The purpose of this study is to examine if a correlation exists between findings from brain imaging studies of the status of the dopamine system in the brain using DaTscan and SPECT imaging, clinical symptoms of Parkinson's disease, and changes in the structure of the retina as detected by optical coherence tomography (OCT) in recently diagnosed and more advanced Parkinson's disease patients.

Inclusion Criteria:

1. Willing and able to give informed consent.

2. Between the ages of 50-80 years old.

3. Male or female with idiopathic PD who fulfill UK PD Society brain bank criteria for diagnosis of Parkinson's disease.

4. Early stage subjects will need to have Unified Parkinson's Disease Rating Scale (UPDRS) motor scores of < 10, be within 3 years of diagnosis, and not requiring dopaminergic therapy

5. Later stage subjects will need to have Unified Parkinson's Disease Rating Scale motor scores of > 20 and be > 5 years from diagnosis

6. If female, one of the following three scenarios must apply:

   • at least two years post-menopausal
   • surgically sterile
   • negative urine pregnancy test, and following a reliable method of birth control (oral contraceptive, intrauterine device, contraceptive implant, barrier, or abstinence) for at least two months prior to entry, and agreeing both to follow a reliable method of birth control, and (if relevant) to desist from breast feeding during, and for two weeks following tracer administration.

Exclusion Criteria:

1. Abrupt onset of Parkinsonism
2. 'Other Parkinson-like syndromes (e.g. progressive supranuclear palsy, multiple system atrophy)
3. Any condition that would preclude successful completion of SPECT scanning
4. Use of anti-coagulant therapy
5. Any clinically significant eye disease that would complicate interpretation of OCT data
6. Use of any drugs that would alter or interfere with tracer binding for SPECT imaging studies (ex., cocaine, amphetamines, methylphenidate, ephedrine, phentermine, bupropion, fentanyl, selective serotonin reuptake inhibitors).
7. Known sensitivity to the imaging agent or to Lugol's solution or to potassium perchlorate.
8. History or presence of severe renal disease.

The study population will be Parkinson's disease patients (Hoehn and Yahr stage 1 - 3). One study group will be subjects (N = 6) with early PD who will be within 3 years from diagnosis and not requiring dopaminergic therapy. These subjects will need to have Unified Parkinson's Disease Rating Scale motor scores of 10 - 15. The second study group will be subjects (N = 6) with more advanced PD and will have had PD for at least 5 years and will need to have Unified Parkinson's Disease Rating Scale motor scores of > 20.