Investigating the Effect of Caffeine and Alcohol on Pupil Dynamics

Participants must meet the inclusion criteria, as shown below, to participate in this study Inclusion Criteria 1. Age: 30 to 50 years of age 2. Visual Acuity: Best Corrected Visual Acuity (BCVA) of 0.20 LogMAR or better in both eyes 3. Ability to provide informed consent: Participants must be able to understand and sign the informed consent form 4. Ability to consume both caffeine and alcohol: Participants must be willing and able to consume caffeine and alcohol as part of the study Participants meeting any of the exclusion criteria, as shown in the table below, will be excluded from participation. Exclusion Criteria 1. Diagnosed ocular conditions: Participants with ocular or ocular movement diseases such as glaucoma, age-related macular degeneration, diabetic retinopathy, amblyopia, severe ptosis, or conditions relating to pupils: anisocoria, irregular pupil, Adie tonic, Horner's syndrome, Argyll Robertson pupil, etc. These exclude cataracts, refractive errors, and any ocular condition not affecting vision or ocular movement or obstructing the pupil. 2. Diagnosed and unresolved neurological conditions:Stroke, unresolved traumatic brain injury, space-occupying lesions in the brain, neuropathies, demyelinating conditions, nerve palsies, etc. 3. Diagnosed systemic conditions that may restrict the participant from drinking caffeine or alcohol: Hypertension, cardiovascular disease, liver disease, kidney disease, etc. 4. Medications: Participants taking any medications that may interact with caffeine or alcohol, affect alertness, or cause drowsiness 5. Previous complex intraocular eye surgery: Participants who have undergone any eye surgery other than uncomplicated refractive surgery. 6. Pregnancy or breastfeeding: Pregnant or breastfeeding women will be excluded from the study, as caffeine and alcohol can affect the fetus or baby 7. History of substance abuse: Participants with a history of substance abuse 8. Allergies or sensitivities: Participants with allergies or sensitivities to caffeine or alcohol 9. Shift work or having travelled across 2 time zones over the past 2 weeks: This is essential to avoid any impact of sleep deprivation on our outcome measures 10. Non-consumers or light-consumers of caffeine and alcohol Participants who are light consumers of caffeine or alcohol will be excluded due to higher sensitivity to side effects. Caffeine: If less than 100 mg of caffeine per week from all sources (including coffee, soft drinks, energy drinks, chocolate, and medications) based on the CCQ\* Alcohol: If AUDIT-C\*\* score less than 1 11- Extremely frequent consumers Participants who are extremely frequent consumers of caffeine or alcohol will be excluded due to potential withdrawal symptoms during the required 18-hour abstinence and possible reduced sensitivity to administered doses. Caffeine: If more than 400mg of caffeine (e.g., 5 espressos) per day from all sources (including coffee, soft drinks, energy drinks, chocolate, and medications) based on the CCQ\* Alcohol: If AUDIT-C\*\* scores more than 4 for men and more than 3 for women Note: Participants will complete a history update questionnaire at each laboratory visit to report any changes relevant to the exclusion criteria. If a participant no longer meets the eligibility criteria at any visit after the baseline assessment, the visit will either be rescheduled, if appropriate, or the participant will be withdrawn from the study. Reimbursement will be provided on a prorated basis. \*CCQ: Caffeine Consumption Questionnaire \*\*AUDIT-C: Alcohol Use Disorders Identification Test-C