Investigating the Effect of Caffeine and Alcohol on Pupil Dynamics
Investigating the Effect of Caffeine and Alcohol on Pupil Dynamics (PAC)
National University of Singapore
100 participants
Jun 1, 2026
INTERVENTIONAL
Conditions
Summary
The goal of this study is to understand how caffeine and alcohol affect the ocular and physiological systems, especially how the pupil (the aperture in the colored part of the eye) responds to light. It will also test whether these changes can be used to detect recent caffeine or alcohol intake using a portable eye device. The main questions it aims to answer are: 1. How does caffeine change pupil responses, eye movements, and other ocular and physiological measurements? 2. How does alcohol change these same ocular and physiological responses? 3. Are the effects of caffeine and alcohol different from each other? 4. Can these changes be used to accurately identify whether someone has consumed caffeine or alcohol? Researchers will compare caffeine, alcohol, and a placebo (a look-alike drink with no active substance) to see how each affects the ocular and physiological outcomes. Participants will: 1. Attend three separate sessions where they will consume caffeine, alcohol, or a placebo (in random order) 2. Undergo pupillary response evaluation using a handheld device that measures responses to different colored light stimuli 3. Have their eye movements analyzed 4. Have retinal and choroidal thickness, blood perfusion, and ocular oxygen levels measured 5. Have basic body measurements recorded (such as pulse rate and blood pressure) 6. Complete tests at multiple time points over 2 hours after consumption The results of this study may help develop a quick and non-invasive way to detect recent caffeine or alcohol use for clinical and safety purposes.
Eligibility
Inclusion Criteria4
- Age: 30 to 50 years of age
- Visual Acuity: Best Corrected Visual Acuity (BCVA) of 0.20 LogMAR or better in both eyes
- Ability to provide informed consent: Participants must be able to understand and sign the informed consent form
- Ability to consume both caffeine and alcohol: Participants must be willing and able to consume caffeine and alcohol as part of the study
Exclusion Criteria15
- Diagnosed ocular conditions: Participants with ocular or ocular movement diseases such as glaucoma, age-related macular degeneration, diabetic retinopathy, amblyopia, severe ptosis, or conditions relating to pupils: anisocoria, irregular pupil, Adie tonic, Horner's syndrome, Argyll Robertson pupil, etc. These exclude cataracts, refractive errors, and any ocular condition not affecting vision or ocular movement or obstructing the pupil.
- Diagnosed and unresolved neurological conditions:Stroke, unresolved traumatic brain injury, space-occupying lesions in the brain, neuropathies, demyelinating conditions, nerve palsies, etc.
- Diagnosed systemic conditions that may restrict the participant from drinking caffeine or alcohol: Hypertension, cardiovascular disease, liver disease, kidney disease, etc.
- Medications: Participants taking any medications that may interact with caffeine or alcohol, affect alertness, or cause drowsiness
- Previous complex intraocular eye surgery: Participants who have undergone any eye surgery other than uncomplicated refractive surgery.
- Pregnancy or breastfeeding: Pregnant or breastfeeding women will be excluded from the study, as caffeine and alcohol can affect the fetus or baby
- History of substance abuse: Participants with a history of substance abuse
- Allergies or sensitivities: Participants with allergies or sensitivities to caffeine or alcohol
- Shift work or having travelled across 2 time zones over the past 2 weeks: This is essential to avoid any impact of sleep deprivation on our outcome measures
- Non-consumers or light-consumers of caffeine and alcohol Participants who are light consumers of caffeine or alcohol will be excluded due to higher sensitivity to side effects.
- Caffeine: If less than 100 mg of caffeine per week from all sources (including coffee, soft drinks, energy drinks, chocolate, and medications) based on the CCQ* Alcohol: If AUDIT-C** score less than 1
- - Extremely frequent consumers Participants who are extremely frequent consumers of caffeine or alcohol will be excluded due to potential withdrawal symptoms during the required 18-hour abstinence and possible reduced sensitivity to administered doses.
- Caffeine: If more than 400mg of caffeine (e.g., 5 espressos) per day from all sources (including coffee, soft drinks, energy drinks, chocolate, and medications) based on the CCQ* Alcohol: If AUDIT-C** scores more than 4 for men and more than 3 for women
- *CCQ: Caffeine Consumption Questionnaire
- **AUDIT-C: Alcohol Use Disorders Identification Test-C
Interested in this trial?
Get notified about updates and connect with the research team.
Interventions
Participants receive a matched placebo tablet together with a non-alcoholic beverage identical in appearance and volume to the active conditions. A cornstarch-based formulation may be used for the placebo tablet. Beverage presentation is standardized to maintain blinding across study conditions. No active caffeine or alcohol is administered.
Participants receive a single oral dose of caffeine (\~3 mg/kg body weight) administered in tablet form. The caffeine is given with a non-alcoholic beverage matched to study conditions. All procedures are performed under randomized, double-masked crossover design conditions.
Participants consume a standardized alcoholic beverage designed to achieve a target blood alcohol concentration of approximately 0.05%. A placebo tablet is administered alongside the beverage to maintain masking. All procedures are performed under randomized, double-masked crossover design conditions.
Locations(1)
View Full Details on ClinicalTrials.gov
For the most up-to-date information, visit the official listing.
NCT07625358