How caffeine affects the visual brain

INTERVENTION: Twenty healthy young (18‐35 years) adults will be recruited and screened to ensure healthy eyes and vision. The screening includes a visual acuity test, determination of spectacle prescription, and brief ocular health examination. The main task is a measure of ocular dominance, where observers will look at patterns on a computer monitor and make judgments (by pressing a button) about the colour of a pattern that alternates between red and green. Both eyes need to be open (blinking allowed) during the main task for ocular dominance to be measured. There will be two test sessions, a treatment session and control session. The order of the sessions will be randomised and the participants blinded to the treatment. Participants will be instructed not to consume caffeine for 12 hours prior to attending each test session. At the beginning of each test session, participants will undergo baseline testing of the main ocular dominance task (15 minutes). This will be followed by: (1) a controlled dose of caffeine in the form of a single ‘No Doz Plus’ pill, which consists of 100 mg caffeine, 10 mg thiamine hydrochloride (Vitamin B1) and 10 mg nicotinic acid (Vitamin B3), or (2) a placebo pill (single ‘Betamin’ pill, which consists of 100 mg thiamine hydrochloride (Vitamin B1). Participants will wait 30 minutes for the pill to reach its peak effect, and then the participant's dominant eye will be patched for 90 minutes. Post‐patching ocular dominance tests (repeat of baseline tests, 15 minutes) will be conducted at the end of the session. During the 120 minutes of waiting, participants will be asked to sit quietly in a room and can undertake activities such as reading, watching a movie, or working on a laptop. At the second visit at least CONDITION: Eye ‐ Normal eye development and function Neurological ‐ Studies of the normal brain and nervous system Vision impairment; ; Vision impairment PRIMARY OUTCOME: Participants will observe a small striped patch in the middle of a computer monitor and make judgments (by pressing a button) about the colour of the pattern, as it alternates between red and green. The change in ocular dominance will be calculated, which compares the relative colour judgments before and after treatment.[Baseline (prior to treatment) compared to 120 minutes post‐tablet ingestion and eye patching] SECONDARY OUTCOME: None[N/A] INCLUSION CRITERIA: 1) Visual acuity at least 6/7.5 in both eyes 2) Good general health