Brain Dopamine Biomarker

NCT07748715 | Not Yet Recruiting FDA Drug

• 1 other identifier: STUDY010037
• Study Type: observational
• Target: 50
• Locations: 0 countries
• Sites: N/A

Brief Summary

This study is being conducted at the Morsani College of Medicine to determine whether signals recorded from the eyes and brain can be used as a noninvasive way to monitor dopamine function. Approximately 50 adults (25 with Parkinson's disease and 25 without Parkinson's disease) will participate. Participants will undergo electroretinography (ERG) and electroencephalography (EEG), which are FDA-approved, noninvasive devices that measure electrical activity from the retina and brain using sensors placed on the skin around the eyes and scalp. Participants with Parkinson's disease will be tested before and after taking their prescribed Parkinson's medication (e.g., Sinemet® \[carbidopa/levodopa\]). Participants without Parkinson's disease will receive a single dose of compounded levodopa/carbidopa eye drops (an FDA-approved drug used in an unapproved ophthalmic formulation) in one eye and a placebo eye drop in the other eye. The placebo consists of the same vehicle solution without levodopa/carbidopa and contains 0.1% ascorbic acid, 0.001% benzalkonium chloride, and phosphate-buffered saline. Randomization will be used to determine which eye receives the levodopa/carbidopa eye drop and which eye receives the placebo. Researchers will compare measurements obtained before and after treatment to evaluate whether blue-light visual responses are associated with dopamine activity.

Conditions

Parkinson Disease; Healthy Adult Participants

Keywords

dopamine; retina; biomarker; brain; electroretinography; blue light

Outcome Measures

Primary Outcomes (1)

• Electroretinography

  Electroretinography (ERG) is used to diagnose and evaluate the conditions of the retina and optic nerve, including photoreceptors and ganglion cells, by measuring the electrical activity generated by retinal cells in response to light stimulus. The ERG will be performed using the FDA-approved RETeval® device.

  2 measurements separated by 1 hour

Secondary Outcomes (1)

• Electroencephalography

  2 measurements separated by 1 hour

Study Arms (2)

Healthy controls

Adults (18+ years) with no underlying eye conditions that would affect blue light transmission

Drug: Levadopa/Carbidopa eyedrops; Other: Sham

Parkinsons

As the Parkinson's patients self-administer dopaminergic medication, we will use this regular event of dopamine influx as a vehicle to measure changes in dopamine transmission in the eye.

Drug: Levodopa/Carbidopa (Sinemet)

Interventions

Levadopa/Carbidopa eyedrops DRUG

Topical levodopa/carbidopa eyedrops (1.4/0.34 microM) in a base of 0.1% w/v ascorbic acid and 0.001% w/v benzalkonium chloride dissolved in 1× phosphate-buffered saline.

Healthy controls

Sham OTHER

The vehicle (control) solution will consist of 0.1% w/v ascorbic acid and 0.001% w/v benzalkonium chloride dissolved in 1× phosphate-buffered saline.

Healthy controls

Levodopa/Carbidopa (Sinemet) DRUG

Parkinson's patients will self-administer their medication and measurements will be taken prior to and 15-30 minutes after self-administration.

Parkinsons

Eligibility Criteria

• Age: 18 Years+
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)
• Sampling Method: Probability Sample

Study Population

Adults ages 18 years and above. Adults will be either healthy controls or have confirmed diagnosis of Parkinson's disease.

