Biomedical Sciences Research Institute, University of Ulster, Cromore Road, Coleraine, Northern Ireland, BT52 1SA.
Sci Rep. 2017 Jan 10;7:39860. doi: 10.1038/srep39860.
Individuals with Down syndrome (DS) often exhibit hypoaccommodation alongside accurate vergence. This study investigates the sensitivity of the two systems to retinal disparity and blur cues, establishing the relationship between the two in terms of accommodative-convergence to accommodation (AC/A) and convergence-accommodation to convergence (CA/C) ratios. An objective photorefraction system measured accommodation and vergence under binocular conditions and when retinal disparity and blur cues were removed. Participants were aged 6-16 years (DS n = 41, controls n = 76). Measures were obtained from 65.9% of participants with DS and 100% of controls. Accommodative and vergence responses were reduced with the removal of one or both cues in controls (p < 0.007). For participants with DS, removal of blur was less detrimental to accommodative responses than removal of disparity; accommodative responses being significantly better when all cues were available or when blur was removed in comparison to when proximity was the only available cue. AC/A ratios were larger and CA/C ratios smaller in participants with DS (p < 0.00001). This study demonstrates that retinal disparity is the main driver to both systems in DS and illustrates the diminished influence of retinal blur. High AC/A and low CA/C ratios in combination with disparity-driven responses suggest prioritisation of vergence over accurate accommodation.
唐氏综合征（DS）患者通常表现出调节不足，同时伴有准确的聚散。本研究通过测量调节性集合与调节（AC/A）和聚散性集合与聚散（CA/C）比值，调查两个系统对视网膜离差和模糊线索的敏感性，确定这两个系统之间的关系。双眼条件下，当去除视网膜离差和模糊线索时，客观眼折射系统测量调节和聚散。参与者年龄为 6-16 岁（DS 组 n=41，对照组 n=76）。DS 组中 65.9%的参与者和 100%的对照组获得了测量值。在对照组中，去除一个或两个线索都会降低调节和聚散的反应（p<0.007）。对于 DS 患者，与去除离差相比，去除模糊对调节反应的影响较小；当所有线索都可用或仅去除模糊时，调节反应明显更好。DS 患者的 AC/A 比值较大，CA/C 比值较小（p<0.00001）。本研究表明，在 DS 中，视网膜离差是两个系统的主要驱动因素，并说明了视网膜模糊的影响降低。高 AC/A 和低 CA/C 比值与离差驱动的反应相结合，表明优先考虑聚散而不是准确的调节。
