The goal of this study is to understand how caffeine and alcohol affect the ocular and physiological systems, especially how the pupil (the aperture in the colored part of the eye) responds to light. It will also test whether these changes can be used to detect recent caffeine or alcohol intake using a portable eye device. The main questions it aims to answer are: 1. How does caffeine change pupil responses, eye movements, and other ocular and physiological measurements? 2. How does alcohol change these same ocular and physiological responses? 3. Are the effects of caffeine and alcohol different from each other? 4. Can these changes be used to accurately identify whether someone has consumed caffeine or alcohol? Researchers will compare caffeine, alcohol, and a placebo (a look-alike drink with no active substance) to see how each affects the ocular and physiological outcomes. Participants will: 1. Attend three separate sessions where they will consume caffeine, alcohol, or a placebo (in random order) 2. Undergo pupillary response evaluation using a handheld device that measures responses to different colored light stimuli 3. Have their eye movements analyzed 4. Have retinal and choroidal thickness, blood perfusion, and ocular oxygen levels measured 5. Have basic body measurements recorded (such as pulse rate and blood pressure) 6. Complete tests at multiple time points over 2 hours after consumption The results of this study may help develop a quick and non-invasive way to detect recent caffeine or alcohol use for clinical and safety purposes.
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: 1. Caffeine condition (\~3 mg/kg) 2. Alcohol condition (target blood alcohol concentration \~0.05%) 3. 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: 1. Placebo condition: placebo tablet with a non-alcoholic beverage 2. Alcohol condition: placebo tablet with an alcohol-containing beverage 3. 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. 1. 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. 2. 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. 3. 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. 4. Breath Alcohol Measurement: Breath alcohol concentration will be measured using a breathalyzer at all time points to monitor alcohol levels. 5. 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 Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
DIAGNOSTIC
Masking
TRIPLE
Enrollment
100
Participants receive a matched placebo tablet together with a non-alcoholic beverage identical in appearance and volume to the active conditions. A cornstarch-based formulation may be used for the placebo tablet. Beverage presentation is standardized to maintain blinding across study conditions. No active caffeine or alcohol is administered.
Participants receive a single oral dose of caffeine (\~3 mg/kg body weight) administered in tablet form. The caffeine is given with a non-alcoholic beverage matched to study conditions. All procedures are performed under randomized, double-masked crossover design conditions.
Participants consume a standardized alcoholic beverage designed to achieve a target blood alcohol concentration of approximately 0.05%. A placebo tablet is administered alongside the beverage to maintain masking. All procedures are performed under randomized, double-masked crossover design conditions.
National University of Singapore, E7 Building, Level 7, 15 Kent Ridge Cres
Singapore, Singapore
RECRUITINGBaseline 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.
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
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.
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
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.
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
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.
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
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.
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
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.
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
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.
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
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.
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
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.
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
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.
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
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.
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
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.
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
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.
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 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.
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
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.
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
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.
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
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.
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)
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.
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)
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.
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)
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.
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)
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.
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)
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.
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)
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.
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)
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.
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)
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.
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
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.
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
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.
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
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.
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)
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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 (%).
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
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).
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
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 (%).
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
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).
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
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).
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
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 (°).
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
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.
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
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).
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
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 (%).
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
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).
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
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 (°).
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
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).
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
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 (°).
Time frame: Baseline (pre-intervention), 60 and 120 minutes post-intervention - during each of the 3 study visits (up to 3 study days total)