You may qualify if:

• Parkinson's subjects will have received physician verified diagnosis of the disease and be on a dopaminergic medication for at least 3 months

You may not qualify if:

• Any movement, strength, or balance assessments that may pose a potential risk for injury
• Individuals with a history of photosensitive epilepsy or seizure activity triggered by visual stimuli
• Current use of antipsychotics, stimulants, or other medications known to affect central dopaminergic transmission
• Pregnancy
• Recent ocular surgery
• Phenylketonuria
• (PD participants) not cognitively intact and not able to consent for themselves
• (non-PD subjects) a pre-screening survey will assess medication use and neurological history
• Ophthalmologic or visual system conditions that may interfere with stimulus delivery or retinal function. These include significant cataract (defined as LOCS III ≥ NC2/NO2 or any media opacity that precludes adequate delivery of visual stimuli to the retina), active retinal or macular pathology (including age-related macular degeneration with significant drusen or geographic atrophy, diabetic retinopathy, retinal vein occlusion, or epiretinal membrane with foveal involvement), glaucoma, or any optic neuropathy.
• Individuals with congenital color vision deficiencies, particularly tritan-spectrum defects
• Ocular surgery within the past three months
• Use of medications known to affect retinal electrophysiology (e.g., chronic hydroxychloroquine, vigabatrin, deferoxamine, or isotretinoin)
• History of photosensitive epilepsy or visually triggered seizures (especially relevant given the use of bright visual stimuli and potential flicker paradigms)

Sponsors & Collaborators

• University of South Florida: lead
• Center for Neuromusculoskeletal Research: collaborator

Related Publications (23)

• Perlman I, Kondo M, Chelva E, Robson AG, Holder GE. ISCEV extended protocol for the S-cone ERG. Doc Ophthalmol. 2020 Apr;140(2):95-101. doi: 10.1007/s10633-019-09730-6. Epub 2019 Nov 20.

  PMID: 31749034 BACKGROUND

• Sisco SM, Slonena E, Okun MS, Bowers D, Price CC. Parkinson's disease and the Stroop color word test: processing speed and interference algorithms. Clin Neuropsychol. 2016 Oct;30(7):1104-17. doi: 10.1080/13854046.2016.1188989. Epub 2016 Jun 6.

  PMID: 27264121 BACKGROUND

• Diaz-Santos M, Cao B, Yazdanbakhsh A, Norton DJ, Neargarder S, Cronin-Golomb A. Perceptual, cognitive, and personality rigidity in Parkinson's disease. Neuropsychologia. 2015 Mar;69:183-93. doi: 10.1016/j.neuropsychologia.2015.01.044. Epub 2015 Jan 30.

  PMID: 25640973 BACKGROUND

• Soto Linan V, Rioux V, Peralta M 3rd, Dupre N, Hebert M, Levesque M. Early detection of Parkinson's disease: Retinal functional impairments as potential biomarkers. Neurobiol Dis. 2025 May;208:106872. doi: 10.1016/j.nbd.2025.106872. Epub 2025 Mar 14.

  PMID: 40090470 BACKGROUND

• Nowacka B, Lubinski W, Honczarenko K, Potemkowski A, Safranow K. Bioelectrical function and structural assessment of the retina in patients with early stages of Parkinson's disease (PD). Doc Ophthalmol. 2015 Oct;131(2):95-104. doi: 10.1007/s10633-015-9503-0. Epub 2015 May 14.

  PMID: 25972299 BACKGROUND

• Langheinrich T, Tebartz van Elst L, Lagreze WA, Bach M, Lucking CH, Greenlee MW. Visual contrast response functions in Parkinson's disease: evidence from electroretinograms, visually evoked potentials and psychophysics. Clin Neurophysiol. 2000 Jan;111(1):66-74. doi: 10.1016/s1388-2457(99)00223-0.

  PMID: 10656512 BACKGROUND

• Ikeda H, Head GM, Ellis CJ. Electrophysiological signs of retinal dopamine deficiency in recently diagnosed Parkinson's disease and a follow up study. Vision Res. 1994 Oct;34(19):2629-38. doi: 10.1016/0042-6989(94)90248-8.

  PMID: 7975301 BACKGROUND

• Gottlob I, Schneider E, Heider W, Skrandies W. Alteration of visual evoked potentials and electroretinograms in Parkinson's disease. Electroencephalogr Clin Neurophysiol. 1987 Apr;66(4):349-57. doi: 10.1016/0013-4694(87)90032-0.

