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Vidhyapriya Sreenivasan, Erin Babinsky, Yifei Wu, T Rowan Candy; Accommodation and vergence during measurement of fusional ranges in infants and pre-school children. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3995.
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© ARVO (1962-2015); The Authors (2016-present)
Accurate binocular alignment requires motor fusion, which must compensate for heterophoria. Infants and young children experience uncorrected hyperopia and narrow IPDs that could lead to excessive convergence (and esophoria) resulting from neural coupling. How well are fusional reserves coping with this challenge? This study evaluated accommodation and vergence behaviour of infants and young children during measurement of vergence ranges to determine fusional reserves around their phoria.
Purkinje image tracking and eccentric photorefraction (MCS PowerRefractor) were used to record eye alignment and accommodation in infants (Inf) (3 to 5 months; n=17), pre-school children (PreSch) (2.5 to 5 years; n=19) and uninstructed, naïve pre-presbyopic adults (Ad) (n=14). Phoria was derived from the difference between eye alignments measured in monocular and binocular viewing, while viewing a naturalistic target at 80 cm. Motor fusion was measured objectively with the photorefractor by introducing base-in (BI) and base-out (BO) prism (2-40pd). The prism value at which motor fusion failed was computed .
Mean OD spherical equivalent refraction was +2.4D (SD ±1.2) in infants and +1.1D (± 0.6) in pre-schoolers. The average phoria was not significantly different (p=0.11) with age (Inf:-0.79 ±2.5 pd; PreSch:-2.43±2.0 pd; Ad:-1.0±2.7 pd). Mean vergence range was also similar between groups for BI (Inf = 11.2±2.5; PreSch: 8.8±2.8 pd; Ad: 11.8±5.2) and BO prism (Inf, 13.7±0.4pd; PreSch:15.1±8.3 pd; Ad: 20±9.2pd). Change in accommodation with the highest fusable prism was positive (more accommodation than naturalistic viewing) with BO (Inf:1.69 ±1.4D; PreSch:1.35±1.6D; Ad:1.22±1.0D) and negative for BI (Inf:-0.96 ±0.3D; PreSch:-0.78±0.6D; Ad:-0.62±0.3D), with similar magnitude across age (BO: p=0.6; BI: p=0.4).
Despite typical levels of hyperopia, infants and young children exhibited small exophorias, that were comparable in mean to adults. Furthermore, participants in all age groups demonstrated substantial fusional reserves, evidence that the youngest participants are capable of responding to a large range of disparities. Accommodation increased wih BO and relaxed with BI by similar amounts across age. Collectively, these data suggest that motor performance is compensating for developmental hyperopia and IPD, in that these characteristics remain consistent with age.
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