Abstract
Purpose :
Small vessel ischemia (SVI), also commonly called “white matter disease” is a common phenomenon in elderly individuals. Often, these small strokes in the cerebral white matter can manifest symptoms that mimic Parkinson’s disease, and are often referred to a Movement Disorder clinic for diagnosis. Some small strokes are expected with advanced age, and may add to difficulty in differentiating idiopathic Parkinson’s Disease from small vessel ischemia. This study examines the effects of small vessel strokes during horizontal tracking as an objective measure to assist in clinical diagnosis of SVI.
Methods :
In an ongoing study, the eye movements of 100 veterans diagnosed with MRI-confirmed SVI and 100 controls were recorded binocularly at 500 Hz (SR Research, EyeLink II). Participants were instructed to track spatially and temporally randomized step changes in target position along the horizontal axis. Data were analyzed for response latency, saccadic amplitude, duration, velocity and acceleration, including position accuracy and fixation stability. Statistical analysis was performed on all eye measurement parameters using ANOVA.
Results :
While the eye movements for controls were within normal ranges, specific abnormalities were found in subjects with SVI. Most notably, main sequence analysis showed almost twice as much variability in saccadic peak velocity for a given amplitude compared to controls. While saccadic peak velocity for controls exhibited a spread of ~75°/s at 20° amplitude, SVI subjects had an increased spread of almost 130°/s. Additionally, the saccadic waveform tends to be distorted in SVI, with 85% of subjects exhibiting small peaked dynamic overshoots (typically <5% of total saccadic amplitude), along with post-saccadic ringing that dampened into stable fixations. The latency of saccades between controls and SVIs were not significant. Fixation RMS velocity among controls was slightly less, implying more stable fixation compared to SVIs.
Conclusions :
SVI produces significant alteration of consistency within saccadic main sequence, as well as altering saccadic termination behavior. Fixation stability may also be an important indicator of SVI status. The present combined findings suggest that eye movement parameters could be a sensitive clinical means to differentiate SVI and, as such, provide a valuable tool to clinicians.
This is a 2020 ARVO Annual Meeting abstract.