We are experiencing 4 week turn-around time in review of submissions and resubmissions. We recommend commencing this process concurrently with your ethics submission and allowing at least 8 weeks for registration to be completed from date of first submission. We currently do not have the capacity to expedite reviews.

Note also there are delays to review of updates. We appreciate your patience.

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been endorsed by the ANZCTR. Before participating in a study, talk to your health care provider and refer to this information for consumers
Trial registered on ANZCTR

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

Titles & IDs
Public title
Does caffeine consumption influence visual performance?
Scientific title
Effect of caffeine on a visual contrast perception task in young healthy adults
Secondary ID [1] 288889 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Vision impairment 298194 0
Condition category
Condition code
Neurological 298353 298353 0 0
Studies of the normal brain and nervous system

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 main task is to observe patterns on a computer monitor and make judgments (by pressing a button) about the contrast of a pattern. 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 visual testing. This will be followed by 1) a controlled dose of caffeine in the form of an over-the-counter caffeine + vitamin pill (2 x ‘No Doz Plus’ tablets = 200 mg caffeine + 20 mg thiamine or Vitamin B1 + 20 mg nicotinic acid or Vitamin B3) or 2) a placebo pill. Visual testing will then occur 45 minutes after tablet ingestion. At the second visit at least one week later, participants will undergo the same protocol (caffeine washout, baseline testing, tablet ingestion, post-tablet 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] 294346 0
Treatment: Drugs
Comparator / control treatment
As a comparator/control treatment, participants will consume a pure vitamin pill (2 x ‘Betamin’ tablets = 200 mg thiamine or Vitamin B1),
Control group

Primary outcome [1] 297829 0
Participants will observe a small circular striped patch in the middle of a computer monitor and make judgments (by pressing a button) about the contrast of the pattern. A 'suppression index' will be calculated that compares the contrast judgment before and after treatment.
Timepoint [1] 297829 0
Baseline (prior to treatment) compared to 45 minutes post-tablet ingestion
Secondary outcome [1] 322356 0
Timepoint [1] 322356 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 previous study (Kosovicheva et al Front Behav Neurosci 2012;6:61) that measured the effect of donepezil on visual performance in a group of healthy, young observers (mean age 26 years), compared to a placebo pill. In that study, a paired t-test (drug vs placebo) found a significant difference in performance following ingestion of donepezil (group mean difference = 1% contrast, standard deviation = 1.3% contrast) in a group of 19 individuals (alpha = 0.05, 2-tailed) with 90% power, rejecting the null hypothesis that the mean difference was 0% contrast. We have rounded this up to 20 participants in each group to find intra-individual differences in visual performance with and without caffeine ingestion.

Data will be analysed using appropriate statistical methods (ANOVA, paired t-tests) in a statistical package.

Recruitment status
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] 12994 0
3010 - University Of Melbourne

Funding & Sponsors
Funding source category [1] 293241 0
Government body
Name [1] 293241 0
Australian Research Council Discovery Project DP140100157
Address [1] 293241 0
GPO Box 2702, Canberra ACT 2601
Country [1] 293241 0
Primary sponsor type
The University of Melbourne
Department of Optometry and Vision Sciences
Level 4 Alice Hoy Building (Building 162) Monash Road
The University of Melbourne, Parkville VIC 3010 Australia
Secondary sponsor category [1] 292043 0
Name [1] 292043 0
Address [1] 292043 0
Country [1] 292043 0

Ethics approval
Ethics application status
Ethics committee name [1] 294719 0
University of Melbourne Human Research Ethics Committee
Ethics committee address [1] 294719 0
Office for Research Ethics and Integrity
Level 3, 780 Elizabeth Street
The University of Melbourne, Parkville VIC 3010
Ethics committee country [1] 294719 0
Date submitted for ethics approval [1] 294719 0
Approval date [1] 294719 0
Ethics approval number [1] 294719 0
HREC #1646382

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 visual perception in healthy adults. Specifically, we are testing its effect on a contrast judgment task (is one stripey pattern higher in contrast than another?) that our laboratory frequently uses to indirectly measure changes in brain function that occur with normal ageing or in conditions such as migraine. If caffeine indeed influences our test results, then future studies may need to control caffeine consumption.
Trial website
Trial related presentations / publications
Public notes
This project is being conducted as a student group research project as part of the 2nd year Doctor of Optometry subject: Research Studies in Vision and Optometry (OPTO90025) at the University of Melbourne. This is a group research project and all the students (listed as investigators) are involved in participant recruitment and testing under supervision.

Principal investigator
Name 64318 0
Dr Bao Nguyen
Address 64318 0
Department of Optometry and Vision Sciences
Level 4 Alice Hoy Building (Building 162) Monash Road
The University of Melbourne, Parkville VIC 3010
Country 64318 0
Phone 64318 0
+61 3 9035 9979
Fax 64318 0
Email 64318 0
Contact person for public queries
Name 64319 0
Dr Bao Nguyen
Address 64319 0
Department of Optometry and Vision Sciences
Level 4 Alice Hoy Building (Building 162) Monash Road
The University of Melbourne, Parkville VIC 3010
Country 64319 0
Phone 64319 0
+61 3 9035 9979
Fax 64319 0
Email 64319 0
Contact person for scientific queries
Name 64320 0
Dr Bao Nguyen
Address 64320 0
Department of Optometry and Vision Sciences
Level 4 Alice Hoy Building (Building 162) Monash Road
The University of Melbourne, Parkville VIC 3010
Country 64320 0
Phone 64320 0
+61 3 9035 9979
Fax 64320 0
Email 64320 0

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
No/undecided IPD sharing reason/comment
What supporting documents are/will be available?
Summary results
Have study results been published in a peer-reviewed journal?
Journal publication details
Publication date and citation/details [1] 7230 0
Nguyen B.N., Hew S., Ly J., Shin H., Wong J.C., Yeung E., McKendrick A.M. (2018) “Acute caffeine ingestion affects surround suppression of perceived contrast.” Journal of Psychopharmacology 32(1): 81-88 doi:10.1177/0269881117725684
Attachments [1] 7230 0
Other publications
Have study results been made publicly available in another format?
Results – basic reporting
Results – plain English summary