 A total of 30 subjects will be recruited from UIW and RSO students, staff, faculty and patients. The age range will be 18 to 65 years and the investigators will attempt to include comparable numbers of male and female participants. Inclusion criteria include visual acuity of at least 2020 in each eye with no evidence of ocular, systemic or neurologic disease or ocular trauma. Based on prior research using repeated-measures designs, a difference of 0.1 log CS is considered significant and the estimated standard deviation is 0.13 log units. Hence the effect size mean differenceSD 0.10.13 0.76. The estimated minimum number of subjects to achieve significance at the 5 level with a power of 80: 1effect size2 x 16 10.762 x 16 28 subjects.8,9. Hence 30 subjects will be recruited to account for subject attrition during the course of the study. Prior to obtaining written informed consent, each subject will be briefed on the nature of the study by one or more members of the research team. Subjects will be informed that they will be evaluated with standard vision tests one hour after consuming a chocolate bar to assess its effects on performance. The dark chocolate and milk chocolate bars to be used are commercially available from Trader Joes and have comparable ingredients and nutrients except for the higher percentage 72 of cacao dark chocolate in the experimental bar while the control bar contains 31 milk chocolate cocao solids which are not associated with acute beneficial effects on performance. As stated in the informed consent document, subjects will be asked if they have allergies to any of the ingredients contained in the chocolate bars, and will be excluded from participating if they answer affirmatively. As noted above, any subjects with ocular, systemic or neurologic disease, including diabetes and hypoglycemia, will not be allowed to participate in the study. 