.21±0.04mm; Adults=0.54±0.04mm) & viewing condition (Binocular=0.44±0.03mm; Monocular=0.27±0.04mm) [p=0.001]. Interaction was not significant [p=0.51]. Post-hoc tests of age (with no assumption of equal variance) showed the mean Δpd of infants & children to be significantly different from that of adults [both p<0.001] but not from that of each other [p=0.34]. The inter-subject variability of Δpd also increased significantly with age [p<0.001]. RMS deviations of steady-state pupil diameter were similar in infants (0.12±0.05mm) & adults (0.16±0.06mm) [p=0.25].
Pupil responses of typically developing infants & children to near-visual stimuli are consensual in the two eyes, with steady-state fluctuations similar to those of adults. Smaller Δpd in infants & children indicate that the developing pupil system may contribute less towards optimizing retinal image quality for slow moving objects than for adults. Larger Δpd in binocular than monocular conditions reflects the importance of binocular cues in driving near-pupil responses during visual development.
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