Inclusion Criteria:

• 1. Parkinson's disease (H\&Y 1, 2, and 3) confirmed by pretest administration of the UPDRS,
• 2. 55-90 years of age,
• 3. Montreal Cognitive Assessment \> 17.

Exclusion Criteria:

• 1. Uncontrolled cardiovascular or neuromuscular diseases that prevent participation in a training program;
• 2. cerebrovascular disease;
• 3. documented HIV infection or other immunodeficiency syndrome;
• 4. any systemic inflammatory or autoimmune conditions such as rheumatoid arthritis, systemic lupus erythematosus, or other serious concomitant medical illness;
• 5. a history of ocular surgeries (except for cataract surgery more than 6 months ago) or other ocular diseases;
• 6. bilateral moderate or severe cataracts;
• 7. refractive errors of myopia, hyperopia and/or astigmatism more than 6.0 Diopters.