  PMID: 2435514 BACKGROUND

• Frishman L, Sustar M, Kremers J, McAnany JJ, Sarossy M, Tzekov R, Viswanathan S. ISCEV extended protocol for the photopic negative response (PhNR) of the full-field electroretinogram. Doc Ophthalmol. 2018 Jun;136(3):207-211. doi: 10.1007/s10633-018-9638-x. Epub 2018 May 31.

  PMID: 29855761 BACKGROUND

• Giza E, Fotiou D, Bostantjopoulou S, Katsarou Z, Karlovasitou A. Pupil light reflex in Parkinson's disease: evaluation with pupillometry. Int J Neurosci. 2011 Jan;121(1):37-43. doi: 10.3109/00207454.2010.526730. Epub 2010 Nov 1.

  PMID: 21034369 BACKGROUND

• Micieli G, Tassorelli C, Martignoni E, Pacchetti C, Bruggi P, Magri M, Nappi G. Disordered pupil reactivity in Parkinson's disease. Clin Auton Res. 1991 Mar;1(1):55-8. doi: 10.1007/BF01826058.

  PMID: 1821667 BACKGROUND

• Tabashum T, Zaffer A, Yousefzai R, Colletta K, Jost MB, Park Y, Chawla J, Gaynes B, Albert MV, Xiao T. Detection of Parkinson's Disease Through Automated Pupil Tracking of the Post-illumination Pupillary Response. Front Med (Lausanne). 2021 Mar 25;8:645293. doi: 10.3389/fmed.2021.645293. eCollection 2021.

  PMID: 33842509 BACKGROUND

• Maskin MB, Riklan M, Chabot D. Effects of "short-term" versus "long-term" L-Dopa therapy in parkinsonism on critical flicker frequency. Percept Mot Skills. 1974 Apr;38(2):455-8. doi: 10.2466/pms.1974.38.2.455. No abstract available.

  PMID: 4363091 BACKGROUND

• Sabeti F, Thomson K, Maddess T, Karouta C, Leung M, Anstice N, Jong T, Ashby R. Retinal Function in Young Adults Following Topical Application of Levodopa to the Eye. Transl Vis Sci Technol. 2024 Oct 1;13(10):12. doi: 10.1167/tvst.13.10.12.

  PMID: 39374001 BACKGROUND

• Lee H, Scott J, Griffiths H, Self JE, Lotery A. Oral levodopa rescues retinal morphology and visual function in a murine model of human albinism. Pigment Cell Melanoma Res. 2019 Sep;32(5):657-671. doi: 10.1111/pcmr.12782. Epub 2019 Apr 2.

  PMID: 30851223 BACKGROUND

• Thomson K, Morgan I, Karouta C, Ashby R. Levodopa inhibits the development of lens-induced myopia in chicks. Sci Rep. 2020 Aug 6;10(1):13242. doi: 10.1038/s41598-020-70271-z.

  PMID: 32764736 BACKGROUND

• Thomson K, Karouta C, Morgan I, Kelly T, Ashby R. Effectiveness and safety of topical levodopa in a chick model of myopia. Sci Rep. 2019 Dec 4;9(1):18345. doi: 10.1038/s41598-019-54789-5.

  PMID: 31797988 BACKGROUND

• Thomson K, Karouta C, Sabeti F, Anstice N, Leung M, Jong T, Maddess T, Morgan IG, Game J, Ashby R. The safety and tolerability of levodopa eye drops for the treatment of ocular disorders: A randomized first-in-human study. Clin Transl Sci. 2022 Nov;15(11):2673-2684. doi: 10.1111/cts.13392. Epub 2022 Oct 11.

