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Lesley Doyle, Julie-Anne Little, Kathryn J Saunders; Vergence and Accommodation in Down Syndrome: exploring the role of disparity and blur cues. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3762. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Previous research has demonstrated that the prevalence of hypoaccommodation in children with Down syndrome (DS) ranges from 55-100% (Woodhouse et al 1993; Haugen et al 2001; Stewart et al 2007; Nandakumar & Leat 2009). The aetiology of this deficit is unclear; various sensory and mechanical deficits have been proposed. The accommodative system is stimulated by retinal disparity, blur and proximity cues. The purpose of this investigation is to assess the relative contribution of individual cues in driving the accommodative response (AR) and the relation between accommodation and vergence in children with DS.
Participants were 24 children with DS (1 emmetrope, 4 myopes, 19 hyperopes) and refractive error matched controls aged 6-16 years. Appropriate refractive correction was worn following full optometric workup. Participants were classified using dynamic retinoscopy (DR) as having either accurate or inaccurate accommodative response to a target demand of 4D. AR and vergence were assessed using an infrared photorefraction system (PowerRefractor III) at demands of 1, 2, 3, 4 and 5D under 4 cue conditions; (i) all cues available; removal of (ii) disparity, (iii) blur cue (iv) blur and disparity cues. Accommodative demand/response slopes were calculated for each condition and AC/A and CA/C ratios derived from (ii) and (iii).
Useable data were obtained for one or more conditions in 71% (n=17) of participants with DS and 100% of controls. Of these, 6 were classified as having inaccurate DR response and 11 were accurate. All controls had accurate DR responses. There was a significant difference in AR slopes between cue conditions (F(3,115)=9.82, p<0.00001) and the DS slope values were significantly less under conditions (i), (ii) and (iii). The AC/A ratio in the DS group was larger than controls (t(26)=2.41, p=0.01) and the CA/C ratio smaller (t(25)=2.01, p=0.03). AC/A ratios remained significantly larger than controls when considering DS participants with and without accurate DR responses (accurate t(18)=2.23, p=0.02; inaccurate, t(9)=2.27, p=0.02). However, DS participants with inaccurate DR responses demonstrated higher AC/A ratios than those with accurate responses (t(13)=-1.73, p=0.05).
These data further characterise the accommodative deficit in children with DS implying an abnormal relationship between accommodation and vergence which requires further study.
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