CaffeinePACNCT07625358
Investigating the Effect of Caffeine and Alcohol on Pupil Dynamics
A study testing Caffeine administration and Alcohol (Ethanol) in people with Caffeine and Alcohol, run by National University of Singapore at 1 site in Singapore.
Trial 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. Read more about this study
- Who is it for?
- Ages 30 to 50 yearsHealthy volunteers can take part
- Conditions the study is for
- Caffeine, Alcohol, Pupillary Response
- What is being tested?
- Caffeine administration and Alcohol (Ethanol)
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 100 participants
- Where
- 1 siteSingapore
- Study dates
- 1 Jun 2026to 5 Nov 2027
- Phase
- Interventional
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 30 to 50 years
- All sexes
- Healthy volunteers accepted
- Adult
Who may be able to join
- 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
- Participants meeting any of the exclusion criteria, as shown in the table below, will be excluded from participation.
Who cannot join
- 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
Show all 16Show fewer
- 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
- 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
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
Singapore1 site, 1 recruiting
- Recruiting
National University of Singapore, E7 Building, Level 7, 15 Kent Ridge Cres
Singapore, 119276
Vicknaswari T, BSc, +6565165459, tv96@nus.edu.sg
Najiya S.K. Meethal, PhD, +6591183642, najiyaskmeethal@nus.edu.sg
About this study
Official title: Investigating the Effect of Caffeine and Alcohol on Pupil Dynamics (PAC)
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:
Read more
- How does caffeine change pupil responses, eye movements, and other ocular and physiological measurements?
- How does alcohol change these same ocular and physiological responses?
- Are the effects of caffeine and alcohol different from each other?
- 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:
- Attend three separate sessions where they will consume caffeine, alcohol, or a placebo (in random order)
- Undergo pupillary response evaluation using a handheld device that measures responses to different colored light stimuli
- Have their eye movements analyzed
- Have retinal and choroidal thickness, blood perfusion, and ocular oxygen levels measured
- Have basic body measurements recorded (such as pulse rate and blood pressure)
- 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.
Read the detailed description
Caffeine and alcohol are widely consumed psychoactive substances that affect the central and autonomic nervous systems. These effects can influence ocular function, including pupil responses to light, eye movements, and retinal physiology. However, objective and non-invasive methods to detect and differentiate these effects remain limited.
The pupillary light reflex is a sensitive indicator of autonomic nervous system activity. Chromatic pupillometry, which uses different colored light stimuli, allows assessment of specific retinal pathways and provides detailed information about pupil function. This study aims to determine whether changes in pupillary responses and other ocular measurements can be used to detect recent caffeine or alcohol consumption.
Study Design and Procedures A total of 100 healthy adults aged 30-50 years will participate in this study.
Each participant will attend three study visits, corresponding to the following conditions:
- Caffeine condition (~3 mg/kg)
- Alcohol condition (target blood alcohol concentration ~0.05%)
- Placebo condition The order of conditions will be randomized. This is a double-masked, within-subject crossover study, where each participant undergoes all three conditions.
Study Visit Procedures
At each visit, participants will receive one tablet and one beverage according to the assigned condition:
- Placebo condition: placebo tablet with a non-alcoholic beverage
- Alcohol condition: placebo tablet with an alcohol-containing beverage
- Caffeine condition: caffeine tablet with a non-alcoholic beverage Procedures will be standardized to maintain masking, and study personnel performing assessments will remain unaware of the assigned condition.
Assessments All measurements will be performed at baseline (before consumption) and at 30, 60, 90, and 120 minutes after consumption, unless otherwise specified.
- Pupillary Assessment: Pupillary responses will be measured using a handheld chromatic pupillometry device in a controlled dark environment. Different colored light stimuli will be used to assess pupil function.
- Eye Movement Analysis: Eye movements will be recorded to evaluate oculomotor function, including tracking, fixation, and gaze behavior at baseline, 60 minutes, and 120 minutes.
- Retinal and Choroidal Imaging: Retinal and choroidal thickness and blood perfusion will be measured using optical coherence tomography (OCT) and OCT angiography at baseline, 60 minutes, and 120 minutes.
- Breath Alcohol Measurement: Breath alcohol concentration will be measured using a breathalyzer at all time points to monitor alcohol levels.
- Physiological Measurements: Basic physiological parameters will be recorded, including: Pulse rate, Blood pressure, Blood Oxygen saturation
Data Analysis Data from pupillary responses, eye movements, retinal imaging, and physiological measurements will be combined to identify patterns associated with caffeine and alcohol intake.
Expected Outcomes This study aims to identify measurable changes in pupil responses and other ocular parameters following caffeine and alcohol consumption. It will also evaluate whether a portable, non-invasive system can be used to detect alcohol and caffeine consumption.
