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| Name | Class |
|---|---|
| Home Team Science & Technology Agency (HTX) | UNKNOWN |
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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:
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:
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.
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:
Study Visit Procedures
At each visit, participants will receive one tablet and one beverage according to 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.
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.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Placebo | Placebo Comparator | Participants receive placebo tablets and non-active beverage under double-masked crossover conditions. |
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| Caffeine | Experimental | Participants receive caffeine administration under double-masked crossover conditions. |
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| Alcohol | Experimental | Participants receive alcohol administration under double-masked crossover conditions. |
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| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| Placebo Comparator: Placebo | Other | 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. |
| Measure | Description | Time Frame |
|---|---|---|
| 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. | 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. | 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. | 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. | 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 |
| Measure | Description | Time Frame |
|---|---|---|
| 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. | Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total) |
| Measure | Description | Time Frame |
|---|---|---|
| Breath Alcohol Concentration | Breath alcohol concentration (BrAC) will be measured using a handheld breathalyzer. BrAC refers to the ethanol concentration in exhaled breath, converted to estimated blood alcohol concentration (BAC) using a standard 1:2100 partition ratio. A target BAC of 0.04-0.06% corresponds to an approximate BrAC of 0.04-0.06 mg/210L. It is measured in mg/210L. | Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total) |
Participants must meet the inclusion criteria, as shown below, to participate in this study
Inclusion Criteria
Participants meeting any of the exclusion criteria, as shown in the table below, will be excluded from participation.
Exclusion Criteria
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
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| Name | Role | Phone | Extension | |
|---|---|---|---|---|
| Vicknaswari T, Bsc Optometry | Contact | +6565165459 | tv96@nus.edu.sg | |
| Najiya S.K Meethal, PhD | Contact | +6591183642 | najiyaskmeethal@nus.edu.sg |
| Name | Affiliation | Role |
|---|---|---|
| Raymond P. Najjar, PhD | Department of Ophthalmology, National University of Singapore (NUS) | Principal Investigator |
| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| National University of Singapore, E7 Building, Level 7, 15 Kent Ridge Cres | Recruiting | Singapore | 119276 | Singapore |
| PubMed Identifier | Type | Citation | Retractions |
|---|---|---|---|
| 29023550 | Background | 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. | |
| 27437402 | Background | Bardak 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. |
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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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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.
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Masking is maintained through separation of study roles. The study team member responsible for preparing the intervention (caffeine, alcohol, or placebo) is not involved in participant assessments or data collection. Outcome assessors and investigators performing pupillometry, imaging, and physiological measurements remain blinded to the assigned condition. Participants are also masked to the intervention received, as all conditions are administered in identical-appearing tablet and beverage forms. The allocation sequence is held by an independent staff member not involved in outcome assessments.
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| Caffeine administration | Other | 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. |
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| 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. |
|
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. |
| 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | 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. | Baseline (pre-intervention), 30, 60, 90, 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. | 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. | 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. | 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 (%). | 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). | 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 (%). | 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). | 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). | 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 (°). | 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. | 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). | 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 (%). | 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). | 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 (°). | 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). | 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 (°). | Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total) |
| Peripheral Oxygen Saturation (SpO₂) | Peripheral oxygen saturation (SpO₂) will be measured using a pulse oximeter. SpO₂ refers to the estimated percentage of oxyhaemoglobin relative to total haemoglobin in peripheral blood, providing a non-invasive measure of systemic oxygenation. It is measured as a percentage (%). | Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total) |
| Pulse Rate | Pulse rate will be measured using automated sphygmomanometry. Pulse rate refers to the number of arterial pulsations per minute, reflecting heart rate and cardiovascular autonomic response to intervention. It is measured in beats per minute (bpm). | Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total) |
| Systolic Blood Pressure | Systolic blood pressure will be measured using automated sphygmomanometry. Systolic blood pressure refers to the peak arterial pressure during cardiac contraction, reflecting cardiovascular autonomic response to intervention. It is measured in millimetres of mercury (mmHg). | Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total) |
| Diastolic Blood Pressure | Diastolic blood pressure will be measured using automated sphygmomanometry. Diastolic blood pressure refers to the minimum arterial pressure during cardiac relaxation, reflecting cardiovascular autonomic response to intervention. It is measured in millimetres of mercury (mmHg). | Baseline (pre-intervention), 30, 60, 90, and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total) |
| Weight | Weight of participant in kilograms | Baseline (pre-intervention) during each of the 3 study visits (up to 3 study days total) |
| Height | Height of the participant in meters | Baseline (pre-intervention) during each of the 3 study visits (up to 3 study days total) |
| Body Mass Index (BMI) | Calculated as participant's weight in kilograms divided by the square of participant's height in meters (kg/m^2). | Calculated at baseline (pre-intervention) during each of the 3 study visits (up to 3 study days total) |
| 24325436 | Background | Wilhelm 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. |
| 32011181 | Background | Redondo 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. |
| 27983733 | Background | Abokyi 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. |
| 30809186 | Background | Rukmini 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. |
| ID | Term |
|---|---|
| D000431 | Ethanol |
| ID | Term |
|---|---|
| D000438 | Alcohols |
| D009930 | Organic Chemicals |
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