What Cognition-Based Retinal Nerve Fiber Thickness Tells Us in Parkinson Disease?

Introduction: Non-motor problems, such as cognitive and ophthalmological system findings, are the areas that are affected in idiopathic Parkinson’s disease (IPD) and are stated to be related to the severity of disease. In our study, we aimed to evaluate the relationship between retinal nerve fiber layer (RNFL) thickness and disease stage and cognitive impairment in IPD.Materials and methods: Thirty-four patients diagnosed with IPD and 21 controls were included in the study. The Addenbrooke Cognitive Examination-Revised (ACE-R), and the Digit Span Test were used to evaluate cognitive functions. RNFL thickness was evaluated using optical coherence tomography.Results: The total ACE-R score was significantly lower in the patients compared to the controls (p = 0.007). The mean RNFL value of the right nasal inferior RNFL was thinner in the patient group compared to the control group (p = 0.026). There was a negative and moderate correlation between age, right nasal superior and left temporal inferior RNFL thickness (rho: -0.438 and -0.479, respectively) was observed. There was a positive correlation with right nasal RNFL thickness and verbal fluency in the patients. Right nasal and right nasal inferior RNFL thickness were positively correlated with memory functions.Conclusion: The fact that thinning of the right nasal fibers correlates with cognitive status, the difference in interocular RNFL is more pronounced in patients with a symptomatic right side, and age-related RNFL thinning is associated with right nasal and left temporal fibers suggests that the neurodegenerative process in IPD may be associated with the dominant hemisphere.