The findings may support the development of rapid and objective screening tools for clinical, occupational, and public safety applications.
- Conditions
- Caffeine, Alcohol, Pupillary Response, Eye Movements, Optical Coherence Tomography, Optical Coherence Tomography Angiography
- Being tested
- Placebo Comparator: Placebo, Caffeine administration, Alcohol (Ethanol)
- Keywords
- Caffeine, Alcohol, Pupillary light reflex, Pupillometry, Chromatic pupillometry, Eye movements, Oculomotor function, Optical coherence tomography, Optical coherence tomography angiography, Physiological responses, Machine learning, Non-invasive monitoring
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Placebo Comparator: PlaceboOther
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.
Caffeine administrationOther
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.
Alcohol (Ethanol)Other
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.
| Study group | Role | What they receive |
|---|---|---|
| Placebo | Placebo comparator | Participants receive placebo tablets and non-active beverage under double-masked crossover conditions. Receives: Other: Placebo Comparator: Placebo |
| Caffeine | Experimental | Participants receive caffeine administration under double-masked crossover conditions. Receives: Other: Caffeine administration |
| Alcohol | Experimental | Participants receive alcohol administration under double-masked crossover conditions. Receives: Other: Alcohol (Ethanol) |
What is being measured
The primary outcome is the main question the study is designed to answer.
Baseline Pupil Size
Baseline pupil size will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Baseline pupil size refers to the resting pupil diameter measured prior to light stimulation. It is measured in pixels.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Phasic Pupil Constriction to Blue Light
Phasic pupil constriction to blue light will be quantified using handheld chromatic pupillometry. Phasic pupil constriction to blue light refers to the rapid, transient decrease in pupil diameter that occurs immediately after the onset of a blue light stimulus. It is calculated as a percentage change from baseline.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Maximum Pupil Constriction to Blue Light
Maximum pupil constriction to blue light will be quantified using handheld chromatic pupillometry. Maximum pupil constriction to blue light refers to the greatest reduction in pupil diameter observed following the onset of a blue light stimulus. It is calculated as a percentage change from baseline.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Pupil Constriction Latency to Blue Light
Pupil constriction latency to blue light will be quantified using handheld chromatic pupillometry. Constriction latency is defined as the time from blue light onset to the first detectable decrease in pupil diameter relative to baseline. It is measured in seconds or milliseconds.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Phasic Pupil Constriction to Red Light
Phasic pupil constriction to red light will be quantified using handheld chromatic pupillometry. Phasic pupil constriction to red light refers to the rapid, transient decrease in pupil diameter that occurs immediately after the onset of a red light stimulus. It is calculated as a percentage change from baseline.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Maximum Pupil Constriction to Red Light
Maximum pupil constriction to red light will be quantified using handheld chromatic pupillometry. Maximum pupil constriction to red light refers to the greatest reduction in pupil diameter observed following the onset of a red light stimulus. It is calculated as a percentage change from baseline.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Pupil Constriction Latency to Red Light
Pupil constriction latency to red light will be quantified using handheld chromatic pupillometry. Constriction latency is defined as the time from red light onset to the first detectable decrease in pupil diameter relative to baseline. It is measured in seconds or milliseconds.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Phasic Pupil Constriction to Continuous White Light
Phasic pupil constriction to continuous white light will be quantified using handheld chromatic pupillometry. Phasic pupil constriction to white light refers to the rapid, transient decrease in pupil diameter that occurs immediately after the onset of a white light stimulus. It is calculated as a percentage change from baseline.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Maximum Pupil Constriction to Continuous White Light
Maximum pupil constriction to continuous white light will be quantified using handheld chromatic pupillometry. Maximum pupil constriction to white light refers to the greatest reduction in pupil diameter observed following the onset of a white light stimulus. It is calculated as a percentage change from baseline.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Pupil Constriction Latency to Continuous White Light
Pupil constriction latency to continuous white light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Constriction latency is defined as the time from white light onset to the first detectable decrease in pupil diameter relative to baseline. It is measured in seconds.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Maximum Pupil Constriction to White Light Flash
Maximum pupil constriction to white light flash will be quantified using using handheld chromatic pupillometry. Maximum pupil constriction to white light refers to the greatest reduction in pupil diameter observed following the onset of a white light stimulus. It is calculated as a percentage change from baseline.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-Stimulus Pupil Recovery Slope to Blue Light
Post-stimulus pupil recovery slope to blue light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Post-stimulus pupil recovery slope refers to the rate of pupil re-dilation following the offset of a blue light stimulus. It is calculated as percentage change per second.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Pupil Slope to Blue Light 1.7s before Blue Light Offset
