To date, there has been no clear evidence regarding the evaluation of saccades as a monitoring tool of motor impairment in Parkinson's disease (PD) Subthalamic Nucleus Deep Brain Stimulation (STN-DBS) patients. The aim of this study was to evaluate the long-term impact of STN-DBS and pharmacological treatment on reflexive saccades' (RS) parameters and UPDRS alterations. The DBS group consisted of 20 PD patients who underwent bilateral STN-DBS. The Postoperative (POP) group consisted of 14 post-DBS patients. The Best Medical Therapy (BMT) group consisted of 20 patients on pharmacotherapy only. RS parameters and the UPDRS scale were measured during three visits in four phases of treatment (i.e. BMT-ON/OFF, DBS-ON/OFF). The significant UPDRS III and UPDRS. Total improvements were observed in all three study groups (p < 0.05), but RS latency improvement was stated only in the DBS group in the DBS-ON phase (p < 0.05). A significant correlation between RS latency increase and UPDRS III score worsening was found in all study groups, with the most evident effect in the UPDRS III ON phase (p < 0.05). RS parameters correlated with UPDRS III outcomes during the postoperative period in DBS-STN patients. Therefore, saccadic evaluation may be a good biomarker of the patient's response to surgical and/or pharmacological treatment.