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.
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
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
Crossover
Placebo Comparator: Placebo
Other interventionParticipants 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 administration
Other interventionParticipants 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 interventionParticipants 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 (%).
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).
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).
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National University of Singapore
Lead sponsor
Home Team Science & Technology Agency (HTX)
Collaborator