Pupil slope to blue light 1.7s before blue light offset will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Pupil slope to blue light within the last 1.7s refers to the rate of pupil re-dilation just before the offset of a blue light stimulus. It is calculated as percentage change per second.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Pupil Slope to Blue Light 1.7s after Blue Light Offset
Pupil slope to blue light in the 1.7s after blue light offset will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Pupil slope to blue light in the 1.7s after blue light offset refers to the rate of pupil re-dilation just after the offset of a blue light stimulus. It is calculated as percentage change per second.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-Stimulus Pupil Recovery Slope to Red Light
Post-stimulus pupil recovery slope to red light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Post-stimulus pupil recovery slope refers to the rate of pupil re-dilation following the offset of a red light stimulus. It is calculated as percentage change per second.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-Stimulus Pupil Recovery Slope to White Light Flash
Post-stimulus pupil recovery slope to white light flash will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Post-stimulus pupil recovery slope refers to the rate of pupil re-dilation following the offset of a white light stimulus. It is calculated as percentage change per second.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-Stimulus Pupil Recovery Slope to Continuous White Light
Post-stimulus pupil recovery slope to continuous white light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Post-stimulus pupil recovery slope refers to the rate of pupil re-dilation following the offset of a white light stimulus. It is calculated as percentage change per second.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
PIPR at 6 s - Blue Light
Post-illumination pupillary responses (PIPR) to blue light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR at 6 s is measured as pupil size at 6 seconds after blue light offset. It is calculated as a percentage of baseline pupil size.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
PIPR at 12 s - Blue Light
Post-illumination pupillary responses (PIPR) to blue light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR at 12 s is measured as pupil size at 12 seconds after blue light offset. It is calculated as a percentage of baseline pupil size.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
PIPR Area Under the Curve (0-12 s) - Blue Light
Post-illumination pupillary responses (PIPR) to blue light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR area under the curve (AUC) from 0 to 12 seconds captures the total magnitude and duration of the sustained post-illumination response. It is calculated as the integrated area in %.s.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
PIPR at 6 s - Red Light
Post-illumination pupillary responses (PIPR) to red light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR at 6 s is measured as pupil size at 6 seconds after red light offset. It is calculated as a percentage of baseline pupil size.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
PIPR Area Under the Curve - Red Light
Post-illumination pupillary responses (PIPR) to red light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR area under the curve (AUC) from 0 to end of recording captures the total magnitude and duration of the sustained post-illumination response. It is calculated as the integrated area in %.s.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
PIPR at 6 s - Flash White Light
Post-illumination pupillary responses (PIPR) to white light flash will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR at 6 s is measured as pupil size at 6 seconds after white light offset. It is calculated as a percentage of baseline pupil size.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
PIPR at 6 s - Continuous White Light
Post-illumination pupillary responses (PIPR) to continuous white light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR at 6 s is measured as pupil size at 6 seconds after white light offset. It is calculated as a percentage of baseline pupil size.
Measured: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Secondary outcomes (17)
Retinal Thickness
Retinal thickness will be assessed using Triton swept-source optical coherence tomography (SS-OCT). Retinal thickness is defined as the axial distance between the internal limiting membrane and the retinal pigment epithelium, measured in micrometres (µm), and is automatically quantified across the nine ETDRS subfields of the 12 × 9 mm macular volume scan.
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Choroidal Thickness
Choroidal thickness will be assessed using swept-source optical coherence tomography (SS-OCT). Choroidal thickness is defined as the perpendicular distance between the outer boundary of Bruch's membrane and the chorioscleral interface, measured in micrometres (µm), and is automatically segmented across the nine ETDRS subfields.
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Superficial Capillary Plexus Vessel Density
Vessel density of the superficial capillary plexus (SCP) will be assessed using optical coherence tomography angiography (OCTA). Using the 6 × 6 mm macular OCTA scan, the SCP is automatically segmented by the built-in IMAGEnet software. Vessel density is defined as the proportion of the measurement area occupied by detected blood flow signals, reported as a percentage (%) across the whole image and individual ETDRS subfields.
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Deep Capillary Plexus Vessel Density
Vessel density of the deep capillary plexus (DCP) will be assessed using optical coherence tomography angiography (OCTA). Using the 6 × 6 mm macular OCTA scan, the DCP is automatically segmented by the built-in IMAGEnet software. Vessel density is defined as the proportion of the measurement area occupied by detected blood flow signals, reported as a percentage (%) across the whole image and individual ETDRS subfields.
