Background: Parkinson's disease is a neurodegenerative disease. Cognitive disorders and retinal degeneration may occur during the early stages of the disease. Retinal degeneration and cognitive findings can be assessed easily with optical coherence tomography and mini-mental test, respectively. Materials and Methods: Twenty-two patients who are being followed-up with Parkinson's disease and 22 healthy controls have been included in the study. The Unified Parkinson's Disease Rating Scale (UPDRS) and Hoehn-Yahr staging of the patients have been conducted at the time of admission. Retinal nerve fiber layer analysis and ganglion cell thickness (ganglion cell complexes [GCCs]) were evaluated through optical coherence tomography (OCT). And at the same time, we aimed to compare the stage of the disease, the UPDRS score and the duration of the disease with OCT and cognitive functions by mini-mental test. Results: Mini-mental test total score value (P = 0.025) and language value (P = 0.021) were lower in the patient group compared to the control group. In patients, there is a reverse significant correlation between UPDRS-T and GCC-left-superior (r = -0.495; P = 0.026), GCC-left-inferior (r = -0.517; P = 0.019), and GCC-left-to (r = -0.508; P = 0.022). There is a significant parallel relation between recall and RFNL-right-mean (r = 0.626; P = 0.039). Conclusion: Our findings indicate that the neurodegeneration continues multisystemically and neurodegeneration increases simultaneously with the disease. OCT, which is a noninvasive method, can be used as an indicator of neurodegeneration in patients with P arkinson's disease.