Effect of induced astigmatism on vestibulo-ocular reflex

Clinical relevanceThe vestibular-ocular reflex stabilises the retinal image and maintains balance during head movement. Astigmatism is one of the common refractive errors that can reduce the quality of visual inputs.BackgroundThe purpose of this study was to investigate the effect of induced astigmatism on the function of the vestibular-ocular reflex.MethodsThis prospective semi-experimental study was conducted on 48 participants aged 20 to 40 years who had no history of neurological, vestibular, or eye disorders. Simple myopic astigmatism was induced using three positive cylindrical lens powers of + 0.50D, +1.50D, and + 2.50D at three axes of 180, 45, and 90 degrees in both eyes. The vestibular-ocular reflex was evaluated by the ocular Vestibular Evoked Myogenic Potential (oVEMP) through acoustic stimulation (a 500 hz tone burst at an intensity of 95 dBnHL) of the ear, with potentials recorded from the lower oblique muscle. The latency of the N1 and P1 waves and the amplitude of N1-P1 were recorded for all participants in the baseline condition (without any induced astigmatism) and under different induced astigmatism conditions.ResultsThe latencies of N1 and P1 significantly increased with the increasing power of induced astigmatism; however, the powers of astigmatism had no effect on the amplitude of N1-P1. The axes of induced astigmatism did not have a significant effect on the latencies and amplitude of N1-P1.ConclusionsInduced astigmatism due to retinal image blur can deteriorate the function of the vestibular-ocular reflex by increase in the latencies of N1 and P1 oVEMP waves.