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Choriocapillaris Vessel Density
Choriocapillaris vessel density will be assessed using optical coherence tomography angiography (OCTA). Using the 6 × 6 mm macular OCTA scan, the choriocapillaris slab is automatically segmented from 0 to 10.4 µm below the outer boundary of Bruch's membrane. Vessel density is defined as the proportion of the measurement area exhibiting detectable flow signal relative to the total sampled area, reported as a percentage (%).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Foveal Avascular Zone Area
Foveal avascular zone (FAZ) area will be assessed using optical coherence tomography angiography (OCTA). Using the 6 × 6 mm macular OCTA scan, the FAZ is automatically delineated at the level of the superficial capillary plexus by the built-in IMAGEnet software. FAZ area is defined as the area of the capillary-free region centred on the fovea, measured in square millimetres (mm²).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Choroidal Vascularity Index
The choroidal vascularity index (CVI) will be derived from the subfoveal horizontal B-scan of the 12 × 9 mm SS-OCT macular scan. The segmented choroidal region, bounded by Bruch's membrane and the chorioscleral interface, is binarised into luminal (vascular) and stromal areas. CVI is calculated as the ratio of luminal choroidal area to total choroidal area, expressed as a percentage (%).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Prosaccade Latency
Prosaccade latency will be assessed using eye tracking. Prosaccade latency refers to the time interval between the onset of a visual target and the initiation of the corresponding prosaccade eye movement. It is measured in milliseconds (ms).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Prosaccade Peak Velocity
Prosaccade peak velocity will be assessed using eye tracking. Prosaccade peak velocity refers to the maximum angular velocity achieved during a prosaccade movement. It is measured in degrees per second (°/s).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Prosaccade Amplitude
Prosaccade amplitude will be assessed using eye tracking. Prosaccade amplitude refers to the total angular displacement of the eye during a prosaccade movement. It is measured in degrees (°).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Smooth Pursuit Gain
Smooth pursuit gain will be assessed using eye tracking. Smooth pursuit gain refers to the ratio of eye velocity to target velocity during smooth pursuit tracking, where a value of 1.0 indicates perfect tracking. It is expressed as a unitless ratio.
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Catch-Up Saccade Frequency During Smooth Pursuit
Catch-up saccade frequency will be assessed using eye tracking. Catch-up saccade frequency refers to the number of corrective saccades per second that occur during smooth pursuit tracking, reflecting the degree of pursuit impairment. It is measured as events per second (events/s).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Smooth Pursuit Tracking Accuracy
Smooth pursuit tracking accuracy will be assessed using eye tracking. Smooth pursuit tracking accuracy refers to the proportion of time the eye position is within an acceptable error window of the pursuit target trajectory. It is calculated as a percentage (%).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Micro-Saccade Rate During Fixation
Micro-saccade rate will be assessed using eye tracking during a sustained fixation task (30-60 s). Micro-saccade rate refers to the number of micro-saccade events per second during sustained fixation, reflecting fixation stability and cortical arousal. It is measured as events per second (events/s).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Fixation Dispersion
Fixation dispersion will be assessed using eye tracking during a sustained fixation task (30-60 s). Fixation dispersion refers to the angular spread of gaze position around the fixation target during sustained fixation, quantifying the spatial extent of fixation instability. It is measured in degrees (°).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Fixation Duration During Free Viewing
Fixation duration during free viewing will be assessed using eye tracking. Fixation duration refers to the mean duration of individual fixations during free viewing of a standardised stimulus, reflecting attentional dwell time. It is measured in milliseconds (ms).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Scanpath Variability During Free Viewing
Scanpath variability during free viewing will be assessed using eye tracking. Scanpath variability refers to the angular variability of the gaze trajectory during free viewing, characterising the spread and consistency of spontaneous viewing patterns. It is measured in degrees (°).
Measured: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted4 Jun 2026
- Study start1 Jun 2026 (estimated)
- Primary completion5 May 2027 (estimated)
- Study completion5 Nov 2027 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (6)Papers the sponsor has linked to this study.
- Other trials for CaffeineStudies of the same condition, open and under way.
- More trials run by National University of SingaporeThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Diagnosis
- Allocation
- Randomised
- Intervention model
- Crossover
- Model description
- In this study, the cross-over model refers to the way each participant experiences all three experimental conditions: caffeine, alcohol, and placebo. Each participant completes three separate study visits, with one condition administered per visit. The order of conditions is randomized. Some participants will start with caffeine, followed by alcohol and a placebo, while others will receive a different sequence. This randomization helps prevent order effects, such as changes in physiological responses due to learning, adaptation, or fatigue across repeated sessions on the observed results. Because each participant receives all three conditions, they act as their own control, allowing direct comparison of ocular and physiological responses across caffeine, alcohol, and placebo conditions.
