Retinal nerve fiber layer thickness and its correlation with Parkinson’s disease severity

Background and objectives. Parkinson's disease (PD) is a neurodegenerative disorder characterized by a reduction in dopamine levels in the brain. Dopamine is also found in the ganglion cell layer of the retinal nerve fiber layer (RNFL), suggesting that the total retinal thickness may be impacted by dopamine decline in PD. The Parkinson's Disease Composite Scale (PDCS) is a reliable and efficient tool for measuring PD severity. This study aimed to investigate the correlation between PD severity and RNFL thickness. Materials and methods. A cross-sectional study was conducted with 25 PD patients. PDCS-based severity assessment was recorded, including aspects related to disability, non-motor and motor symptoms, and drug complications. RNFL thickness was measured using optical coherence tomography (OCT), with results divided into the following quadrants: temporal-superior, nasal-superior, temporal, nasal, temporal-inferior, nasal-inferior, and global. Results. A significant negative correlation was found between PD severity and RNFL thickness in the nasal-superior quadrant (p = 0.0224; r = -0.4547). Significant negative correlations were also observed between the nasal-superior quadrant and the motor (p = 0.0326; r = -0.4285), non-motor (p = 0.0081; r = -0.5172), and disability aspects (p = 0.0293; r = -0.4361). Conclusions. PD severity is associated with RNFL thinning, particularly in the nasal-superior quadrant. Limitations of this study include the small sample size and the absence of a control group, which may affect the generalizability of the findings. These results highlight the potential of RNFL thickness as a biomarker for PD progression, and future studies should explore the role of retinal changes in PD monitoring and treatment strategies.