Does Caffeine or Alcohol Change Pupil Reactions? A Test in Healthy Adults

Is this trial a fit for you?

A plain-English reading of the study's rules. Only the study team can confirm whether you qualify.

What this trial studies

This is a randomized, double-masked, within-subject crossover study in 100 healthy adults aged 30 to 50. Each participant experiences three sessions—caffeine, alcohol, and placebo—in random order, with measurements of pupil dynamics, eye movements, and retinal function using chromatic pupillometry and related methods. The goal is to see how caffeine and alcohol differentially affect ocular and autonomic nervous system activity and whether those effects can serve as noninvasive indicators of recent consumption. The study uses a portable eye device to collect noninvasive measurements during each session. Safety monitoring and standardized procedures are implemented to compare the three conditions across participants.

Why it matters

Who can join: the full rules

Participants must meet the inclusion criteria, as shown below, to participate in this study

Inclusion Criteria

1. Age: 30 to 50 years of age
2. Visual Acuity: Best Corrected Visual Acuity (BCVA) of 0.20 LogMAR or better in both eyes
3. Ability to provide informed consent: Participants must be able to understand and sign the informed consent form
4. Ability to consume both caffeine and alcohol: Participants must be willing and able to consume caffeine and alcohol as part of the study

Participants meeting any of the exclusion criteria, as shown in the table below, will be excluded from participation.

Exclusion Criteria

1. 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.
2. Diagnosed and unresolved neurological conditions:Stroke, unresolved traumatic brain injury, space-occupying lesions in the brain, neuropathies, demyelinating conditions, nerve palsies, etc.
3. Diagnosed systemic conditions that may restrict the participant from drinking caffeine or alcohol: Hypertension, cardiovascular disease, liver disease, kidney disease, etc.
4. Medications: Participants taking any medications that may interact with caffeine or alcohol, affect alertness, or cause drowsiness
5. Previous complex intraocular eye surgery: Participants who have undergone any eye surgery other than uncomplicated refractive surgery.
6. Pregnancy or breastfeeding: Pregnant or breastfeeding women will be excluded from the study, as caffeine and alcohol can affect the fetus or baby
7. History of substance abuse: Participants with a history of substance abuse
8. Allergies or sensitivities: Participants with allergies or sensitivities to caffeine or alcohol
9. 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
10. 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

11- 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

Note: Participants will complete a history update questionnaire at each laboratory visit to report any changes relevant to the exclusion criteria. If a participant no longer meets the eligibility criteria at any visit after the baseline assessment, the visit will either be rescheduled, if appropriate, or the participant will be withdrawn from the study. Reimbursement will be provided on a prorated basis.

\*CCQ: Caffeine Consumption Questionnaire

\*\*AUDIT-C: Alcohol Use Disorders Identification Test-C

Where it's running

• National University of Singapore, E7 Building, Level 7, 15 Kent Ridge Cres
  Singapore, Singapore Recruiting

Study contacts

• Principal investigator: Raymond P. Najjar, PhD — Department of Ophthalmology, National University of Singapore (NUS)
• Study coordinator: Vicknaswari T, Bsc Optometry
• Email: tv96@nus.edu.sg
• Phone: +6565165459

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How to take part

1. Review the eligibility criteria above with your treating physician.
2. Check the official listing on ClinicalTrials.gov for the latest contact details and recruitment status.
3. Contact the study coordinator or principal investigator to ask for pre-screening. Pre-screening is free and never obligates you to enroll.