- Masking
- Triple blind
- Who is masked
- Participant, Investigator, Outcomes assessor
- Enrolment
- 100 participants (estimated)
Sponsor and investigators
- Lead sponsor
- National University of Singapore
- Sponsor type
- University, hospital or other
- Collaborators
- Home Team Science & Technology Agency (HTX)
- Responsible party
- Principal investigator, Raymond P. Najjar, PhD, National University of Singapore
- Investigators
- Raymond P. Najjar, PhD, Principal investigator, Department of Ophthalmology, National University of Singapore (NUS)
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07625358
- Sponsor's protocol ID
- NUS-IRB-2025-1150
- Acronym
- PAC
- Status last verified
- May 2026
- First submitted
- 18 May 2026
- Last updated
- 4 Jun 2026
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Undecided: Individual participant data (IPD) may not be shared due to participant confidentiality, privacy protection, and compliance with institutional or sponsor and regulatory data governance policies.
Publications
Silva JBS, Cristino ED, Almeida NL, Medeiros PCB, Santos NAD. Effects of acute alcohol ingestion on eye movements and cognition: A double-blind, placebo-controlled study. PLoS One. 2017 Oct 12;12(10):e0186061. doi: 10.1371/journal.pone.0186061. eCollection 2017.
PubMed 29023550Bardak H, Gunay M, Mumcu U, Bardak Y. Effect of Single Administration of Coffee on Pupil Size and Ocular Wavefront Aberration Measurements in Healthy Subjects. Biomed Res Int. 2016;2016:9578308. doi: 10.1155/2016/9578308. Epub 2016 Jun 29.
PubMed 27437402Wilhelm B, Stuiber G, Ludtke H, Wilhelm H. The effect of caffeine on spontaneous pupillary oscillations. Ophthalmic Physiol Opt. 2014 Jan;34(1):73-81. doi: 10.1111/opo.12094.
PubMed 24325436Redondo B, Vera J, Carreno-Rodriguez C, Molina-Romero R, Jimenez R. Acute Effects of Caffeine on Dynamic Accommodative Response and Pupil Size: A Placebo-controlled, Double-blind, Balanced Crossover Study. Curr Eye Res. 2020 Sep;45(9):1074-1081. doi: 10.1080/02713683.2020.1725060. Epub 2020 Feb 11.
PubMed 32011181Abokyi S, Owusu-Mensah J, Osei KA. Caffeine intake is associated with pupil dilation and enhanced accommodation. Eye (Lond). 2017 Apr;31(4):615-619. doi: 10.1038/eye.2016.288. Epub 2016 Dec 16.
PubMed 27983733Rukmini AV, Milea D, Gooley JJ. Chromatic Pupillometry Methods for Assessing Photoreceptor Health in Retinal and Optic Nerve Diseases. Front Neurol. 2019 Feb 12;10:76. doi: 10.3389/fneur.2019.00076. eCollection 2019.
PubMed 30809186
Study at a glance
From the registry record, last updated by the sponsor on 4 Jun 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Investigating the Effect of Caffeine and Alcohol on Pupil Dynamics (PAC)
- ClinicalTrials.gov ID
- NCT07625358
- Acronym / sponsor ID
- PAC / NUS-IRB-2025-1150
- Conditions
- Caffeine, Alcohol, Pupillary Response, Eye Movements, Optical Coherence Tomography, Optical Coherence Tomography Angiography
- Keywords
- Caffeine, Alcohol, Pupillary light reflex, Pupillometry, Chromatic pupillometry, Eye movements, Oculomotor function, Optical coherence tomography
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 100 participants (estimated)
- Lead sponsor
- National University of SingaporeUniversity, hospital or other
- Collaborators
- Home Team Science & Technology Agency (HTX)
- Study start
- 1 Jun 2026 (estimated)
- Primary completion
- 5 May 2027 (estimated)
- Study completion
- 5 Nov 2027 (estimated)
- First posted
- 4 Jun 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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:
- How does caffeine change pupil responses, eye movements, and other ocular and physiological measurements?
- How does alcohol change these same ocular and physiological responses?
- Are the effects of caffeine and alcohol different from each other?
- 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:
- Attend three separate sessions where they will consume caffeine, alcohol, or a placebo (in random order)
- Undergo pupillary response evaluation using a handheld device that measures responses to different colored light stimuli
- Have their eye movements analyzed
- Have retinal and choroidal thickness, blood perfusion, and ocular oxygen levels measured
- Have basic body measurements recorded (such as pulse rate and blood pressure)
- 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.
Detailed description
Caffeine and alcohol are widely consumed psychoactive substances that affect the central and autonomic nervous systems. These effects can influence ocular function, including pupil responses to light, eye movements, and retinal physiology. However, objective and non-invasive methods to detect and differentiate these effects remain limited.
