The goal of this observational study is to determine whether oxygen content of the retinal vessels of the eye may serve as a biomarker in Parkinson´s disease. The main questions it aims to answer are:

1. Is retinal vessel oxyhemoglobin saturation and vessel width altered in people with Parkinson´s disease?
2. Is the thickness of the retinal nerve fiber layer altered in people with Parkinson´s disease?
3. Is the response of ganglion cells of the inner retina and the visual cortex altered in people with Parkinson´s disease?

The study procedure is threefold. The participants will:

A. Sit in front of a screen and focus on a red dot of its middle. A simple recording electrodes are applied on the cornea, forehead and scalp for the electrophysiological measurements. Prior to this procedure a topical anesthetic gel is applied to numb the eye to prevent discomfort from placement of the corneal electrodes.

B. Undergo general eye examination and optical coherence tomography (OCT) to measure the retinal tissue thickness. Prior to eye examination,eye drops are applied into the eyes to enlarge the pupils C. Sit in front of a fundus camera for obtaining images of the retinal vessels to measure oxygen saturation and the vessel width

Researchers will compare the obtained measurements with age- and gender matching of healthy controls.

Inclusion Criteria:

• Confirmed Parkinson Disease

Exclusion Criteria:

• Eye disease
• Diabetic Mellitus
• Chronic Obstructive Pulmonary Disease (COPD)
• Other Neurological Disease
• Smoking on a daily basis

People with confirmed parkinsons disease Stage 0-3 on the Hohen and Yahr scale