Abstract
Purpose :
Vergence insufficiency, impaired saccades contribute to depth perception deficits, poor navigation, and increased fall risk in PD patients. 1/3rd of PD patients also have strabismus and disabling double vision. DBS is becoming increasingly common for improving general motor symptoms of PD. In this study we examined the effects of bilateral STN DBS on the binocular coordination of saccades in PD.
Methods :
We measured binocular eye positions during gaze-holding and saccades using high-resolution video-oculography (Eyelink1000™) in twenty PD patients and seven healthy controls. Saccades were quantified by placing LED targets at 150 cm distance on an isovergence circle with angle of ±10° and ±20°. Subsequently, clustering was performed to analyze gaze-holding performance. Saccades were identified and analyzed using the Engbert algorithm.
Results :
Binocular coordination in PD was significantly better with DBS switched ON, as compared to OFF (p<0.05). Supervised clustering was applied to gaze fixation data in order to assess performance. Controls had a mean of maximal deviation (Horizontal: 1.9±0.56°, Vertical: 1.94±0.6°) significantly different from PD DBS OFF (Horizontal: 3.08±2.98°, Vertical: 1.54± 1.40°), but not from PD DBS ON (Horizontal: 1.71± 1.28°, Vertical: 1.27± 1.4°). This was also reflected in saccade tasks with fusion maintenance. Post saccade drift variance in controls (Mean:0.01±0.03°; p<0.05) was found to be different from PD with DBS OFF (Mean:0.19±0.76°). Meanwhile, there was no difference in post saccade drift variance between controls and PD DBS ON (Mean:0.01±0.02°). The difference in latency of controls (Mean:0.244±0.029msec), PD DBS ON (Mean:0.50±0.47msec) and PD DBS OFF (Mean:0.32±0.11msec) approaches statistical significance (p=0.09).
Conclusions :
Objective analysis of gaze-holding and saccadic eye movements suggest that saccadic abnormalities and strabismus are prevalent, significant, and interrelated in PD. The results suggest that STN-DBS affects the neural pathway common to both vergence and saccades, possibly by acting on the STN–substantia nigra pars reticulata–superior colliculi pathway. These findings provide novel insights into the pathophysiology of Parkinson's disease and may yield better treatment strategies for strabismus, including using STN DBS.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.