Objective: To evaluate the relationship between Contrast Sensitivity (CS) and cognitive function in patients with idiopathic Parkinson’s Disease (PD) and healthy controls (HC).

Background: In addition to the motor aspects of PD, the associated cognitive impairment and visual dysfunction negatively impact life quality and safety in patients with PD [1]. One described etiology for the visual impairment is the thinning of dopaminergic layers in the retina, resulting in impaired CS [2].

Method: We evaluated 40 PD participants and 43 matched HC, 46-82 years old, with bilateral visual acuity of at least 20/50. We measured CS with the Pelli-Robson chart (from one meter). We calculated an Executive Function Domain Score by averaging the z-scores from tests of executive function (Trails Making Test B-A, Delis-Kaplan Executive Function System Stroop color-word interference test Inhibition and Inhibition/Switching) and a Processing Speed Domain Score from tests of processing speed (Trails A, Stroop Color Naming and Stroop Word Naming). We also administered the Psychomotor Vigilance Task (PVT) to both groups and recorded the duration of disease (DOD) and levodopa equivalent dose (LED) in the PD group. We stratified both PD and HC groups into normal CS (CSN) vs. impaired CS (CSI) based on the age-adjusted normative values provided by Mäntyjärvi et al.: 1.82 cut-off value for CSN in the age group 40-59 years, and 1.71 in the age group 60+ [3].

Results: PD participants had worse CS and performed worse than the HC on all cognitive tests. The PD CSI group had longer DOD and a trend toward higher LED than the PD CSN group. The PD CSI group also had slower reaction time and more lapses on the PVT. The Processing Speed Domain Score correlated with the CS values in both PD and HC, and the Executive Function Domain Score showed a tendency to significance in the PD group.

Conclusion: Compared to HC, PD patients have worse CS, particularly those with more advanced disease and those requiring more dopaminergic therapy. CS impairment is associated with worse performance on cognitive testing. Thus, evaluating PD patients for CS may allow more individualized patient care and earlier treatment with improved outcomes. Further research is needed to fully understand the causes of visual impairment in PD and its temporal relationship with cognitive function.
Part of this work was previously presented at the American Academy of Neurology (AAN) 2016 Annual Meeting.

References: [1] Leyland LA, Bremner FD, Mahmood R, et al. Visual tests predict dementia risk in Parkinson disease. Neurol Clin Pract. 2020;10(1):29-39. doi:10.1212/CPJ.0000000000000719. [2] Weil RS, Schrag AE, Warren JD, Crutch SJ, Lees AJ, Morris HR. Visual dysfunction in Parkinson’s disease. Brain. 2016;139(11):2827-2843. doi:10.1093/brain/aww175. [3] Mäntyjärvi M, Laitinen T. Normal values for the Pelli-Robson contrast sensitivity test. J Cataract Refract Surg. 2001;27(2):261-266. doi:10.1016/s0886-3350(00)00562-9.

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