The pupillary light reflex is a sensitive indicator of autonomic nervous system activity. Chromatic pupillometry, which uses different colored light stimuli, allows assessment of specific retinal pathways and provides detailed information about pupil function. This study aims to determine whether changes in pupillary responses and other ocular measurements can be used to detect recent caffeine or alcohol consumption.
Study Design and Procedures A total of 100 healthy adults aged 30-50 years will participate in this study.
Each participant will attend three study visits, corresponding to the following conditions:
- Caffeine condition (~3 mg/kg)
- Alcohol condition (target blood alcohol concentration ~0.05%)
- Placebo condition The order of conditions will be randomized. This is a double-masked, within-subject crossover study, where each participant undergoes all three conditions.
Study Visit Procedures
At each visit, participants will receive one tablet and one beverage according to the assigned condition:
- Placebo condition: placebo tablet with a non-alcoholic beverage
- Alcohol condition: placebo tablet with an alcohol-containing beverage
- Caffeine condition: caffeine tablet with a non-alcoholic beverage Procedures will be standardized to maintain masking, and study personnel performing assessments will remain unaware of the assigned condition.
Assessments All measurements will be performed at baseline (before consumption) and at 30, 60, 90, and 120 minutes after consumption, unless otherwise specified.
- Pupillary Assessment: Pupillary responses will be measured using a handheld chromatic pupillometry device in a controlled dark environment. Different colored light stimuli will be used to assess pupil function.
- Eye Movement Analysis: Eye movements will be recorded to evaluate oculomotor function, including tracking, fixation, and gaze behavior at baseline, 60 minutes, and 120 minutes.
- Retinal and Choroidal Imaging: Retinal and choroidal thickness and blood perfusion will be measured using optical coherence tomography (OCT) and OCT angiography at baseline, 60 minutes, and 120 minutes.
- Breath Alcohol Measurement: Breath alcohol concentration will be measured using a breathalyzer at all time points to monitor alcohol levels.
- Physiological Measurements: Basic physiological parameters will be recorded, including: Pulse rate, Blood pressure, Blood Oxygen saturation
Data Analysis Data from pupillary responses, eye movements, retinal imaging, and physiological measurements will be combined to identify patterns associated with caffeine and alcohol intake.
Expected Outcomes This study aims to identify measurable changes in pupil responses and other ocular parameters following caffeine and alcohol consumption. It will also evaluate whether a portable, non-invasive system can be used to detect alcohol and caffeine consumption.
The findings may support the development of rapid and objective screening tools for clinical, occupational, and public safety applications.
Study design
- Primary purpose
- Diagnosis
- Allocation
- Randomised
- Intervention model
- Crossover
- Masking
- Triple blind (participant, investigator, outcomes assessor)
- Number of arms
- 3
- Model description
- In this study, the cross-over model refers to the way each participant experiences all three experimental conditions: caffeine, alcohol, and placebo. Each participant completes three separate study visits, with one condition administered per visit. The order of conditions is randomized. Some participants will start with caffeine, followed by alcohol and a placebo, while others will receive a different sequence. This randomization helps prevent order effects, such as changes in physiological responses due to learning, adaptation, or fatigue across repeated sessions on the observed results. Because each participant receives all three conditions, they act as their own control, allowing direct comparison of ocular and physiological responses across caffeine, alcohol, and placebo conditions.
| Arm | Type | Receives |
|---|---|---|
| Placebo | Placebo comparator | Other: Placebo Comparator: PlaceboParticipants receive placebo tablets and non-active beverage under double-masked crossover conditions. |
| Caffeine | Experimental | Other: Caffeine administrationParticipants receive caffeine administration under double-masked crossover conditions. |
| Alcohol | Experimental | Other: Alcohol (Ethanol)Participants receive alcohol administration under double-masked crossover conditions. |
Who may qualify
- Ages
- 30 to 50 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (5 listed)
- 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
- Participants meeting any of the exclusion criteria, as shown in the table below, will be excluded from participation.
Key exclusion criteria (16 listed)
- 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.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Placebo Comparator: PlaceboParticipants 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. | Other | Placebo |
| Caffeine administrationParticipants 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. | Other | Caffeine |
| Alcohol (Ethanol)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. | Other | Alcohol |
Primary outcome
Baseline Pupil Size
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Baseline pupil size will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Baseline pupil size refers to the resting pupil diameter measured prior to light stimulation. It is measured in pixels.
Phasic Pupil Constriction to Blue Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Phasic pupil constriction to blue light will be quantified using handheld chromatic pupillometry. Phasic pupil constriction to blue light refers to the rapid, transient decrease in pupil diameter that occurs immediately after the onset of a blue light stimulus. It is calculated as a percentage change from baseline.
