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Zhanhan Tu, Christopher Degg, Viral Sheth, Rebecca McLean, Peter O'Hara, Irene Gottlob, Frank A Proudlock, Ophthalmology Group; Postural stability in infantile nystagmus. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5103.
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© ARVO (1962-2015); The Authors (2016-present)
In normal humans, somatosensory (SOM) inputs are the primary inputs for maintaining postural stability, followed by vision, then vestibular inputs. Deficits in balance have been described in idiopathic infantile nystagmus (IIN) using Computerized Dynamic Posturography (CDP), concluding that greater relative emphasis is placed on SOM and vestibular inputs in IIN, and less on vision. CDP has not been applied to albinism in which both nystagmus and visual afferent deficits occur. We investigated the role of vision on postural stability in albinism and the weighting placed on sensory inputs in albinism.
10 participants with albinism, 7 with IIN and 14 controls underwent the sensory organization test (SOT) using CDP which has a sway-referenced (SR) platform to negate SOM inputs and also a SR visual surround. The Equilibrium Score (ES) was used to estimate the relative importance of the three inputs using the scoring system shown in table 1.
In contrast to previous findings, overall balance performance for the 6 conditions was almost identical and performance was relatively good in all 3 groups in the 3 conditions with a fixed platform. The largest differences were observed when negating SOM inputs using the SR platform mode where deprivation of vision (by closing the eyes, C5/C4) led to much greater drop in balance performance in the control group than in the albinism (p=0.002) and IIN (p=0.009) groups. However, albinism performed better than controls when only vestibular inputs were available (p=0.031).
Overall balance performance was better than expected in albinism and IIN since these two groups relied less on vision than controls and could cope with deprivation of vision better, especially in conditions where proprioception is compromised. Individuals with IIN and albinism do not appeared to use proprioceptive inputs differently to controls as evidenced by their good performance overall with a fixed platform. Individuals with IIN appear to use proprioceptive, visual and vestibular cues in a similar way to the controls. However, individuals with albinism use vision and vestibular cues with similar weighting.
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