Table 2 Inclusion and exclusion criteria

Diagnosis of PD according to the UKPDSBB criteria

Hoehn and Yahr Parkinson’s staging score ≥ 4

The patient must be able and willing to give written informed consent

Secondary cause of parkinsonism as detected by history (e.g. drug-induced parkinsonism)

The patient must be willing to participate in all study related activities and visits

Secondary cause of parkinsonism as detected by investigation (e.g. vascular parkinsonism as detected by neuroimaging)

Age of onset Parkinson’s disease > 30 years

Dementia according to DSM-IV

Stable doses of Parkinson medications ≥4 weeks

Major depressive disorder according to DSM-IV

Current age ≥ 60 years

Psychotic disorder(s) according to DSM-IV

Prior brain surgery (except deep brain stimulation)

Previous eye surgery (except phacoemulsification for cataract and artificial lenses)

Blindness in 1 eye

Medication that influences normal visual function other than PD medication. (Detailed information, please see Additional file 2: Appendix 2)

Systemic diseases that may cause eye problems (HIV, DM type I, type II if the patient had ophthalmologic therapy and/or abnormalities at last screening)

Neurodegenerative diseases other than Parkinson’s disease

History of lesions near the optic chiasm or occipital cortex

Migraine