Objective: This study aimed to evaluate the visual evoked potentials (VEP) and optical coherence tomography (OCT) as a diagnostic biomarker in Parkinson's disease (PD) patients. Patients and Methods: Forty-seven PD patients were distributed to two groups: Group 1-included 22 newly diagnosed drug naïve PD patients. Group 2-included 25 PD patients receiving antiparkinsonian drugs. Another 20 age and sex-matched healthy subjects were recruited and served as a control group (Group 3). All participants were subjected to full medical history, general and neurological examination. All participants underwent a full neuro-ophthalmologic examination, OCT, and VEP. Results: The VEP assessment revealed that the p100 latency was significantly delayed in patients' groups in comparison to healthy subjects (p < 0.0001). Also, the p100 amplitude was significantly diminished in patients' groups in comparison to healthy subjects (p < 0.0001). These parameters showed statistically significant correlations with both disease duration and severity. There was a significant reduction in both average and quadrant Retinal Nerve Fiber Layer (RNFL) thickness (p < 0.0001) in PD patients compared to healthy subjects, with more affection of group 2. Decreased average RNFL thickness was correlated to PD duration and severity. In PD patients both delayed P100 Latency and decreased amplitude were in a statistically significant correlation with decreased average RNFL thickness. Conclusion: Our results indicate PD patients either drug naïve or medicated show functional and morphological changes in the visual pathway, these changes represent a new biomarker for follow up of PD progression.