Abstract
The majority of individuals with Down syndrome (DS) do not exhibit accurate accommodation, with the aetiology of this deficit unknown. This study examines the mechanism underlying hypoaccommodation in DS by simultaneously investigating the ‘near triad’ – accommodation, vergence and pupillary response. An objective photorefraction system measured accommodation, pupil size and gaze position (vergence) under binocular conditions while participants viewed an animated movie at 50, 33, 25 and 20 cm. Participants were aged 6–16 years (DS = 41, controls = 76). Measures were obtained from 59% of participants with DS and 99% of controls. Accommodative response was significantly less in DS (p < 0.001) and greater accommodative deficits were associated with worsening visual acuity (p = 0.02). Vergence responses were as accurate in DS as in controls (p = 0.90). Habitual pupil diameter did not differ between groups (p = 0.24) but reduced significantly with increasing accommodative demand in both participants with and without DS (p < 0.0001). This study is the first to report simultaneous binocular measurement of the near triad in DS demonstrating that hypoaccommodation is linked to poor visual acuity. Vergence responses were accurate indicating that hypoaccommodation cannot be dismissed as a failure to visually engage with near targets, but rather is a consequence of underlying neurological or physiological deficits.
Highlights
The majority of individuals with Down syndrome (DS) do not exhibit accurate accommodation, with the aetiology of this deficit unknown
The study protocol was approved by the University of Ulster Research Ethics committee, the Office for Research Ethics Committees Northern Ireland (ORECNI) and the Research Office of the Western Health and Social Care Trust (WHSCT)
There was no significant difference in age, SER or best corrected visual acuity (BCVA) between participants with DS whose data were available for analysis and those whose data were not (p > 0.05)
Summary
The majority of individuals with Down syndrome (DS) do not exhibit accurate accommodation, with the aetiology of this deficit unknown. This study examines the mechanism underlying hypoaccommodation in DS by simultaneously investigating the ‘near triad’ – accommodation, vergence and pupillary response. Vergence responses were accurate indicating that hypoaccommodation cannot be dismissed as a failure to visually engage with near targets, but rather is a consequence of underlying neurological or physiological deficits. When a near object is viewed, a simultaneously focused and single retinal image is achieved by the activation and neural control of the accommodative and vergence response systems[11]. The majority of studies investigating accommodative function in DS have explored accommodation and near visual impairment through examining the accuracy of individual participant’s focus on near targets, without consideration of the other components of the triad (vergence and pupil size). The aim of the present study is to simultaneously assess accommodation, vergence and pupil response during a near vision task in children with DS and compare the findings to those from typically developing children
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