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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Date data sharing statement initially provided
Type of registration
Prospectively registered

Titles & IDs
Public title
How caffeine affects the visual brain
Scientific title
Effect of caffeine on visual neuroplasticity in young healthy adults
Secondary ID [1] 300707 0
ARC Discovery Project DP180102596
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Vision impairment 316521 0
Condition category
Condition code
Neurological 314766 314766 0 0
Studies of the normal brain and nervous system
Eye 314819 314819 0 0
Normal eye development and function

Study type
Description of intervention(s) / exposure
Twenty healthy young (18-35 years) adults will be recruited and screened to ensure healthy eyes and vision. The screening includes a visual acuity test, determination of spectacle prescription, and brief ocular health examination.

The main task is a measure of ocular dominance, where observers will look at patterns on a computer monitor and make judgments (by pressing a button) about the colour of a pattern that alternates between red and green. Both eyes need to be open (blinking allowed) during the main task for ocular dominance to be measured.

There will be two test sessions, a treatment session and control session. The order of the sessions will be randomised and the participants blinded to the treatment. Participants will be instructed not to consume caffeine for 12 hours prior to attending each test session. At the beginning of each test session, participants will undergo baseline testing of the main ocular dominance task (15 minutes). This will be followed by:

(1) a controlled dose of caffeine in the form of a single ‘No Doz Plus’ pill, which consists of 100 mg caffeine, 10 mg thiamine hydrochloride (Vitamin B1) and 10 mg nicotinic acid (Vitamin B3), or

(2) a placebo pill (single ‘Betamin’ pill, which consists of 100 mg thiamine hydrochloride (Vitamin B1).

Participants will wait 30 minutes for the pill to reach its peak effect, and then the participant's dominant eye will be patched for 90 minutes. Post-patching ocular dominance tests (repeat of baseline tests, 15 minutes) will be conducted at the end of the session. During the 120 minutes of waiting, participants will be asked to sit quietly in a room and can undertake activities such as reading, watching a movie, or working on a laptop.

At the second visit at least one week later, participants will undergo the same protocol (caffeine washout, baseline ocular dominance testing, tablet ingestion, patching of dominant eye, post-tablet ocular dominance testing) such that all participants will have consumed both the caffeine pill and placebo pill. The pills are both white, uncoated, round tablets with no engravings of approximately the same size, which will assist in masking the identity of the pill at each test session.
Intervention code [1] 317031 0
Treatment: Drugs
Comparator / control treatment
As a comparator/control treatment, participants will consume a pure vitamin pill (1 x ‘Betamin’ tablets, which consists of 100 mg thiamine or Vitamin B1),
Control group

Primary outcome [1] 323118 0
Participants will observe a small striped patch in the middle of a computer monitor and make judgments (by pressing a button) about the colour of the pattern, as it alternates between red and green. The change in ocular dominance will be calculated, which compares the relative colour judgments before and after treatment.
Timepoint [1] 323118 0
Baseline (prior to treatment) compared to 120 minutes post-tablet ingestion and eye patching
Secondary outcome [1] 380851 0
Timepoint [1] 380851 0

Key inclusion criteria
1) Visual acuity at least 6/7.5 in both eyes
2) Good general health
Minimum age
18 Years
Maximum age
35 Years
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
1) Contraindications for No Doz consumption: high blood pressure, recent heart attack, abnormal heart rhythm, stomach ulcer, inflamed colon and small intestine, severe liver disease, seizures, chronic insomnia, moderate to severe kidney impairment
2) Medications with possible interactions with No Doz and/or Vitamin B: tizanidine (muscle relaxant), digoxin (used to treat heart conditions), diuretics (particularly loop diuretics like furosemide), and phenytoin (used to treat epilepsy).

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
All participants receive all the interventions (two) in random order during the study.
The random order is assigned by a study coordinator.
Examiners and participants are blinded.
The allocation is concealed by numbered containers.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Simple randomisation using a randomisation table created by computer software (i.e. computerised sequence generation) to allocate either 1st or 2nd treatment as first session.
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?
The people receiving the treatment/s
The people administering the treatment/s
The people assessing the outcomes
Intervention assignment
Other design features
Phase 4
Type of endpoint(s)
Statistical methods / analysis
We will recruit 20 healthy, young (18-35 years) observers. The effect of caffeine is believed to result in a similar change in brain neurochemical levels as that seen after ingestion of donepezil. Our research hypothesis is based on a recently published study (Sheynin et al Front Neurosci 2019; 13: 22) that tested the effect on short term monocular deprivation after donepezil in 12 healthy, young observers (mean age 23 years), compared to a placebo. Based on the mean (M=-1.27) and standard deviation (SD=-0.5) of the difference observed between intervention and placebo in that study, a sample size of 5 (paired t-test) would achieve a power of 80% at a significance level of 5% (two-sided). We have increased our sample size to 20, to account for possible attrition in participant numbers and to achieve a conservative estimate of effect size (Cohen’s d=0.7). Data will be analysed using appropriate statistical methods (ANOVA, paired t-tests) in a statistical package.

Recruitment status
Not yet recruiting
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment in Australia
Recruitment state(s)
Recruitment postcode(s) [1] 29569 0
3010 - University Of Melbourne

Funding & Sponsors
Funding source category [1] 305152 0
Government body
Name [1] 305152 0
Australian Research Council Discovery Project DP180102596
Address [1] 305152 0
GPO Box 2702, Canberra ACT 2601
Country [1] 305152 0
Primary sponsor type
The University of Melbourne
Department of Optometry and Vision Sciences
The University of Melbourne VIC 3010 Australia
Secondary sponsor category [1] 305510 0
Name [1] 305510 0
Address [1] 305510 0
Country [1] 305510 0

Ethics approval
Ethics application status
Ethics committee name [1] 305518 0
University of Melbourne Human Research Ethics Committee
Ethics committee address [1] 305518 0
Office for Research Ethics and Integrity
Level 3, 780 Elizabeth Street
The University of Melbourne VIC 3010 Australia
Ethics committee country [1] 305518 0
Date submitted for ethics approval [1] 305518 0
Approval date [1] 305518 0
Ethics approval number [1] 305518 0

Brief summary
Caffeine is readily available and widely consumed by adults of all ages. We are interested in whether temporarily manipulating caffeine levels (from complete washout to a controlled dose of caffeine) has an effect on ocular dominance in healthy adults. Specifically, we are testing its effect on a vision test that is frequently used to indirectly measure changes in brain function. If caffeine indeed influences our test results, then future studies may need to control caffeine consumption.
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 100646 0
Dr Bao Nguyen
Address 100646 0
C/O Department of Optometry and Vision Sciences
The University of Melbourne VIC 3010 Australia
Country 100646 0
Phone 100646 0
+61 3 9035 8553
Fax 100646 0
Email 100646 0
Contact person for public queries
Name 100647 0
Dr Bao Nguyen
Address 100647 0
C/O Department of Optometry and Vision Sciences
The University of Melbourne VIC 3010 Australia
Country 100647 0
Phone 100647 0
+61 3 9035 8553
Fax 100647 0
Email 100647 0
Contact person for scientific queries
Name 100648 0
Dr Bao Nguyen
Address 100648 0
C/O Department of Optometry and Vision Sciences
The University of Melbourne VIC 3010 Australia
Country 100648 0
Phone 100648 0
+61 3 9035 8553
Fax 100648 0
Email 100648 0

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
No/undecided IPD sharing reason/comment
Individual participant data will not be shared as all individual participant data collected during the trial will, after de-idenfication, be pooled for analysis and publication.
What supporting documents are/will be available?
No other documents available
Summary results
No Results