Vertical optokinetic nystagmus in adults with or without Parkinson's Disease

Background: Horizontal OKN is widely investigated and it is accepted that there is no horizontal OKN asymmetry in healthy adults. Vertical OKN is less well investigated and the direction of vertical OKN asymmetry is unclear. Aims: To investigate vertical OKN asymmetry in healthy individuals under of variety of different experimental conditions comparing: (i) the performance of look versus stare OKN, the effects of (ii) stimulus velocity, (iii) luminance profile, (iv) stimulus size and shape, and (v) distance on vertical OKN responses. The effect of neurological disease on OKN asymmetry in the form of Parkinson's disease was also investigated. Methods: OKN responses were recorded in healthy adult volunteers under a variety of experimental conditions including: (i) working distances of 33cm, lm, 1.2m and 2.5m (ii) sinusoidal and square wave OKN targets (iii) different target sizes ranging in size from 22.4°x28.9° to 65°x 55° (iv) contrasts of 50% to 100% and (v) target velocities of 20°/s and 40°/s investigating 'look and 'stare' OKN response. Stare OKN responses were also compared in subjects with Parkinson's disease and age-matched controls. All data was recorded using an infrared video pupil tracker. Result: No clear vertical OKN asymmetry was seen in normal adult subjects although the degree and direction of vertical OKN asymmetry remained relatively consistent for an individual under different stimulus conditions. Of all stimulus parameters target size had the greatest effect on vertical OKN asymmetry. Stare OKN was sensitive to distance for stimuli moving in the downwards direction. Parkinson's disease patients also had greatly reduced OKN responses for stimuli moving in the downward direction. Discussion: We found sensitivity of 'stare' OKN responses during downward stimulation to both target distance and the effects of Parkinson's disease. It is possible that this is related to the function of OKN during navigation, which is under cerebellar control.EThOS - Electronic Theses Online ServiceGBUnited Kingdo