Ph.D. Dissertation Defense
Candidate: Palak Gupta
Thesis Advisor: Aasef G. Shaikh, MD PhD.
ABSTRACT
Parkinson’s disease is a progressive neurodegenerative disorder affecting adults with motor symptoms as hallmark symptoms. Recent research has however shown it to be a multifaceted disorder with a myriad non-motor symptoms. Eye movement deficits are an under-recognized and less understood symptom in Parkinson's Disease (PD), affecting at least half of the PD population in some form. Differentiating PD-related ocular motor deficits from age-related or congenital abnormalities presents significant challenges. Recent research has established a relationship between PD and ocular motor dysfunction (OMD), revealing that the pathological firing from the basal ganglia circuitry, where PD originates, disrupts the pathways controlling ocular motor behavior.
This study delineates three primary ocular motor deficits in PD: vergence, saccades, and fixational stability or strabismus. Our findings indicate that PD affects these behaviors in distinct ways. Vergence is impaired by decreased gains, altered trajectories, and decreased fusion maintenance, leading to difficulties in maintaining binocular vision. Saccadic movements show decreased conjugacy, increased latencies, and slower trajectories, resulting in less accurate and coordinated eye movements. Fixational instability is observed as increased exodeviation and an increased angle of strabismus, which further compromise visual stability.
Additionally, our research explores the impact of therapeutic interventions on ocular motor behavior in PD. Deep brain stimulation (DBS), commonly used to manage motor symptoms such as tremor and rigidity in PD, also alters ocular motor function. Unlike levodopa, which produces no effect on OMD, DBS was shown to influence fibers in the ocular motor network. In 75% of cases with recognized PD-related ocular motor deficits,DBS improved vision-related quality of life to varying extents. However, the benefits of DBS on ocular motor responses depend on the specific location and region of stimulation, with some configurations potentially exacerbating the deficits.
This study underscores the importance of recognizing and addressing ocular motor deficits in PD. It highlights the need for further research to refine therapeutic strategies like DBS, ensuring that they not only alleviate motor symptoms but also enhance ocular motor function and overall visual quality of life for individuals with PD. The intricate relationship between the basal ganglia circuitry and ocular motor control necessitates a multidisciplinary approach to develop comprehensive treatment protocols for PD patients. Future studies will help address these nuances and help inform personalized treatments and improve outcomes.