Introduction: This study was designed to explore the relationship between retinal nerve fiber layer (RNFL) thickness and cognition in Idiopathic Parkinson's disease (IPD) patients without visual symptoms or diagnosis of dementia. Methods: Groups of patients with idiopathic Parkinson's disease and healthy controls were compared ophthalmologically using optical coherence tomography (OCT) and cognitively through neuropsychological tests. Results: The findings highlighted a pronounced RNFL thinning, especially in the right nasal inferior quadrant of IPD patients compared to the control group. Almost half (47%) of the subjects in the IPD group exhibited issues in one or multiple subcomponents of Addenbrooke's Cognitive Examination-Revised (ACE-R). At the same time, the study suggested that effects in the visuospatial domain may be associated with disease severity in IPD patients. However, the investigation could not establish a direct association between the severity or duration of the disease and OCT measurements. A correlation was observed between certain ACE-R scores and some RNFL quadrants. Conclusion: In conclusion, the inception phases of IPD are characterized by discernable visual pathologies and cognitive anomalies. The thinning of the RNFL, which can be identified through OCT, might serve as a pivotal tool for tracking the early progression of IPD and formulating intervention strategies. That being said, more comprehensive studies are essential to wholly understand OCT's role in the early diagnosis and monitoring of IPD.