Maximum Pupil Constriction to Blue Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Maximum pupil constriction to blue light will be quantified using handheld chromatic pupillometry. Maximum pupil constriction to blue light refers to the greatest reduction in pupil diameter observed following the onset of a blue light stimulus. It is calculated as a percentage change from baseline.
Pupil Constriction Latency to Blue Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Pupil constriction latency to blue light will be quantified using handheld chromatic pupillometry. Constriction latency is defined as the time from blue light onset to the first detectable decrease in pupil diameter relative to baseline. It is measured in seconds or milliseconds.
Phasic Pupil Constriction to Red Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Phasic pupil constriction to red light will be quantified using handheld chromatic pupillometry. Phasic pupil constriction to red light refers to the rapid, transient decrease in pupil diameter that occurs immediately after the onset of a red light stimulus. It is calculated as a percentage change from baseline.
Maximum Pupil Constriction to Red Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Maximum pupil constriction to red light will be quantified using handheld chromatic pupillometry. Maximum pupil constriction to red light refers to the greatest reduction in pupil diameter observed following the onset of a red light stimulus. It is calculated as a percentage change from baseline.
Pupil Constriction Latency to Red Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Pupil constriction latency to red light will be quantified using handheld chromatic pupillometry. Constriction latency is defined as the time from red light onset to the first detectable decrease in pupil diameter relative to baseline. It is measured in seconds or milliseconds.
Phasic Pupil Constriction to Continuous White Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Phasic pupil constriction to continuous white light will be quantified using handheld chromatic pupillometry. Phasic pupil constriction to white light refers to the rapid, transient decrease in pupil diameter that occurs immediately after the onset of a white light stimulus. It is calculated as a percentage change from baseline.
Maximum Pupil Constriction to Continuous White Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Maximum pupil constriction to continuous white light will be quantified using handheld chromatic pupillometry. Maximum pupil constriction to white light refers to the greatest reduction in pupil diameter observed following the onset of a white light stimulus. It is calculated as a percentage change from baseline.
Pupil Constriction Latency to Continuous White Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Pupil constriction latency to continuous white light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Constriction latency is defined as the time from white light onset to the first detectable decrease in pupil diameter relative to baseline. It is measured in seconds.
Maximum Pupil Constriction to White Light Flash
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Maximum pupil constriction to white light flash will be quantified using using handheld chromatic pupillometry. Maximum pupil constriction to white light refers to the greatest reduction in pupil diameter observed following the onset of a white light stimulus. It is calculated as a percentage change from baseline.
Post-Stimulus Pupil Recovery Slope to Blue Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-stimulus pupil recovery slope to blue light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Post-stimulus pupil recovery slope refers to the rate of pupil re-dilation following the offset of a blue light stimulus. It is calculated as percentage change per second.
Pupil Slope to Blue Light 1.7s before Blue Light Offset
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Pupil slope to blue light 1.7s before blue light offset will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Pupil slope to blue light within the last 1.7s refers to the rate of pupil re-dilation just before the offset of a blue light stimulus. It is calculated as percentage change per second.
Pupil Slope to Blue Light 1.7s after Blue Light Offset
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Pupil slope to blue light in the 1.7s after blue light offset will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Pupil slope to blue light in the 1.7s after blue light offset refers to the rate of pupil re-dilation just after the offset of a blue light stimulus. It is calculated as percentage change per second.
Post-Stimulus Pupil Recovery Slope to Red Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-stimulus pupil recovery slope to red light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Post-stimulus pupil recovery slope refers to the rate of pupil re-dilation following the offset of a red light stimulus. It is calculated as percentage change per second.
Post-Stimulus Pupil Recovery Slope to White Light Flash
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-stimulus pupil recovery slope to white light flash will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Post-stimulus pupil recovery slope refers to the rate of pupil re-dilation following the offset of a white light stimulus. It is calculated as percentage change per second.
Post-Stimulus Pupil Recovery Slope to Continuous White Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-stimulus pupil recovery slope to continuous white light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. Post-stimulus pupil recovery slope refers to the rate of pupil re-dilation following the offset of a white light stimulus. It is calculated as percentage change per second.
PIPR at 6 s - Blue Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-illumination pupillary responses (PIPR) to blue light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR at 6 s is measured as pupil size at 6 seconds after blue light offset. It is calculated as a percentage of baseline pupil size.
PIPR at 12 s - Blue Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-illumination pupillary responses (PIPR) to blue light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR at 12 s is measured as pupil size at 12 seconds after blue light offset. It is calculated as a percentage of baseline pupil size.
