Trying to see, failing to focus: near visual impairment in Down syndrome

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.

Determining the relative contribution of retinal disparity and blur cues to ocular accommodation in Down syndrome

“…Recruitment of 76 typically developing control participants and 41 participants with DS aged 6–16 years was carried out as described in a recently published study12. The study received ethical approval from the University of Ulster Research Ethics committee and the Office for Research Ethics Committees Northern Ireland, and research governance was obtained through the University of Ulster and the Research Office of the Western Health and Social Care Trust.…”

“…Refractive power and eye position calibration was attempted on all participants using spherical full aperture trial lenses and prisms of known power (+4, +3, +2, +1, −2, −4D spherical lenses and 4, 8, 12 and 16 Δ base in and base out prisms)1213. Lenses/prisms were placed in front of the non-dominant eye in combination with an infrared (IR) transmitting filter (Edmund Optics, USA) to occlude visible light.…”

“…The authors have previously reported simultaneous measurement of accommodation, vergence and the near pupillary response using photorefraction under naturalistic conditions, demonstrating that underaccommodation accompanies accurate vergence in the majority of participants with DS12. The aim of the present study is to determine the relative contribution of both the retinal disparity and retinal blur cues in driving the accommodative and vergence systems in DS and to assess the relationship between the two systems in terms of AC/A and CA/C ratio.…”

Disorders in melanopsin effect of pupil constriction as a risk factor causing eye diseases

“…Pupil constriction and retention mechanism at accommodation and convergence is interesting for researchers when they solve applied tasks [25,27]. Researchers in their experiments applied LCD-displays, OLEDmicrodisplays, and a white sheet of paper with letters lit by an incandescent lamp, to create visual images.…”

“…Other researchers use LCD-display for watching movies as a visual stimulus, and their volunteers were children (a very relevant focus group nowadays) aged from 6 to 16 [27]: 76 were regularly developed children and 41 children had Down's syndrome (DS). Research allowed to obtain dependence of changes in pupil diameter on accommodation level ( Figure 9).…”