Uncorrected low hyperopia in young subjects induces postural instability even in those with clear visual acuity
by Byeong-Yeon Moon, Hyun Gug Cho, Dong-Sik Yu, Sang-Yeob Kim
Reports have indicated the effect of myopic blur on postural stability. The objective of this study was to investigate the minimum refractive error to significantly affect postural stability through a various levels of hyperopia and myopia induced by ophthalmic lenses. Forty subjects with a mean age of 22.95 ± 2.21 years were enrolled. In all subjects, the subjective refraction with MPMVA (Maximum to Plus Maximum Visual Acuity) was performed to correct refractive error. To induce hyperopia and myopia, spherical lenses of ±1.0, ±2.0, ±3.0, ±4.0, ±5.0 and ±6.0 D were used on top of the trial frame with corrected condition as MPMVA (eyes-open with MPMVA). Under each induced-refractive error condition, general stability (ST) and sway power (SP) in frequencies by each subsystem were measured with Tetrax posturography with firm plates at patient’s upright position, after performed the measurements under the conditions of eyes-open with MPMVA and eyes-closed. ST at eyes-closed was significantly greater than that at eyes-open with MPMVA (p < 0.001). ST was increased significantly for induced hyperopia of -1.0 D (p < 0.001) with decimal visual acuity of 1.07 ± 0.17 and for induced myopia of +3.0 D (p = 0.011) with decimal visual acuity of 0.16 ± 0.09, as compared to that at eyes-open with MPMVA. No significant difference was observed between induced hyperopia of -6.0 D and those at eyes-closed only. SP was increased significantly at low medium-frequencies of the peripheral vestibular signals in induced hyperopia, moreover, hyperopia induced at -6.0 D lenses was significantly different compared to that at eyes-open with MPMVA. Uncorrected low hyperopia in young subjects may lead to postural instability, although they can obtain clear vision. The corrected state of ametropia, especially hyperopia, is a more important factor of appropriate visual input in stable postural adjustment than visual acuity.