Assessment of subjective visual vertical, fall risk, and objective and subjective vestibulo-ocular reflex in obstructive sleep apnea syndrome

Obstructive Sleep Apnea Syndrome (OSAS) is a disorder characterized by recurrent episodes of apnoea (cessation of breathing) and hypopnoea (marked reduction in airflow) due to repetitive narrowing or complete collapse of the upper airway during sleep. This doctoral study aimed to provide a multidimensional evaluation of the vestibular system in individuals with OSAS. To this end, in addition to assessing the vestibulo-ocular reflex (VOR) objectively and functionally/subjectively, perceptual visual measures and fall risk were examined, and comparative analyses were conducted for fall risk. The video Head Impulse Test (vHIT), functional Head Impulse Test (fHIT), the Tinetti Balance and Gait Test, and subjective visual perception tests—static and dynamic subjective visual vertical (SVV) and horizontal (SVH)—were administered. In this cross-sectional design, a total of 67 participants were included: 22 with moderate OSAS, 22 with severe OSAS, and 23 healthy controls aged 18–55 years. Participants in the OSAS groups were diagnosed via polysomnography. To ensure the absence of sleep problems in the control group, the Pittsburgh Sleep Quality Index was applied and those with a total score ≤5 were included. All participants underwent otorhinolaryngologic examination, and cognitive eligibility was verified with the Mini-Mental State Examination (MMSE >24). The findings showed that body mass index was higher in both OSAS groups than in controls (p<.05; significant for control–moderate and control–severe, non-significant between moderate and severe). Fall risk was increased in both OSAS groups compared with controls (p<.05). A group effect was observed in visual perception tests except for SVH (p>.05); pairwise differences were most pronounced between severe OSAS and controls in dynamic SVV and dynamic SVH, whereas significance did not persist for SVV after Bonferroni-corrected comparisons. No between-group differences were found in vHIT gains (p>.05). In contrast, fHIT revealed reductions in correct-response percentages, with the most prominent difference between severe OSAS and controls (p<.05). Correlation analyses indicated no association between Tinetti scores and subjective visual perception tests; Tinetti correlated moderately and positively with vHIT only for the left posterior semicircular canal in the severe OSAS group, and showed moderate-to-strong positive correlations with fHIT in both moderate and severe OSAS. In conclusion, fall risk is elevated in obstructive sleep apnea (OSA), and even when vHIT remains within normal limits, fHIT can detect functional VOR deficits; therefore, comprehensive vestibular assessment in OSA should include both functional and subjective/perceptual measures. Keywords: OSAS, vHIT, fHIT, subjective visual tests, fall risk