  PMID: 36221799 BACKGROUND

• Nelson CA, Obray JD, Roll CR, Williams PE, Smith KJ, Harris WT, Hafen CW, Burris MD, Manwaring KH, Adams DN, Weber KS, Hope S, Mitchell UH, Yorgason JT, Steffensen SC. Leukocytic Dopamine D2 Receptors as Biomarkers for Brain Dopamine Levels in Parkinson Disease. Am J Pathol. 2026 May;196(5):1188-1204. doi: 10.1016/j.ajpath.2026.01.003. Epub 2026 Feb 1.

  PMID: 41633447 BACKGROUND

• Volkow ND, Wang GJ, Telang F, Fowler JS, Logan J, Jayne M, Ma Y, Pradhan K, Wong C. Profound decreases in dopamine release in striatum in detoxified alcoholics: possible orbitofrontal involvement. J Neurosci. 2007 Nov 14;27(46):12700-6. doi: 10.1523/JNEUROSCI.3371-07.2007.

  PMID: 18003850 BACKGROUND

• Krabbe S, Duda J, Schiemann J, Poetschke C, Schneider G, Kandel ER, Liss B, Roeper J, Simpson EH. Increased dopamine D2 receptor activity in the striatum alters the firing pattern of dopamine neurons in the ventral tegmental area. Proc Natl Acad Sci U S A. 2015 Mar 24;112(12):E1498-506. doi: 10.1073/pnas.1500450112. Epub 2015 Feb 9.

  PMID: 25675529 BACKGROUND

• Petrie JA, Trikha A, Lundberg HL, Bills KB, Manwaring PK, Obray JD, Adams DN, Brown BL, Fleming DE, Steffensen SC. Sex-Specific Electrocortical Interactions in a Color Recognition Task in Men and Women with Opioid Use Disorder. Biomedicines. 2025 Dec 8;13(12):3002. doi: 10.3390/biomedicines13123002.

  PMID: 41463014 BACKGROUND

• Petrie J, Kowallis LR, Kamhout S, Bills KB, Adams D, Fleming DE, Brown BL, Steffensen SC. Gender-Specific Interactions in a Visual Object Recognition Task in Persons with Opioid Use Disorder. Biomedicines. 2023 Sep 5;11(9):2460. doi: 10.3390/biomedicines11092460.

  PMID: 37760905 BACKGROUND

Related Links

• LKC Technologies - RETeval

MeSH Terms

Conditions

Parkinson Disease

Interventions

salicylhydroxamic acid; Levodopa; Carbidopa; carbidopa, levodopa drug combination

Condition Hierarchy (Ancestors)

Parkinsonian Disorders; Basal Ganglia Diseases; Brain Diseases; Central Nervous System Diseases; Nervous System Diseases; Movement Disorders; Synucleinopathies; Neurodegenerative Diseases

Intervention Hierarchy (Ancestors)

Dihydroxyphenylalanine; Catecholamines; Amines; Organic Chemicals; Catechols; Phenols; Benzene Derivatives; Hydrocarbons, Aromatic; Hydrocarbons, Cyclic; Hydrocarbons; Phenylalanine; Amino Acids, Aromatic; Amino Acids, Cyclic; Amino Acids; Amino Acids, Peptides, and Proteins; Tyrosine; Methyldopa; Hydrazines

Study Officials

• Nathan D Schilaty, DC, PhD

  University of South Florida

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Nathan D Schilaty, DC, PhD

CONTACT

813-974-1377; nschilaty@usf.edu

Madison A Kagin, BA

CONTACT

813-974-1112; makagin@usf.edu

Study Design

• Study Type: observational
• Observational Model: COHORT
• Time Perspective: PROSPECTIVE
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: July 31, 2026
• First Posted: August 6, 2026
• Study Start (Estimated): October 1, 2026
• Primary Completion (Estimated): September 30, 2027
• Study Completion (Estimated): September 30, 2027
• Last Updated: August 6, 2026

Record last verified: 2026-07

Data Sharing

• IPD Sharing: Will not share