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Vidhyapriya Sreenivasan, Elise Ciner, Whitley Harbison, Brian Alva, Marjean T Kulp, T. Rowan Candy; Objective near heterophoria in emmetropic and hyperopic preschool children. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2745.
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The accommodation and vergence ocular-motor systems must provide adequate retinal image quality and alignment to permit typical postnatal development. Uncorrected hyperopia and narrow intraocular separation represent apparently conflicting stimuli to these motor systems, resulting from the neural coupling between their responses. Increased uncorrected hyperopia could lead to increased accommodative convergence and an esophoria or esotropia, if a child is generating accurate accommodation responses. This study evaluates whether phoria in preschoolers is related to refractive error, and how accommodative responses might impact typical cover test assessments.
Eccentric photorefraction and Purkinje image eye tracking (MCS PowerRefractor) were used to record accommodation and eye alignment simultaneously. Responses were obtained from 31 emmetropic or hyperopic children ages 4 to 6 years without strabismus or amblyopia and no previous habitual spectacle correction. Children viewed an animated cartoon at 33cm monocularly for 60 sec followed by a binocular viewing period of 2 minutes. Dissociated heterophoria and accommodative measures were derived from the difference between the responses in the 2 conditions.
Objective estimates of near phoria were obtained from 23 children (Sph.Eq.: -0.5 D to +4 D, mean= +1 D). 95% CI were calculated for each estimate of mean vergence, to indicate the stability of vergence responses. Mean phoria at 33 cm was 3.9 pd exophoria (SD: 4.3 pd). The relationship between phoria and Sph.Eq. was minimal (r2=0.03), while phoria and accommodation change between monocular and binocular viewing were more related (r2=0.25) for this naturalistic target.
These data suggest that at least some preschool non-strabismic hyperopes, can achieve typical small exophoria at near, as measured by Purkinje image eye tracking, with somewhat variable changes in accommodation. These data suggest that a broader range of hyperopes should also be examined.
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