PIPR Area Under the Curve (0-12 s) - Blue Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-illumination pupillary responses (PIPR) to blue light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR area under the curve (AUC) from 0 to 12 seconds captures the total magnitude and duration of the sustained post-illumination response. It is calculated as the integrated area in %.s.
PIPR at 6 s - Red Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-illumination pupillary responses (PIPR) to red light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR at 6 s is measured as pupil size at 6 seconds after red light offset. It is calculated as a percentage of baseline pupil size.
PIPR Area Under the Curve - Red Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-illumination pupillary responses (PIPR) to red light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR area under the curve (AUC) from 0 to end of recording captures the total magnitude and duration of the sustained post-illumination response. It is calculated as the integrated area in %.s.
PIPR at 6 s - Flash White Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-illumination pupillary responses (PIPR) to white light flash will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR at 6 s is measured as pupil size at 6 seconds after white light offset. It is calculated as a percentage of baseline pupil size.
PIPR at 6 s - Continuous White Light
Time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Post-illumination pupillary responses (PIPR) to continuous white light will be quantified using chromatic pupillometry with a handheld chromatic pupillometer. PIPR refers to the sustained pupil constriction that persists after the termination of a light stimulus. PIPR at 6 s is measured as pupil size at 6 seconds after white light offset. It is calculated as a percentage of baseline pupil size.
17 secondary outcomes
Retinal Thickness
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Choroidal Thickness
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Superficial Capillary Plexus Vessel Density
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Deep Capillary Plexus Vessel Density
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Choriocapillaris Vessel Density
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Foveal Avascular Zone Area
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Choroidal Vascularity Index
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Prosaccade Latency
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Prosaccade Peak Velocity
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Prosaccade Amplitude
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Smooth Pursuit Gain
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Catch-Up Saccade Frequency During Smooth Pursuit
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Smooth Pursuit Tracking Accuracy
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Micro-Saccade Rate During Fixation
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Fixation Dispersion
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Fixation Duration During Free Viewing
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Scanpath Variability During Free Viewing
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 4 Jun 2026.
- Background: PubMed 29023550Silva JBS, Cristino ED, Almeida NL, Medeiros PCB, Santos NAD. Effects of acute alcohol ingestion on eye movements and cognition: A double-blind, placebo-controlled study. PLoS One. 2017 Oct 12;12(10):e0186061. doi: 10.1371/journal.pone.0186061. eCollection 2017.
- Background: PubMed 27437402Bardak H, Gunay M, Mumcu U, Bardak Y. Effect of Single Administration of Coffee on Pupil Size and Ocular Wavefront Aberration Measurements in Healthy Subjects. Biomed Res Int. 2016;2016:9578308. doi: 10.1155/2016/9578308. Epub 2016 Jun 29.
- Background: PubMed 24325436Wilhelm B, Stuiber G, Ludtke H, Wilhelm H. The effect of caffeine on spontaneous pupillary oscillations. Ophthalmic Physiol Opt. 2014 Jan;34(1):73-81. doi: 10.1111/opo.12094.
- Background: PubMed 32011181Redondo B, Vera J, Carreno-Rodriguez C, Molina-Romero R, Jimenez R. Acute Effects of Caffeine on Dynamic Accommodative Response and Pupil Size: A Placebo-controlled, Double-blind, Balanced Crossover Study. Curr Eye Res. 2020 Sep;45(9):1074-1081. doi: 10.1080/02713683.2020.1725060. Epub 2020 Feb 11.
- Background: PubMed 27983733Abokyi S, Owusu-Mensah J, Osei KA. Caffeine intake is associated with pupil dilation and enhanced accommodation. Eye (Lond). 2017 Apr;31(4):615-619. doi: 10.1038/eye.2016.288. Epub 2016 Dec 16.
- Background: PubMed 30809186Rukmini AV, Milea D, Gooley JJ. Chromatic Pupillometry Methods for Assessing Photoreceptor Health in Retinal and Optic Nerve Diseases. Front Neurol. 2019 Feb 12;10:76. doi: 10.3389/fneur.2019.00076. eCollection 2019.
- Individual participant dataSharing planned: Undecided. Individual participant data (IPD) may not be shared due to participant confidentiality, privacy protection, and compliance with institutional or sponsor and regulatory data governance policies.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Raymond P. Najjar, PhD principal investigator
Department of Ophthalmology, National University of Singapore (NUS)
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Caffeine administration and Alcohol (Ethanol) in people with Caffeine and Alcohol, run by National University of Singapore at 1 site in Singapore.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 5 inclusion and 16 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 4 Jun 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Singapore. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Vicknaswari T, Bsc Optometry (+6565165459, tv96@nus.edu.sg), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Baseline Pupil Size (time frame: Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)). The study lists 24 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT07625358, which also lists 6 linked publications.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 4 Jun 2026.